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Contract Towers Are More Cost Effective Than Comparable FAA Towers and Have

Similar Safety Records

Report No. AV2020028

April 28, 2020

What We Looked At Established in 1982 at 5 low-activity control towers, the Federal Aviation Administration’s (FAA) Contract Tower (FCT) Program currently consists of 254 contract towers in 46 states operated by 3 contractors and the Air National Guard. Managing about 28 percent of the Nation’s air traffic control operations, contract towers constitute an essential part of the National Airspace System (NAS). Our audit objective was to assess the FCT Program’s cost effectiveness and safety record. We statistically grouped towers based on characteristics that affect air traffic controller and tower workloads. Specifically, we gathered and examined hours of operations, numbers of takeoffs and landings, types of aircraft handled, and runway configurations. Based on these characteristics, we used two statistical methods to group 351 air traffic control towers, consisting of 248 contract towers and 103 lower level FAA towers. Our methods produced groups containing a mixture of comparable FAA and contract towers. We determined the towers within each group were similar to each other and then analyzed and directly compared their cost and safety data. We reviewed cost and safety data between fiscal years 2015 and 2018 for the universe of 351 towers.

What We Found Between fiscal years 2015 and 2018, contract towers were more cost effective per aircraft handled than comparable FAA towers, and that the safety records of contract and comparable FAA towers were similar. On average, contract towers used at least 47.6 percent fewer resources—or incurred lower controller staffing costs—per aircraft handled per year even though comparable FAA towers handled more total flights. Furthermore, while contract towers had statistically fewer safety events per aircraft handled, we do not believe the difference between these numbers and those of FAA’s towers is meaningful because, among other reasons, the numbers of safety related events across the NAS were very low relative to the total number of flights.

Our Recommendations We are making no recommendations.

Contract Towers Are More Cost Effective Than Comparable FAA Towers and Have Similar Safety Records Requested by the U.S. House of Representatives Committee on Transportation and Infrastructure and its Subcommittee on Aviation

Federal Aviation Administration | AV2020028 | April 28, 2020

All OIG audit reports are available on our website at www.oig.dot.gov.

For inquiries about this report, please contact our Office of Government and Public Affairs at (202) 366-8751.

http://www.oig.dot.gov/

AV2020028

Contents Memorandum 1

Background 3

Results in Brief 6

Contract Towers Are More Cost Effective and Have Safety Records Similar to Those of Comparable FAA Towers 7

Conclusion 12

Recommendations 13

Agency Comments and OIG Response 13

Actions Required 13

Exhibit A. Scope and Methodology 14

Exhibit B. Entities Visited or Contacted 18

Exhibit C. List of Acronyms 20

Exhibit D. Cost Comparisons 21

Exhibit E. Comparisons of Safety Events 26

Exhibit F. List of 248 Contract Towers 28

Exhibit G. List of 103 FAA-Operated Towers 35

Exhibit H. Detailed Scope and Methodology 38

Exhibit I. Major Contributors to This Report 65

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Memorandum Date: April 28, 2020

Subject: Contract Towers Are More Cost Effective Than Comparable FAA Towers and Have Similar Safety Records | Report No. AV2020028

From: Matthew E. Hampton Assistant Inspector General for Aviation Audits

To: Federal Aviation Administrator

The Federal Aviation Administration’s (FAA) Contract Tower (FCT) Program consists of 254 contract towers1 in 46 states operated by 3 contractors and the Air National Guard. Contract towers constitute an essential part of the National Airspace System (NAS) because they manage about 28 percent of the Nation’s air traffic control operations. FAA conducts benefit-cost analyses (BCA) to support decision-making for establishing and discontinuing towers, and determining the share of towers’ operating costs that airport sponsors will pay.2

Recognizing the program’s importance, the former Chairmen of the U.S. House of Representatives Committee on Transportation and Infrastructure and its Subcommittee on Aviation requested that we update our previous work on contract towers.3 Our audit objective was to assess the FCT Program’s cost effectiveness4 and safety record.5

We conducted this audit in accordance with generally accepted Government auditing standards. Exhibit A details our overarching scope and methodology. Exhibit B lists the entities we visited or contacted, and exhibit C presents a list of acronyms. This report also contains a detailed scope and methodology in exhibit H.

1 As of January 1, 2019, FAA added the Albert J. Ellis Airport in Richlands, NC, and the North Texas Regional Airport-Perrin Field in Dennison, TX, to FCT, bringing the total number of contract towers to 256. 2 49 U.S.C. § 47124 stipulates when FAA should conduct benefit-cost analyses. 3 See Contract Towers Continue To Provide Cost-Effective and Safe Air Traffic Services, but Improved Oversight of the Program Is Needed (OIG Report No. AV-2013-009), November 5, 2012. 4 We define “cost effectiveness” as the use of fewer resources per aircraft handled than comparable towers. 5 We will present the results of our work on the status of the revisions to the BCA, our second audit objective, in a future report.

U.S. DEPARTMENT OF TRANSPORTATION OFFICE OF INSPECTOR GENERAL

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We appreciate the courtesies and cooperation of Department of Transportation representatives during this audit. If you have any questions concerning this report, please call me at (202) 366-0500, or Nelda Z. Smith, Program Director, at (202) 366-2140.

cc: The Secretary DOT Audit Liaison, M-1 FAA Audit Liaison, AAE-100

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Background In 1982, FAA began a program that contracted air traffic control services at five low-activity control towers that had been closed as a result of the Professional Air Traffic Controllers Organization’s strike the previous year. In 1998, Congress provided funding for a cost-sharing program6 for existing contract towers that would otherwise have been ineligible for the FCT Program. During 2008’s economic downturn, FAA suspended admittance of new towers to the program. In 2012, Congress capped local cost-share contributions at 20 percent of total costs.

In our 2012 report, we stated that contract towers provided air traffic control services at lower costs than similar FAA towers. We reported that on average, a contract tower cost about $1.5 million less to operate than a comparable FAA tower, primarily due to lower staffing and salary levels. We also reported that contract towers had lower numbers and rates of safety events than similar FAA towers, and that airspace users supported the FCT Program.

In November 2017, FAA began to allow new and replacement towers built by airport sponsors to enter the FCT Program.7 Currently, FAA has no process for converting existing Agency towers to contract towers,8 or converting contract towers back to FAA towers.

To assess the relative cost-effectiveness and safety of contract and FAA towers, we grouped towers with similar characteristics. To develop the groups, we examined the numbers of takeoffs and landings, types of aircraft handled, and runway configurations—characteristics that affect air traffic controller and tower workloads. Using FAA definitions, we identified five types of aircraft operations (see table 1)

6 The cost-share program allows existing contract towers that fall below the established benefit-cost threshold to remain in the program by paying a portion of the costs to operate their tower. 7 FAA Order JO7210.78, FAA Contract Tower (FCT) New Start and Replacement Tower Process, November 29, 2017. 8 The last FAA tower converted to a contract tower in 1999.

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Table 1. Types of Aircraft Operations

Source: FAA

We further determined whether each tower manages aircraft from a single runway or from multiple crossing, converging, or parallel runways. Based on these characteristics, we used two statistical methods to group a universe of 351 air traffic control towers, consisting of 2489 contract towers (see exhibit F for a list) and 103 comparable FAA towers (see exhibit G for a list).10 We used one statistical method as the primary method to develop our results and the other method as a robustness check.11 Application of these statistical methods, described in exhibit H, resulted in four groups, each containing a mixture of FAA and contract towers that shared similar characteristics. See table 2 for the breakdown of the number of FAA and FCT towers in each group. Because we determined the towers within each group were similar to each other, we could analyze and directly compare their cost and safety data. We used data for the universe of 351 towers collected between fiscal years 2015 and 2018.

9 From the universe of 254 contract towers, we excluded 6 that the Air National Guard operates. 10 We considered only FAA towers with radar operating in Class C or D airspace because all contract towers operate in these airspaces. Class C airspace is generally airspace from the ground to 4,000 feet above an airport control tower. Class D airspace is generally airspace from the ground to 2,500 feet above an airport control tower. 11 A robustness check determines whether results change when using alternative assumptions or methods. When the results of a robustness check correspond with the results from a primary analysis, the results corroborate the main results.

Aircraft Operations Definition

Air carrier Operations of aircraft with seating capacities of over 60 or maximum payload capacities of over 18,000 pounds carrying passengers or cargo for hire or compensation.

Air taxi Operations of aircraft with seating capacities of 60 or less, or maximum payload capacities of 18,000 pounds or less, carrying passengers or cargo for hire or compensation.

General aviation All civil aircraft operations not classified as air carrier or air taxi.

Military All military takeoffs and landings at both FAA and FCT facilities.

Local Aircraft operations that remain in the local traffic pattern, execute low passes at the airport, and operate between the airport and a designated area within a 20−mile radius.

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Table 2. Tower Groups

Group FAA FCT

1 29 17

2 17 44

3 12 71

4 45 116

Totals 103 248

Note: To prevent competitive advantage or disadvantage in current or future FCT contract bidding, we do not specify which FAA or contract towers are included in each group. In our detailed scope and methodology (exhibit H), we include summary statistics for each group and describe the process we used to arrive at our conclusions. Source: OIG

The groups have the following characteristics:

• Group 1 handles the highest average number of total aircraft per hour (22.5), the highest average number of general aviation aircraft (8.3), and the highest average number of air carrier aircraft per hour (2.8). It also has a mixture of parallel runway configurations with some converging runways. In this group, for example, FAA operates Brackett Field (POC) in California, while contractors operate Brown Field Municipal (SDM) in California.

• Group 2 handles the second highest average number of total aircraft per hour (14.7) and on average the most military aircraft per hour (1.0). It contains no single runway configurations. In group 2, for example, FAA operates Nantucket Memorial (ACK) in Massachusetts, while contractors operate Front Range (FTG) in Colorado.

• Group 3 handles the third highest average total number of aircraft per hour (13.8), the second highest average number of general aviation aircraft, and the lowest average number of air carrier aircraft. All towers in this group have just one runway. In this group, for example, FAA operates San Gabriel Valley (EMT) in California and contractors operate Bellingham International (BLI) in Washington.

• Group 4 handles the lowest average number of total aircraft per hour (13.0), but handles more air carrier aircraft than Group 3. It has crossing and parallel runway configurations. In group 4, for example, FAA operates Flying Cloud (FCM) in Minnesota while contractors operate Dothan Regional (DHN) in Alabama.

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The level of air traffic control complexity differs based on many factors. Factors such as aircraft speed and performance; runway and taxiway layout, length, and capacity; airspace class; terrain; proximity to other airports; interaction with foreign countries; and military operations all effect the complexity of air traffic control. We created our groupings based on numbers of takeoffs and landings, types of aircraft handled, and runway configurations.

Results in Brief Contract towers are more cost effective than comparable FAA towers and have similar safety records.

To compare contract and FAA towers for this review, we grouped 351 air traffic control towers with similar characteristics, and examined the numbers of takeoffs and landings, types of aircraft handled, and runway configurations—characteristics that affect air traffic controller and tower workloads. We found that between fiscal years 2015 and 2018, contract towers were more cost effective per aircraft handled than comparable FAA towers, and that the safety records of contract and comparable FAA towers were similar. On average, contract towers used at least 47.6 percent fewer resources than comparable FAA towers.12 Contract towers on average used fewer resources—or incurred lower controller staffing costs—per aircraft handled per year even though comparable FAA towers handled more total flights. Furthermore, while contract towers had statistically fewer safety events per aircraft handled, we do not believe the difference between these numbers and those of FAA’s towers is meaningful because, among other reasons, the numbers of safety related events across the NAS were very low relative to the total number of flights.

We are making no recommendations.

12 The 47.6 percent fewer resources is based on operating costs without overhead. See table 4.

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Contract Towers Are More Cost Effective and Have Safety Records Similar to Those of Comparable FAA Towers

Based on our methodology, contract towers use fewer resources than comparable FAA towers. Furthermore, the safety records of contract and comparable FAA towers are similar.

Contract Towers Use on Average Fewer Resources Per Aircraft Handled

Based on our methodology, contract towers on average use fewer resources13 per aircraft handled than comparable FAA towers. For the purposes of this report, we define “use of fewer resources” as cost effectiveness. In this context, cost equals the sum of all costs for fiscal years 2015 through 2018 divided by the total number of aircraft operations during the same time period.

We found that between fiscal years 2015 and 2018, contract towers were more cost effective per aircraft handled than FAA towers with similar runway configurations and mix of air traffic. On average, they used at least 47.6 percent fewer resources14 than comparable FAA towers (see table 4, Group 4). In our analysis, we examined the following tower operating costs:

• Labor and Benefits Costs. We first considered labor costs, including all labor and benefits payments. The average labor and benefits cost of operating a contract tower is between $10.45 and $21.02 lower per aircraft handled than those of comparable FAA towers (see table 3).

13 “Resources” refers primarily to controller staffing costs. The methodologies used to determine controller staffing at FAA and contract towers differ. At FAA towers, staffing is determined by FAA’s Office of Labor Analysis which bases crew shifts on the numbers of air traffic operations and minutes of communication required. Contract tower staffing levels are determined by each contractor and then approved by FAA. Contract towers must have staff of at least the equivalent of four full-time controllers. 14 For example, if an FAA tower’s cost per aircraft was $25.87 and a contract tower’s cost per aircraft was $13.55, then the contract tower uses 47.6 percent fewer resources per aircraft handled.

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Table 3. FAA and Contract Tower Controller and Labor Costs for Fiscal Years 2015 through 2018a

Costs Group 1 Group 2 Group 3 Group 4

Average total FAA labor and benefits $15,735,462.12 $15,091,367.00 $10,817,413.79 $11,400,187.53

Average FAA labor and benefits cost per aircraft handled

$22.34 $29.63 $19.93 $22.89

Average total contract tower labor and benefitsb $2,676,222.39 $2,410,237.62 $2,304,554.78 $2,311,141.44

Average contract tower labor and benefits cost per aircraft handled

$7.41 $8.61 $9.48 $10.87

Difference in average FAA and contract tower labor and benefits cost per aircraft handled

$14.93 $21.02 $10.45 $12.02

Average percent fewer resources used by comparable contract towers

66.8% 70.9% 52.4% 52.5%

a Please see exhibit D for included cost categories. All figures are within-group averages, including totals. b Total contract tower labor cost includes fringe benefits for contract controllers. Source: OIG analysis.

• Operating Costs without Overhead.15 We then looked at all costs except overhead, including labor costs, utilities, telecommunications, and leases, among others. Contract towers’ average cost per aircraft handled is between $10.67 and $23.06 lower than FAA counterpart towers (see table 4).

15 The term “overhead costs” refers to the cost of indirect support services provided by FAA staff offices—such as human resources management—and ATO’s Chief Operating Officer.

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Table 4. FAA and Contract Towers Operating Costs without Overhead during Fiscal Years 2015 through 2018


Average FAA cost per aircraft handled $25.17 $33.85 $21.95 $25.87

Average contract tower cost per aircraft handled $8.90 $10.80 $11.28 $13.55

Difference in average FAA and contract tower operating costs per aircraft handled (not including overhead)

$16.26 $23.06 $10.67 $12.32

Average percent fewer resources used by comparable contract towers 64.6% 68.1% 48.6% 47.6%

Note: Please see exhibit D for included cost categories. All figures are within-group averages, including totals. Due to rounding, some figures may be higher or lower than the sum. Source: OIG analysis.

• Operating Costs including Overhead. We then looked at operating costs including overhead and found that contract tower overhead costs average remained between $12.64 and $27.20 less per aircraft handled than FAA counterpart towers (see table 5).

Table 5. FAA and Contract Towers Operating Costs Including Overhead during Fiscal Years 2015 through 2018


Average FAA cost per aircraft handled $29.74 $39.91 $25.93 $30.51

Average contract tower cost per aircraft handled $10.50 $12.71 $13.29 $15.94

Difference in average FAA and contract tower operating costs per aircraft handled (including overhead)

$19.24 $27.20 $12.64 $14.57


Note: Please see exhibit D for included cost categories. All figures are within-group averages, including totals. Source: OIG analysis.

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The Safety Records of FAA and Contract Towers are Comparable

Based on our methodology, contract towers have experienced statistically fewer safety events per aircraft handled than FAA towers. However, in our opinion, these differences are not meaningful because at both contract and FAA towers, numbers of reported safety events are very low relative to total flights, which is in the single digits per million aircraft handled. Moreover, many of these events are self-reported, and both a mandatory and voluntary report may be submitted for a single safety event.

Within each of our tower groups, safety events were rare in all metrics. For example, of the 351 towers we analyzed, 242 towers (68.95 percent) did not report a single air traffic controller involved risk analysis event or surface risk analysis event16 between fiscal years 2015 and 2018 (see table 6). These 351 towers handled on average 84,328 total aircraft per year. Only 19 towers—17 FAA and 2 contract—handled over 220,000 total aircraft per year. Furthermore, FAA towers that we analyzed averaged 8.24 controller-involved reported risk analysis events and reported surface risk analysis events per 1 million aircraft handled, while contract towers in our analyses averaged not more than 1.08 events per 1 million aircraft handled.17

16 See exhibit A for definitions of “risk analysis event” and “surface risk analysis event.” 17 ANC in Anchorage, AK, an FAA tower, is responsible for 1.89 of the 8.24 events per million aircraft handled during the sample period.

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Table 6: Towers with Risk Analysis and Surface Risk Analysis Events Involving an Air Traffic Controller During Fiscal Years 2015 through 2018

Aircraft Handled and Events Group 1 Group 2 Group 3 Group 4

FAA average aircraft handled per year 176,086 127,340 135,711 124,513

FCT average aircraft handled per year 90,263 69,998 60,778 53,160

Average number of risk analysis and surface risk analysis events involving air traffic controllers per million aircraft handled at FAA towers

10.97 7.04 7.37 6.47

Average number of risk analysis and surface risk analysis events involving air traffic controllers per million aircraft handled at FCTs

2.28 1.06 0.52 1.18

Total risk analysis and surface risk analysis events involving air traffic controllers per million aircraft handled

8.96 3.53 2.40 3.70

Note: FAA measures collision opportunity as the number of potential pairs of aircraft—a function of the square of the number of aircraft operating in the area (see FAA-APO-90-7, Establishment and Discontinuance Criteria for Airport Traffic Control Towers, August 1990). Consequently, we would expect increasingly higher numbers of reports of safety incidents per operation as the number of aircraft handled increases. Source: OIG analysis.

In our 2012 report, we noted FAA’s transition to a new approach to safety oversight at all air traffic facilities. Prior to October 2010, FAA’s air traffic facility oversight included facility safety evaluations of both FAA and contract towers every 3 years. In January 2012, FAA transitioned to risk-based oversight of its air traffic facilities. Under the new system, FAA analyzes safety event data reported by air traffic controllers to identify specific safety problems or trends at air traffic facilities. FAA then focuses its oversight based on these analyses.

Since implementing the new system, FAA has completed a higher number of external compliance verifications (ECV) at FAA towers than contract towers. An ECV is a safety review conducted onsite by FAA’s Safety Quality Control Group based on risks associated with reported events and other quality control data along with observed trends. Between fiscal years 2015 and 2018, FAA conducted ECVs at 96 (93.2 percent) of the 103 FAA towers we reviewed. Several of these 96 towers received multiple ECVs. During the same time period, FAA conducted ECVs at 76 (30.6 percent) of the 248 contract towers we reviewed. This trend may be attributable to the fact that FAA towers handle more aircraft and have a higher number of reported safety events.

The FCT contract requires contractors to have quality assurance programs that include internal facility evaluations. Each contractor has established its own

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quality assurance program and conducts evaluations of its towers. FAA does not perform regular reviews of these programs. Instead, the Agency relies on contractors’ annual self-evaluations to assess contract tower performance and identify areas for improvement.

In fiscal year 2008, FAA implemented a voluntary safety reporting program known as the Air Traffic Safety Action Program (ATSAP) at air traffic facilities. A voluntary safety reporting program provides a confidential, but not anonymous, non-punitive mechanism for employees to report aviation safety events and non-compliance with FAA directives and Federal safety regulations. Reporters use their discretion in writing the reports, which they submit electronically to a review committee. However, for an event involving national security or the immediate safety of a flight, a mandatory report must be completed irrespective of a voluntary report.

In our 2012 audit report, we recommended that FAA implement a similar voluntary safety reporting program at contract towers to ensure more comprehensive reporting of safety events. In response, in fiscal year 2015, FAA established the SAFER-FCT18 program at contract towers. Contract and FAA-operated towers now have the same safety requirements and methods for reporting safety events. However, it is important to note that FAA personnel voluntarily report significantly more safety events than contract tower personnel do. Between fiscal years 2015 and 2018, controllers at the 103 FAA towers we reviewed made over 7,000 voluntary reports while contract tower controllers made 574. We did not find any particular reason for this reporting disparity, though FAA personnel’s greater exposure and familiarity with voluntary reporting may result in more reports.

Conclusion The FCT Program allows FAA to contract out the operation of some lower-activity control towers at airports which otherwise would not be able to offer air traffic control services. In addition to providing tower services at lower cost and with similar levels of safety, the Program is important because it connects smaller airports and rural communities to the national air transportation system. Consequently, the FCT Program continues to be a viable alternative for FAA to provide cost effective and safe air traffic services to aviation users and the flying public.

18 The voluntary safety reporting program for contract towers is called SAFER-FCT or the federal contract towers safety action program.

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Recommendations We are not making any recommendations.

Agency Comments and OIG Response We provided a draft of this report to FAA on March 16, 2020. On April 6, 2020, we were notified that the Department would not be issuing a written response. Throughout the review, we discussed our methodology, findings, and conclusions with FAA representatives. Where appropriate, we incorporated FAA’s comments and input received during our meetings at both FAA headquarters and field locations.

Actions Required No actions required.


Exhibit A. Scope and Methodology We conducted this performance audit between August 2018 and March 2020, in accordance with generally accepted Government auditing standards as prescribed by the Comptroller General of the United States. Those standards require that we plan and perform the audit to obtain sufficient, appropriate evidence to provide a reasonable basis for our findings and conclusions based on our audit objectives. We believe that the evidence obtained provides a reasonable basis for our findings and conclusions based on our audit objectives.

The Chairmen of the U.S. House of Representatives Committee on Transportation and Infrastructure and its Subcommittee on Aviation requested that we update our prior work. Our audit objectives were to assess (1) the FCT Program’s cost effectiveness and safety record and (2) the status of the benefit-cost analysis revisions. In this report, we present the results of our work on the program’s cost effectiveness and safety record. We will present the results of our work on the status of the benefit cost analysis revisions in a separate report.

We interviewed officials at FAA Headquarters and two of three regional offices about different aspects of the FCT program. We selected the two regional offices based on availability. We conducted site visits at 5 of 103 FAA towers that we selected based on our statistical groupings and proximity. We also visited 12 of 248 contract towers that we statistically selected. To make this selection, we used a two-stage stratified probability proportional to size sample in which size was the 5-year tower operations average. We met with the air traffic managers at these towers and the airport directors or representatives at the contract towers to discuss the towers’ air traffic operations. We also met with the three FCT Program contractors.

To gain perspective on the cost effectiveness and safety of contract towers, we interviewed aviation industry officials at three trade groups, including the American Association of Airport Executives, the Aircraft Owners and Pilot Association, and the National Air Transportation Association. We also interviewed National Air Traffic Controllers Association officials to obtain air traffic controllers’ perspective on the cost effectiveness and safety of contract towers.

To assess the cost effectiveness and safety record of contract towers, we grouped towers based on characteristics that affect air traffic controller and tower workloads. To compare similar towers, we gathered and examined hours of operations, numbers of takeoffs and landings, types of aircraft handled, and runway configurations provided by FAA’s ATO. We also gathered and validated operations data using the Operations Network (OPSNET), the official source of NAS air traffic operations and delay data. To validate the contract towers’ hours of operations, we used the seven FCT Program contracts and contract


modifications. We validated the hours of operation for FAA towers using data from FAA’s Office of Labor Analysis. To validate ATC levels for FAA towers, we used data from FAA's Office of Labor Analysis and ATO Staffing Workbook. We found the data reliable enough for the purposes of this audit.

We identified five types of aircraft operations—air carrier, air taxi, general aviation, military, and local. We also determined whether each tower managed aircraft from a single runway or multiple crossing, converging, or parallel runways. Based on these characteristics, we used two statistical methods (see exhibit H) to group a universe of 351 air traffic control towers, consisting of 248 contract towers (see exhibit F for a list) and 103 comparable FAA towers (see exhibit G for a list). We arrived at 248 contract towers from a universe of 254 by excluding 6 towers operated by the Air National Guard. We arrived at the 103 comparable FAA towers from a list of 264 by excluding towers (1) whose ATC levels were 9 or above19 because they would be more complex and have more traffic operations than contract towers; (2) that were co-located with terminal radar approach control facilities (TRACON) because they would not be comparable to contract towers in staffing and operational purposes; or (3) that did not operate in Class C or D airspace because contract towers operate only in Class C or D airspace.

Our methods resulted in four groups that we used to analyze cost and safety data between fiscal years 2015 and 2018. We used one method as the primary method to report our results and the second method as a robustness check. Our methodology was reviewed by Michael Simeone, of Arizona State University, and Jacob LaRiviere of Microsoft; they both found it to be sound.

We received extensive cost data from FAA’s Office of Financial Operations for both FAA operated and contract towers. See exhibit D for the cost categories we used in the cost effectiveness analysis. Within each statistical group, we compared cost metrics among FAA and contract towers. We analyzed costs in three ways—air traffic control labor/benefit costs only; operating costs without overhead; and operating costs including overhead. We compared each cost category on a per aircraft basis because some towers handled more aircraft than others. We validated FAA’s air traffic control labor and benefit liability expenditures for FAA towers using FAA's payment records downloaded from Delphi, DOT’s automated financial accounting system. We validated contract controller labor costs by comparing the monthly service invoices submitted by the FCT contractors to the costs approved and paid by FAA.

19 Each FAA facility is classified as a level 4 through 12, based on numerous factors including traffic volume, complexity and sustainability of traffic.


Using the same groups and statistical methods, we examined seven safety events (see exhibit E) and reported on the following:

• Numbers of risk analysis events involving an air traffic controller. A risk analysis event is a loss of standard separation between aircraft that requires analysis to determine severity and chance of reoccurrence;

• Numbers of surface risk analysis events involving an air traffic controller. A surface risk analysis event occurs when there is less than 6,000 feet of separation between two aircraft on a runway or when an aircraft lands or departs from a taxiway or closed runway;

• Numbers of FAA ATSAP and contractor SAFER-FCT reports. ATSAP and SAFER-FCT reports are voluntary, non-punitive, confidential written accounts of air traffic safety events; and

• Numbers of completed ECVs. An ECV is a safety review conducted onsite by FAA’s Safety Quality Control Group. ECVs are conducted based on risks associated with reported events and other quality control data along with observed trends.

We obtained the safety data from FAA’s Office of Safety and Technical Training that included information from several FAA databases—Comprehensive Electronic Data Analysis and Reporting (CEDAR),20 Compliance Verification Tool (CVT),21 ATSAP, and SAFER-FCT. The risk analysis and surface risk analysis events came from CEDAR, ECV data came from CVT, and the voluntary safety reports for FAA and contract towers came from separate systems called ATSAP and SAFER-FCT. Officials at FAA’s Office of Safety and Technical Training confirmed that the Agency provided all available safety data to us and that all the information had been either self-reported through internal databases or evaluated by ATO’s safety program.

We identified the following limitations in our methodology:

1. Grouping methods, while widely used, are limited to available data and inputs. Differences between towers may exist that affect towers’ operational costs and safety but are not fully captured by aircraft operations and runway configurations.

20 CEDAR is a web-based, comprehensive data reporting, collection, and analysis tool used by both FAA quality control and quality assurance. 21 CVT is a national database that contains checklists, reports, facility information, tracking information, response data, and other statistical information related to FAA’s compliance verification process.


2. The average FAA tower handled more passengers than the average contract tower within each group. We did not account for the numbers of passengers handled by each tower.

3. Our cost differential calculations did not account for several factors relevant primarily to FAA towers. First, most FAA towers use some resources to train new air traffic controllers. Second, locality pay may be more of a consideration for FAA towers, which tend to be located in more heavily populated areas than comparable contract towers. Third, while FAA approves staffing levels at contract towers, contract towers are generally staffed at lower levels than FAA towers. FAA also has more towers that operate overnight shifts, and requires overnight shifts to be covered by at least two controllers.22

4. Numbers of reported safety events were very low relative to overall aircraft operations for all towers. Based on our methodology, contract towers experience statistically fewer safety events per aircraft handled than FAA towers. However, we believe that these differences are not statistically meaningful due to the rarity of safety events.

22 Three of 248 contract towers operate 24 hours a day, 7 days a week (1.2 percent), while 26 of 103 FAA-operated towers (25.2 percent) operate this way.


Exhibit B. Entities Visited or Contacted

FAA Headquarters, Washington, DC Air Traffic Organization (ATO)

• FAA Contract Tower Program Office

• Office of Safety and Technical Training

Office of Finance and Management

• Office of Financial Services

• Office of Labor Analysis

Policy, International Affairs and Environment

• Office of Aviation Policy and Plans

FAA Field Locations • ATO, Office of Safety and Technical Training, Service Center, Quality

Control Group, College Park, Georgia and Fort Worth, Texas

FAA Air Traffic Control Towers • Van Nuys, California (VNY)

• Pensacola International, Florida (PNS)

• Dekalb-Peachtree, Georgia (PDK)

• Lakefront, Louisiana (NEW)

• Manassas Regional/Harry P Davis Field, Virginia (HEF)

FAA Contract Towers • Whiteman, California (WHP)

• Redding Muni, California (RDD)


• Destin Executive, Florida (DTS)

• Northwest Florida Beaches International, Florida (ECP)

• Lewiston-Nez Perce County, Idaho (LWS)

• Idaho Falls Regional, Idaho (IDA)

• Frederick Muni, Maryland (FDK)

• Easton/Newnam Field, Maryland (ESN)

• Santa Fe Muni, New Mexico (SAF)

• Four Corners Regional, New Mexico (FMN)

• Lawrence J Timmerman, Wisconsin (MWC)

• Kenosha Regional, Wisconsin (ENW)

FCT Program Contractors • Midwest Air Traffic Control Service, Inc.

• Robinson Aviation (RVA), Inc.

• Serco, Inc.

Other Organizations • American Association of Airport Executives (AAAE)

• Aircraft Owners and Pilots Association (AOPA)

• National Air Transportation Association (NATA)

• National Air Traffic Controllers Association (NATCA)

Reviewers • Michael Simeone, Director of Data Science and Analytics for Arizona State

University Libraries

• Jacob LaRiviere, Principal Researcher, Microsoft, Inc.

Exhibit C. List of Acronyms 20

Exhibit C. List of Acronyms ATC air traffic controller

ATO Air Traffic Organization

ATSAP Air Traffic Safety Action Program

DOT Department of Transportation

ECV external compliance verification

FAA Federal Aviation Administration

FCT FAA contract tower

NAS National Airspace System

OIG Office of Inspector General


Exhibit D. Cost Comparisons We consulted with FAA’s Office of Financial Operations to determine what cost categories FAA tracks for both FAA operated and contract towers. We used FAA financial data to compare and analyze the cost associated with operating FAA and contract towers. We conducted three cost comparison—air traffic controller (ATC) labor and benefits only; total costs without overhead; and total costs including overhead.

In our ATC labor and benefits costs comparisons:

Cost categories included FAA or FCT cost

FAA ATC labor FAA

FAA ATC benefit liabilities FAA

Contract controller labor FCT

In our total costs without overhead comparisons:

Cost categories included FAA or FCT Cost

FAA ATC labor FAA



FAA ATC non-labor FAA

Technical operations labor Both

Technical operations benefit liabilities Both

Technical operations non-labor Both

FCT Insurance FCT

Logistics Both

Telecommunications Both

Utilities Both

Leases Both

Note. Some FAA towers did not incur utilities and leases costs. Furthermore, our analysis did not include costs incurred by airport sponsors. As a result, some contract towers did not have technical operations labor, technical operations benefit liabilities, technical operations non-labor, logistics, telecommunications, utilities, and leases costs.


In our total costs including overhead comparisons:

Cost categories included FAA or FCT Cost

FAA ATC labor FAA



FAA ATC non-labor FAA

Technical operations labor Both

Technical operations benefit liabilities Both

Technical operations non-labor Both

FCT insurance FCT

Logistics Both

telecommunications Both

Utilities Both

Leases Both

FAA Headquarters indirect support (overhead) Both

ATO indirect support (overhead) Both

Note. Some FAA towers did not incur utilities and leases costs. Furthermore, our analysis did not include costs incurred by airport sponsors. As a result, some contract towers did not have technical operations labor, technical operations benefit liabilities, technical operations non-labor, logistics, telecommunications, utilities, and leases costs. Lastly, contract towers that are airport sponsored, owned, and maintained had no ATO indirect support costs.

Descriptions of Cost Categories 1. FAA ATC labor. Includes the compensation and benefits of personnel

directly associated with providing ATC services at terminal locations.

2. FAA ATC benefit liabilities. FAA recognizes the full cost of pensions and other retirement benefits during an employee’s active years of service through a combination of costs financed by FAA’s appropriations and imputed costs. Although it is not funded by FAA’s annual operations appropriation, the liability represents a cost to the Federal Government. The portion of unfunded benefit costs for air traffic controllers is computed for each facility, and is therefore directly traceable.


3. Contract controller labor. Includes contract labor cost associated with ATC services at contract tower locations only. Controller labor costs paid by FAA are collected from invoices submitted by vendors for air traffic services provided during the year. These invoices may include wage determination adjustments for the last quarter of the immediate prior year if known at the time cost is compiled.

4. FAA ATC non-labor. Includes costs such as supplies and travel expenses that are directly associated with a specific ATC activity at each terminal location. The cost of ATC non-labor is directly traceable to the ATC service using the actual cost for each facility.

5. Technical operations’ labor. Includes the compensation and benefits of personnel that are directly associated with providing maintenance of electronics and equipment used in direct support of providing ATC service and located within the tower.

6. Technical operations’ benefit liabilities. FAA recognizes the full cost of pensions and other retirement benefits during an employee’s active years of service through a combination of costs financed by FAA’s appropriations and imputed costs. The portion of unfunded benefit costs for technicians is allocated pro rata based on labor charges to all projects, such as equipment and locations, supported by each maintenance organization since technicians may be responsible for maintaining multiple types of equipment at multiple facilities.

7. Technical operations’ non-labor. Includes costs such as guard services, ground services, and other services that are directly associated with ATC services. The cost of technical operations’ non-labor is directly traced to the equipment or facility at each tower location using the actual cost for each facility.

8. FCT insurance. Acknowledging the devastating effects associated with aircraft accidents, FAA provides aircraft accident liability insurance coverage at each of the contract tower locations. FAA has established a $10,000,000.00 per occurrence amount for each FCT location. FAA procures the brokerage services necessary to obtain the aviation liability insurance. The total cost of FCT insurance premiums paid annually and captured in FAA’s accounting system is allocated evenly to all contract towers. The total premiums paid may vary from year to year depending on insurance adjustments and timing of payments.

9. Logistics. FAA’s Logistics Center is a large depot responsible for maintaining stocks and stores of spare parts for issuance to the field, performing facility refurbishments, and providing on-site repair services. Logistics cost are obtained from raw supply data in the


Logistics Center Support System (LCSS). LCSS is used to track the issuance of equipment from the Logistics Center to the field, including part information, cost data on the part requisitioned, quantities, the requisitioning cost center, and related customer information. These costs are only included if directly traceable to equipment at the tower associated with providing ATC service.

10. Telecommunications. The cost of leased telecommunications lines to and from tower facilities, including all activities associated with maintaining, upgrading, or modifying operational and administrative communications services required for tower facilities; includes both costs from FAA’s telecommunications infrastructure program obtained from the program’s Invoice and Financial Management System, and telecommunications costs related to agreements with the Defense Information Systems Agency. The cost of telecommunications is based on actual cost directly traceable to each facility. Airport-sponsor incurred telecommunication costs are not included.

11. Utilities. Include costs such as electricity, gas, and water. Utilities costs are directly traceable to each facility in FAA’s accounting system. In some cases, utilities may be included as part of a lease agreement or may be provided by the airport sponsor. Airport-sponsor incurred utilities costs are not included.

12. Leases. Include costs of operating leases. Capital leases are established as assets and are included as depreciation. An operating lease is defined as a lease that meets none of the criteria for a capital lease. Operating lease payments are treated as charges to operating expenses, and are not capitalized as assets. In most cases, these payments are made using facilities and equipment funding. Information on lease agreements is available from FAA’s Real Estate Management System. Actual lease costs are directly traceable to each facility. Airport-sponsor incurred lease costs are not included.

13. FAA Headquarters indirect support (overhead). FAA is organized such that a majority of its general and administrative services are provided by centralized organizations, referred to as FAA staff offices. These organizations provide facility and personnel security; accounting and budget services; human resources management; Government, public, and industry affairs; legal and policy services; and executive leadership. The agency wide indirect rate to recover Headquarters indirect costs is 8.0 percent of all labor and non-labor operations and maintenance expenses. This rate is reviewed annually and updated as necessary.


14. ATO indirect support (overhead). ATO is organized with several layers of management and oversight. It has several staff offices—including the Chief Operating Officer, Management Services, Safety and Technical Training, Joint Planning and Development, and Mission Support Services—that provide support to air traffic and technical operations service units. Each service unit provides oversight and support to its service areas. Each service area provides oversight and support for the services provided by the district offices it covers. Each district office provides oversight and support to facilities. The rate for recovering ATO indirect costs is 11.0 percent of all labor operations and management expenses. The rate is reviewed annually and updated as necessary.

15. FAA ATC contract training. Includes the cost of on-site training provided under contract at select locations based on controllers’ specialized needs. A pro rata allocation is performed to assign these training costs to each terminal facility based on the actual amount of training hours invoiced by the training contractor at facility. These costs are only relevant to FAA towers.

16. FAA Academy training. The FAA Academy, located in Oklahoma City, is a large training facility that provides agency wide training services. The cost of ATC and technical operations training at the Academy includes costs for course development and delivery, and associated employee travel and per diem costs. The Academy maintains attendance records with detailed travel and course information. The portion of travel costs assigned to each tower facility is determined based on students’ travel records. These costs are only relevant to FAA towers.

17. FAA ATC medical. Air traffic controllers receive regular medical exams and drug and alcohol tests. An organization within FAA’s Office of Aviation Medicine—which resides within the Aviation Safety line of business—funds, conducts, and manages these exams and tests. Medical costs are allocated pro rata to all terminal and en route facilities based on personnel compensation and benefits cost. The current methodology does not allocate cost to FAA contract towers because these facilities do not have personnel costs and do not benefit from the medical program. These costs are only relevant to FAA towers.

Note: We excluded three costs from our comparisons—FAA ATC contract training, FAA Academy training, and FAA ATC medical—because these cost categories apply only to FAA operated facilities.


Exhibit E. Comparisons of Safety Events Safety is extremely difficult to measure. In order to conduct appropriate comparisons, we sought input from FAA and industry stakeholders to help identify safety events. Based on discussions with FAA officials and industry stakeholders, we compared the numbers of the following safety events that occurred between fiscal years 2015 and 2018.

1. Risk analysis events involving an air traffic controller. A risk analysis event is a loss of standard separation that has a measure of compliance of less than 66 percent. According to an FAA official, a risk analysis event can also be defined as an event that undergoes deeper analysis to determine severity and repeatability factors associated with an individual occurrence.

2. Surface risk analysis events involving an air traffic controller. A surface risk analysis event occurs when there is less than 6,000 feet separation on a runway between two aircraft or when an aircraft lands or departs from a taxiway or closed runway.

3. Mandatory occurrence reports by type at FAA and contract towers. A mandatory occurrence report is a self-initiated safety report by a staff person at an FAA or contract tower on an occurrence involving

airborne loss of separation,

airport surface loss of separation,

terrain/obstruction,

airborne air traffic control anomaly (airspace/altitude/route/speed) not involving a loss of separation,

airport environment,

communication,

emergency or in-flight hazard,

inquiry, or

technical operations.

4. Possibly significant events by type at FAA and contract towers. A significant event is any event in the NAS that: attracts media attention—regional, national, or both—or political attention—regional or nation or both; involves aircraft proximity with less than 33 percent of the standard;


involves a report of a near midair collision with evasive action; or requires immediate notification to the FAA service area or Headquarters.

5. Covered event reviews at FAA and contract towers. A covered event review (CER) is used to supplement and document the air traffic services rendered during an aircraft accident. A CER requires service delivery points to review each accident in depth, looking beyond areas of individual performance. A CER also includes a review of all aspects of service (individual performance, equipment issues, weather, etc.) and identifies any issues that cannot be ruled out as having contributed to the accident.

6. FAA Air Traffic Safety Action Program (ATSAP) and contractor SAFER FCT reports. ATSAP and SAFER-FCT reports are voluntary, non-punitive, confidential, written accounts of air traffic safety events.

7. Completed external compliance verifications (ECV). An ECV is a safety review conducted onsite by FAA’s Safety Quality Control Group based on risks associated with a reported event and other quality control data along with observed trends.


Exhibit F. List of 248 Contract Towers Count State Airport Name Tower ID

1 AK Bethel BET 2 AK Kenai Muni ENA 3 AK King Salmon AKN 4 AK Kodiak ADQ 5 AL Mobile Downtown BFM 6 AL Dothan Regional DHN 7 AL Tuscaloosa Regional TCL 8 AR Drake Field FYV 9 AR Northwest Arkansas Regional XNA 10 AR Rogers Executive-Carter Field ROG 11 AR Springdale Muni ASG 12 AR Texarkana Regional/Webb Field TXK 13 AZ Chandler Muni CHD 14 AZ Flagstaff Pulliam FLG 15 AZ Glendale Muni GEU 16 AZ Phoenix Goodyear GYR 17 AZ Laughlin/Bullhead International IFP 18 AZ Ryan Field RYN 19 AZ Phoenix-Mesa Gateway IWA 20 CA Castle MER 21 CA Chico Muni CIC 22 CA Fullerton Muni FUL 23 CA Jack Northrop Field/Hawthorne Muni HHR 24 CA Sacramento Mather MHR 25 CA Modesto City-Co-Harry Sham Field MOD 26 CA Oxnard OXR 27 CA Palmdale USAF Plant 42 PMD 28 CA Ramona RNM 29 CA Redding Muni RDD 30 CA Riverside Muni RAL 31 CA Sacramento Executive SAC 32 CA Salinas Municipal SNS 33 CA San Carlos SQL 34 CA Brown Field Muni SDM 35 CA San Luis County Regional SBP 36 CA Santa Maria Pub/Capt G Allan Hancock Field SMX 37 CA Southern California Logistics VCV


Count State Airport Name Tower ID

38 CA Whiteman WHP 39 CA General William J. Fox Airfield WJF 40 CO Eagle County Regional EGE 41 CO Front Range FTG 42 CO Grand Junction Regional GJT 43 CT Igor I Sikorsky Memorial BDR 44 CT Danbury Muni DXR 45 CT Groton- New London GON 46 CT Hartford-Brainard HFD 47 CT Tweed-New Haven HVN 48 CT Waterbury-Oxford OXC 49 FL Albert Whitted SPG 50 FL Boca Raton BCT 51 FL Brooksville- Tampa Bay Regional BKV 52 FL Cecil VQQ 53 FL Destin Executive DTS 54 FL Flagler Executive FIN 55 FL Gainesville Regional GNV 56 FL North Perry HWO 57 FL Jacksonville Executive at Craig CRG 58 FL Key West International EYW 59 FL Kissimmee Gateway ISM 60 FL Lakeland Linder Regional LAL 61 FL Leesburg International LEE 62 FL Melbourne International MLB 63 FL Naples Muni APF 64 FL New Smyrna Beach Muni EVB 65 FL Ocala International-Jim Taylor Field OCF 66 FL Miami-Opa Locka Executive OPF 67 FL Ormond Beach Muni OMN 68 FL Page Field FMY 69 FL Northwest Florida Beaches International ECP 70 FL Pompano Beach Airpark PMP 71 FL Punta Gorda PGD 72 FL Northeast Florida Regional SGJ 73 FL Witham Field SUA 74 FL Space Coast Regional TIX 75 GA Athens/Ben Epps AHN 76 GA Fulton County Airport-Brown Field FTY 77 GA Gwinnett County-Briscoe Field LZU



78 GA Middle Georgia Regional MCN 79 GA Cobb County International-McCollum Field RYY 80 GA Southwest Georgia Regional ABY 81 GU Guam International GUM 82 HI Ellison Onizuka Kona International at Keahole KOA 83 HI Lihue LIH 84 HI Molokai MKK 85 IA Dubuque DBQ 86 ID Friedman Memorial SUN 87 ID Idaho Falls Regional IDA 88 ID Lewiston-Nez Perce County LWS 89 ID Pocatello Regional PIH 90 IL Veterans Airport of Southern Illinois MWA 91 IL Waukegan National UGN 92 IL Central IL Regional Airport at Bloomington/Normal BMI 93 IL Decatur DEC 94 IL Southern Illinois MDH 95 IL St. Louis Regional ALN 96 IN Monroe County BMG 97 IN Columbus Muni BAK 98 IN Gary/Chicago International GYY 99 IN Delaware County Regional MIE

100 KS Topeka Regional FOE 101 KS Garden City Regional GCK 102 KS Hutchinson Regional HUT 103 KS Johnson County Executive OJC 104 KS Manhattan Regional MHK 105 KS New Century Aircenter IXD 106 KS Philip Billard Muni TOP 107 KS Salina Regional SLN 108 KY Barkley Regional PAH 109 KY Owensboro/Daviess County Regional OWB 110 LA Acadiana Regional ARA 111 LA Chennault International CWF 112 LA Houma-Terreborne HUM 113 LA Shreveport-Downtown DTN 114 MA Westfield-Barnes Regional BAF 115 MA Beverly Regional BVY 116 MA Barnstable Muni-Boardman/Polando Field HYA 117 MA Lawrence Muni LWM



118 MA Martha's Vineyard MVY 119 MA New Bedford Regional EWB 120 MA Norwood Memorial OWD 121 MA Worcester Regional ORH 122 MD Easton/Newnam Field ESN 123 MD Frederick Muni FDK 124 MD Martin State MTN 125 MD Salisbury-Ocean City Wicomico Regional SBY 126 MD Hagerstown Regional-Richard A Henson Field HGR 127 MI W K Kellogg BTL 128 MI Coleman A Young Muni DET 129 MI Jackson County- Reynolds Field JXN 130 MI Sawyer International SAW 131 MN Anoka County-Blaine (Janes Field) ANE 132 MN St. Cloud Regional STC 133 MO Branson BBG 134 MO Columbia Regional COU 135 MO Jefferson City Memorial JEF 136 MO Joplin Regional JLN 137 MP Francisco C Ada/Saipan International GSN 138 MS Golden Triangle Regional GTR 139 MS Greenville Mid-Delta GLH 140 MS Hawkins Field HKS 141 MS Olive Branch OLV 142 MS Stennis International HSA 143 MS Tupelo Regional TUP 144 MT Bozeman Yellowstone International BZN 145 MT Glacier Park International GPI 146 MT Missoula International MSO 147 NC Concord Regional JQF 148 NC Hickory Regional HKY 149 NC Kinston Regional Jetport at Stallings Field ISO 150 NC Coastal Carolina Regional EWN 151 NC Smith Reynolds INT 152 ND Minot International MOT 153 NE Central Nebraska Regional GRI 154 NH Boire Field ASH 155 NH Lebanon Muni LEB 156 NJ Trenton Mercer TTN 157 NM Double Eagle II AEG



158 NM Four Corners Regional FMN 159 NM Lea County Regional HOB 160 NM Santa Fe Muni SAF 161 NV Henderson Executive HND 162 NY Francis S. Gabreski FOK 163 NY Niagara Falls International IAG 164 NY Griffiss International RME 165 NY Stewart International SWF 166 NY Ithaca Tompkins Regional ITH 167 OH Burke Lakefront BKL 168 OH Cincinnati Muni Airport Lunken Field LUK 169 OH Bolton Field TZR 170 OH Cuyahoga County CGF 171 OH Ohio State University OSU 172 OK Ardmore Muni ADM 173 OK Enid Woodring Regional WDG 174 OK Lawton-Fort Sill Regional LAW 175 OK Stillwater Regional SWO 176 OK Univ of Oklahoma Westheimer OUN 177 OK Wiley Post PWA 178 OR Aurora State UAO 179 OR Eastern Oregon Regional at Pendleton PDT 180 OR McNary Field SLE 181 OR Rogue Valley International-Medford MFR 182 OR Roberts Field RDM 183 OR Southwest Oregon Regional OTH 184 OR Portland-Troutdale TTD 185 PA Lancaster LNS 186 PA University Park UNV 187 PA Williamsport Regional IPT 188 PA Arnold Palmer Regional LBE 189 PA Capital City CXY 190 PR Fernando Luis Ribas Dominicci SIG 191 PR Rafael Hernandez BQN 192 SC Donaldson Field GYH 193 SC Grand Strand CRE 194 SC Greenville Downtown GMU 195 SC Hilton Head HXD 196 SD Rapid City Regional RAP 197 TN McKeller-Sipes Regional MKL



198 TN Millington Regional Jetport NQA 199 TN Smyrna MQY 200 TX Arlington Municipal GKY 201 TX Brownsville/South Padre Island International BRO 202 TX Denton Enterprise DTO 203 TX Easterwood Field CLL 204 TX Fort Worth-Spinks FWS 205 TX Georgetown Muni GTU 206 TX Grand Prairie Muni GPM 207 TX Laredo International LRD 208 TX Conroe-North Houston Regional CXO 209 TX McAllen Miller International MFE 210 TX McKinney National TKI 211 TX Mesquite Metro HQZ 212 TX New Braunfels Regional BAZ 213 TX Dallas Executive RBD 214 TX Valley International HRL 215 TX San Angelo Regional/Mathis Field SJT 216 TX San Marcos Regional HYI 217 TX Scholes International at Galveston GLS 218 TX Stinson Muni SSF 219 TX Sugar Land Regional SGR 220 TX Tyler Pounds Regional TYR 221 TX Victoria Regional VCT 222 TX TSTC Waco CNW 223 UT Ogden-Hinckley OGD 224 UT Provo Muni PVU 225 VA Charlottesville-Albemarle CHO 226 VA Lynchburg Regional/Preston Glenn Field LYH 227 VI Henry E Rohlsen STX 228 WA Bellingham International BLI 229 WA Felts Field SFF 230 WA Olympia Regional OLM 231 WA Renton Muni RNT 232 WA Tacoma Narrows TIW 233 WA Walla Walla Regional ALW 234 WA Yakima Air Terminal/McAllister Field YKM 235 WI Appleton International ATW 236 WI Central Wisconsin CWA 237 WI Chippewa Valley Regional EAU



238 WI Kenosha Regional ENW 239 WI La Crosse Regional LSE 240 WI Southern Wisconsin Regional JVL 241 WI Lawrence J. Timmerman MWC 242 WI Waukesha County UES 243 WI Wittman Regional OSH 244 WV Greenbrier Valley LWB 245 WV Morgantown Muni-Walter L Bill Hart Field MGW 246 WV Mid-Ohio Valley Regional PKB 247 WV Wheeling Ohio Co HLG 248 WY Jackson Hole JAC

Source: FAA


Exhibit G. List of 103 FAA-Operated Towers Count State Airport Name Tower ID

1 AK Ted Stevens Anchorage International ANC 2 AK Juneau International JNU 3 AK Merrill Field MRI 4 AZ Falcon Field FFZ 5 AZ Grand Canyon National Park GCN 6 AZ Phoenix Deer Valley DVT 7 AZ Ernest A Love Field PRC 8 AZ Scottsdale SDL 9 AZ Tucson International TUS

10 CA Brackett Field POC 11 CA Bob Hope BUR 12 CA Camarillo CMA 13 CA Chino CNO 14 CA Buchanan Field CCR 15 CA San Gabriel Valley EMT 16 CA Gillespie Field SEE 17 CA Hayward Executive HWD 18 CA John Wayne Airport- Orange County SNA 19 CA Livermore Muni LVK 20 CA Long Beach/Daugherty Field LGB 21 CA Monterey Regional MRY 22 CA Montgomery- Gibbs Executive MYF 23 CA Napa County APC 24 CA Metropolitan Oakland International OAK 25 CA Ontario International ONT 26 CA Palm Springs International PSP 27 CA Palo Alto PAO 28 CA McClellan-Palomar CRQ 29 CA Reid-Hillview of Santa Clara County RHV 30 CA Sacramento International SMF 31 CA Norman Y Mineta San Jose International SJC 32 CA Santa Monica Muni SMO 33 CA Charles M Schulz-Sonoma County STS 34 CA Stockton Metropolitan SCK 35 CA Zamperini Field TOA 36 CA Van Nuys VNY 37 CO Centennial APA



38 CO Pueblo Memorial PUB 39 CO Rocky Mountain Metropolitan BJC 40 CT Bradley International BDL 41 DE New Castle ILG 42 FL Fort Lauderdale Executive FXE 43 FL Fort Lauderdale/Hollywood International FLL 44 FL Orlando Executive ORL 45 FL Orlando Sanford International SFB 46 FL Pensacola International PNS 47 FL Sarasota/Bradenton International SRQ 48 FL Treasure Coast International FPR 49 FL St Pete-Clearwater International PIE 50 FL Miami Executive TMB 51 FL Vero Beach Regional VRB 52 GA Columbus CSG 53 GA DeKalb - Peachtree PDK 54 HI Kahului OGG 55 IL Aurora Muni ARR 56 IL Chicago Executive PWK 57 IL St. Louis Downtown CPS 58 IL DuPage DPA 59 IL Chicago Midway International MDW 60 IN Purdue University LAF 61 KY Bowman Field LOU 62 LA Lakefront NEW 63 MA Laurence G Hanscom Field BED 64 MA Nantucket Memorial ACK 65 MD Joint Base Andrews ADW 66 MI Ann Arbor Muni ARB 67 MI Oakland County International PTK 68 MI Cherry Capital TVC 69 MI Willow Run YIP 70 MN Crystal MIC 71 MN Flying Cloud FCM 72 MN St Paul Downtown Holman Field STP 73 MO Charles B Wheeler Downtown MKC 74 MO Spirit of St Louis SUS 75 NE Eppley Airfield OMA 76 NE Lincoln LNK 77 NH Manchester MHT



78 NJ Essex County CDW 79 NJ Morristown Muni MMU 80 NV North Las Vegas VGT 81 NV Reno/Tahoe International RNO 82 NY Republic FRG 83 NY Long Island Mac Arthur ISP 84 NY Hudson Valley Regional POU 85 NY Westchester County HPN 86 OH James M Cox Dayton International DAY 87 OK Richard Lloyd Jones Jr RVS 88 OR Portland-Hillsboro HIO 89 OR Portland International PDX 90 PA Allegheny County AGC 91 PA Northeast Philadelphia PNE 92 PR Luis Munoz Marin International SJU 93 TX Addison ADS 94 TX Fort Worth Alliance AFW 95 TX Jack Brooks Regional BPT 96 TX David Wayne Hooks Memorial DWH 97 TX Fort Worth Meacham International FTW 98 VA Manassas Regional/Harry P Davis Field HEF 99 VA Newport News/Williamsburg International PHF 100 VA Richmond International RIC 101 VI Cyril E King STT 102 WA Boeing Field/King County International BFI 103 WA Snohomish County (Paine Field) PAE

Source: FAA


Exhibit H. Detailed Scope and Methodology This exhibit presents the technical details of our scope and methodology. We present our work in six sections. In the first three sections, we summarize selected related research, describe the ATC towers included in the analyses, and detail our data sources and preparation. In the methodology section, we discuss our use of k-means and hierarchical clustering to sort the selected towers into groups of comparable facilities, and compare the groups produced by the two methods. In the results section, we present the hierarchical clustering findings and tests of the significance of the cost and safety results under both clustering methods. Finally, in the sensitivity analyses section we examine the effects of two specification changes on the groupings and cost comparisons.

1. Related Research Cluster analysis has been widely used to sort observations within datasets when the researcher may not know, or want to impose, classifications. The technique is especially useful when group classification depends on more than a single characteristic. In the transportation literature, Kenneth D. Kuhn used cluster analysis to select “days that are comparable in terms of the conditions faced during air traffic flow management initiative planning.”23 Another study applied cluster analysis to a set of 42 airlines to explore the potential for groupings beyond low-cost and full-service air carriers.24 K-means clustering was also used to find that airport hubs25 fall into more than FAA’s three-tier classification.26

Information supporting the choice of inputs into the analyses in this report came from a 2003 FAA study in which a number of air and ground control staff at very busy towers were interviewed on factors that contributed to complexity levels. The top four factors were high traffic volume, active runway crossings, frequency congestion, and aircraft differing in performance characteristics. Runway configuration was sixth. We accounted for these factors in our cluster analyses.

23 https://daneshyari.com/article/preview/524716.pdf “A methodology for identifying similar days in air traffic flow management initiative planning.” Transportation Research Part C 69 (2016) 1-15. 24 Urban, Marcia, et al. "Airline categorisation by applying the business model canvas and clustering algorithms." Journal of Air Transport Management 71 (2018): 175-192. 25 FAA defines hub airports based on annual enplanements: large hubs handle 1 percent or more on annual U.S. enplanements; medium hubs handle at least 0.25 percent, but less than 1 percent; and small hubs handle at least 0.05 percent, but less than 0.25 percent. 26 https://www.sciencedirect.com/science/article/abs/pii/S0966692313001099 Ryerson, Megan S., and Hyun Kim. "Integrating airline operational practices into passenger airline hub definition." Journal of Transport Geography 31 (2013): 84-93.

https://daneshyari.com/article/preview/524716.pdf

https://www.sciencedirect.com/science/article/abs/pii/S0966692313001099


2. Tower selection We included nearly all FCTs while considering all plausibly comparable FAA towers for fiscal years 2015 through 2018. This time period corresponds with the most recent FCT contract authorization. We excluded from our data set of FCTs 6 towers operated by the National Guard, leaving us with 248.

We filtered the 264 FAA towers to include only towers that FAA classifies as ATC level 8 or below.27 We also excluded FAA towers co-located with terminal radar approach control (TRACON)28 facilities. Because no contract tower is co-located with a TRACON facility, co-located FAA towers are not comparable for staffing or operational purposes. Lastly, since all contract towers operate in Class C or D airspace, we excluded FAA towers that do not operate in Class C or D airspace, and ended up with 103 FAA towers.

3. Data All data in this report covered fiscal years 2015 through 2018. Data on tower handled operation counts were downloaded from FAA’s OPSNET. OPSNET defines and provides counts of five types of aircraft operations—air carrier, air taxi, general aviation, military, and local.29 Over the 4 years in the sample, the 103 FAA towers fitting our selection criteria handled 58 million operations from these categories, while the 248 contract towers handled 60.4 million. Figure H-1 shows the distribution of total operations handled for each tower type.

FAA provided data on operating hours, tower operating costs, runway configurations, and airspace. The runway configurations include single runway, parallel runways, crossing runways, and converging runways. Towers can control aircraft on any of these configurations, or a combination of the three non-single configurations—meaning a tower could have both parallel and crossing runways, but not single and parallel runways.

The OPSNET data was combined with daily operating hours of each tower. Tower operating hours can change with season, day of the week, or Daylight Savings Time. We computed hourly averages using the sum of aircraft handled in each

27 Each FAA facility is classified as a level 4 through 12, based on numerous factors including traffic volume, complexity and sustainability of traffic. The controllers working at higher level facilities receive greater compensation due to the increased level of air traffic volume and complexity. 28 TRACON or Terminal Radar Approach Control facilities house FAA air traffic controllers who use radar displays and radios to control aircraft approaching and departing airports generally within a 30- to 50-mile radius up to 10,000 feet, as well as aircraft that may be flying over that airspace. 29 See table 1 for definitions of these air traffic types.


category over the total hours operated during the 4-year analysis period. Figures H-2 and H-3 show the distributions of hourly operations handled and average daily operating hours by tower type. Towers in the dataset averaged 15.6 hours of operation per day. In addition, 8.3 percent of towers were open 24 hours a day; these towers comprised 25.2 percent of the FAA towers and 1.2 percent of the FCTs. See table H-1 for summary statistics on the inputs used to cluster towers.

Cost and safety data came from requests to FAA. We focused our safety analyses on risk analysis event (RAE) and surface risk analysis event (SRAE) investigation data provided by FAA. We combined these data into a single measure, counting all instances in which an air traffic controller was involved.30 An FAA official characterized these events as having undergone a deeper analysis to determine severity and associated repeatability factors. These deeper analyses mitigate some selection concerns because each event is chosen by staff at a higher level than the controller. Furthermore, more detailed information was available on whether ATC had played a role in these events.

4. Methodology FAA and contract towers differ in a variety of ways, with the simplest being traffic density—or aircraft handled per hour. To allow us to also account for additional factors affecting air traffic control complexity, we used two clustering methods—k-means and hierarchical—to sort FAA and contract towers into groups that were comparable considering three types of characteristics. We grouped towers based on the number of operations of different types of aircraft and type of runway configuration. We did not allow the clustering methods to consider whether a tower was an FCT or FAA tower, so group assignments depended only on tower characteristics.31

K-Means Clustering

The k-means clustering algorithm required us to set the number of clusters, k, and then run an iterative process sorting the observations into k groups. A randomized condition determined the initial allocation of towers across the groups, and the mean or average of each group was then calculated. In the next

30 RAE documentation is required for any occurrences where less than 66 percent of the separation standard is maintained. Documentation of an SRAE occurs when there is less than 6000 feet of separation on a runway between two aircraft or any event in which an aircraft lands or departs from a taxiway or closed runway. 31 The goal of cluster analysis is to ascertain, on the basis of observed characteristics, whether the observations fall into relatively distinct groups. The difficulty of determining the group to which each observation belongs depends on whether the groups are well-separated or somewhat overlapping. For example, clustering methods could include only FAA towers (or FCTs) in a group if they were not comparable to FCTs (FAA towers) in terms of the characteristics considered.


step, observations were assigned to a new group if a distance formula determined that they were closer to another group’s average than they were to their currently assigned group’s average. Group means were recalculated and observations reassigned until no observations changed groups.

Our inputs included both continuous and categorical data. Such mixed data require the use of standardization or special distance metrics in the k-means algorithm. Similar considerations can apply with continuous data when one input to the algorithm is significantly larger in magnitude than the other inputs. We clustered using Gower’s distance measure, which is appropriate for mixed data. We also standardized our data by demeaning each variable and then dividing by its standard deviation to prevent extreme values from exerting outsize influence on the process.

For the k-means approach, we ran the clustering process setting the number of groups, k, to range from 2 to 25. We then applied the elbow method to the results to select the number of clusters or groups to use in the analyses. The elbow method calculates the within-cluster sum of squares (WSS), plots the value of WSS for each k, and identifies the optimal number of clusters as occurring where there is an elbow or bend in the plot. The WSS measures compactness—how similar observations assigned to the same cluster are to each other—and an elbow in the plot indicates that improvements to compactness have slowed. We further informed our choice by substituting two other measures for the WSS in the elbow method—the logarithm of WSS and eta-squared. The latter measures the proportional reduction of the WSS for each cluster solution, k, relative to the total sum of squares (TSS), and is defined as

ηk2 = 1 – (WSS(k)/TSS)

The solution to the k-means algorithm can be sensitive to its starting point. To account for this, we applied the elbow method to results generated using a large number of randomly selected starting points.32 Specifically, we randomly selected 200 non-negative integers as starting points or seeds for the k-means algorithm. For each seed, we implemented the k-means method and calculated the WSS, its logarithm and eta-squared for k = {2, 3, … , 25}. Using this method, we found an elbow at four clusters. Analogous plots for the logarithm of the WSS and eta-squared also each had a kink at four clusters. In addition, we considered the proportional reduction of error (PRE) coefficient, which measures the percentage reduction in WSS when the number of clusters increases from k-1 to k; its plot flattened out after k=4.

32 In doing so, we follow Makles, A. "Stata Tip 110: How to Get the Optimal k-means Cluster Solution." The Stata Journal 12 (2012): 347-351.


Having determined four clusters to be optimal, we conducted further analyses to determine which four cluster groupings to use. We generated 200 grouping solutions for k=4 (one for each seed), and calculated the average number of towers in each group. We then selected the solution whose number of towers for each group was closest to the average. Thirty-four of the 200 solutions had exactly the same minimum distance to the average group size.33 We picked one of the listed solutions for use in the cost and safety comparisons. Summary statistics for the groups in the selected solution can be seen in tables H-2, H-3, and H-4

Hierarchical Clustering

We also clustered towers using agglomerative hierarchical clustering. In hierarchical clustering, towers are folded into increasingly larger groups based on the similarity and dissimilarity of individual observations and groups, measured using specified metrics. We used Ward’s linkage and Gower’s distance measure to accommodate the mixed nature of our data. The merging is tracked in a graph called a dendrogram,34 and once the process is complete, the analyst can “cut” the observations into groups at any of the agglomerative steps. The height of each vertical line in the dendrogram of the clustering process corresponds to a dissimilarity measure, with a larger vertical distance implying greater dissimilarity. We cut the process at the level below which increases in dissimilarity dropped. This produced four groups or clusters. Tables H-5, H-6, and H-7 report summary statistics for the groups overall and by tower type.

We note that the hierarchical method clusters more strongly on runway configuration than on traffic density, compared to the k-means method. However, both methods grouped towers with single runways together. In both cases, this group consisted of 12 FAA-staffed towers and 71 FCTs that averaged nearly 14 operations per hour. While relationships between the other groups produced by the two methods are not as obvious, table H-8 indicates considerable overlap between them. It shows the distribution of towers across groupings. Each number on the diagonal indicates the number of towers that were sorted into the same group under the two methods. For example, table H-8 reports that 28 towers were sorted into Group 1 under both methods. The off-diagonal numbers track the towers which the two methods sorted into different

33 We considered both Euclidean and Chebyshev’s distance functions, where each group is a “coordinate.” For example, if the number of towers in groups 1 through 4 is (25, 50, 75, 100) for a candidate solution and the group means across the two hundred solutions are (30, 40, 60, 105), the Chebyshev distance is the maximum difference between a group’s size and its mean (in this case, it is 15 = 75-60). 34 A dendrogram is a tree diagram that links all observations according to the hierarchical clustering criteria. Observations linked lower on the dendrogram are more similar to each other than those linked higher up. Larger vertical distances on the figure represent more dissimilarity from one linkage to the next. Horizontal differences do not have an interpretation or meaning.


groups. For example, 17 towers were sorted into Group 1 by the k-means method that the hierarchical clustering sorted into Group 3.

5. Results After creating the groups, we compared the costs and safety of FCT and FAA towers within each group. In this section, we discuss the statistical assessment of the comparisons, and present the hierarchical clustering results.

Cost Comparisons

Using hierarchical clustering, we again found that FCTs had lower costs per aircraft handled than comparable FAA towers, as shown in table H-12. In addition, the range of cost differences within groups was similar using both k-means and hierarchical clustering methods. We tested the statistical significance of the cost differences per aircraft using a pooled t-test within each group under both clustering methods, and consistently found FAA tower costs were statistically greater than FCTs’ costs at the 5 percent significance level. The test results were the same whether we assumed equal or unequal variance of costs.

Safety Comparisons

The annual average safety event numbers in the hierarchical groups appear to be affected by outliers. Table H-13 shows a strikingly large number of annual average safety events for Group 1 FAA towers, and a high rate of such events for Group 1 FCTs. In contrast, the incidence of reported safety events over the analysis period as a whole is lower for FCTs than FAA towers.

We tested the statistical significance of the differences in total reported safety events over fiscal years 2015 through 2018 using Poisson regression with a variable representing exposure to the number of aircraft operations handled by each tower.35 The dependent variable was the sum total of SRAE and RAE events over the analysis period, while the independent variable was an indicator variable that equaled 1 if a tower was a contract tower. For all groups under both clustering methods, the FCT coefficient was negative and significant at the 5 percent level.

We also used two alternative methods to assess the comparison. The first was weighted linear regression, where the dependent variable was the number of events per 100,000 aircraft handled, and the weights were counts of aircraft handled. The second was logit regression, where the dependent variable was an

35 An exposure variable, in this context, consists of a covariate whose logarithm is used in regression with coefficient fixed at 1. In count regression models, exposure variables ensure that observations are comparable in their unit of measurement.


indicator variable that equals 1 if a tower had no safety risk events and the controls were the FCT dummy variable and the logarithm of aircraft handled. The weighted regression confirmed the results of the Poisson regression. The logit regression revealed that in all cases, FCTs were statistically more likely to have had no safety risk events, even when controlling for the number of aircraft handled.

6. Sensitivity Analyses We performed two sensitivity analyses on both the k-means and hierarchical clustering. In the first, we added a measure of traffic density on the ninetieth percentile busiest day of operations—a measure FAA uses to ensure that it has sufficient staff at each tower.36 For the second, we reduced the number of runway configuration categories considered to two—single runway and other. We followed the same steps detailed in exhibit A to generate groupings under the new specifications.37

The addition of the traffic density measure changed the clusters produced using the k-means method to a limited extent, and had no impact on hierarchical method groupings. Table H-9 shows that in the k-means case 83.2 percent of towers fell into the same groups as in the original analysis.

The reduction in the runway configuration categories changed the groupings so that 66.4 percent, under the k-means method, and 63.8 percent, under the hierarchical method, ended up in the same groups as in the original analyses, as indicated in tables H-10 and H-11. The k-means clustering now concentrates carrier operations in one group—which includes five FCTs, as shown in tables H-16 and H-17. Under the hierarchical method, the optimal number of clusters drops to three. The “other’ runway towers with low carrier traffic, which had been split between two groups in the original analysis, are now mainly gathered into a single group. Tables H-18 and H-19 report statistics for the new hierarchical method clusters. Recalculating comparative labor costs using the new groupings, we found a similar range of differences in costs between the two tower types as we found earlier. Tables H-14 and H-15 report these results.

36 The ninetieth percentile busiest day is defined by sorting all days based on tower operations and choosing the day with operations busier than 90 percent but less than 10 percent of all the other days in the analysis period. The number of aircraft handled on that day is used to calculate traffic density instead of an average for all days for this alternative analysis. 37 The selected grouping for each specification under the k-means clustering used a different seed.


Table H-1. Summary Statistics of Inputs into the Clustering Algorithms

1. Aircraft Type Handled Average Standard Deviation Min Max Carrier 25551.81 94093.12 0 914102 General Aviation 137946.2 106812.2 13147 637552 Taxi 38930.11 57921.51 4 403933 Military 17622.29 35961.62 186 363009 Local Civil 117260.6 133922.5 0 967342 Aircraft Handled Total 337311.1 254101.6 26833 1542924 2. FAA Aircraft Type Handled Average Standard Deviation Min Max Carrier 74023.91 162798.1 2 914102 General Aviation 218660.4 135228.7 13147 637552 Taxi 66292.53 81237.03 1804 403933 Military 16387.26 44771.62 555 363009 Local Civil 187854.9 184622.4 0 967342 Aircraft Handled Total 563219 306971.4 86552 1542924 3. FCT Aircraft Type Handled Average Standard Deviation Min Max Carrier 5420.254 14633.1 0 114114 General Aviation 104423.8 69063.51 15519 347718 Taxi 27565.88 39834 4 311408 Military 18135.22 31683.67 186 222974 Local Civil 87941.25 91636.59 486 570656 Aircraft Handled Total 243486.4 149863.1 26833 1055970

4. Runway Configuration Total Proportion Of Towers FAA FCT Single 83 0.24 12 71 Parallel 89 0.25 55 34 Crossing 200 0.57 60 140 Converging 73 0.21 25 48


Table H-2. Tower Groupings – K-Means

Group FAA FCT

1 29 17

2 17 44

3 12 71

4 45 116

Total 103 248


Table H-3. K-Means Groups Summary Statistics

Group Aircraft Operations per Tower per Hour Runway Configuration

Group 1 Total Carrier General Aviation Taxi Military Local Civil Single Parallel Crossing Converging

Average 22.46 2.82 8.27 2.40 0.96 8.00 0.00 1.00 0.00 0.26

Std Dev 5.66 5.66 2.91 1.72 8.23 0.00 0.00 0.00 0.44

Minimum 0.000 0.69 0.05 0.03 0.00 0.00 1.00 1.00 0.00

Maximum 26.07 27.27 15.07 8.22 36.78 0.00 1.00 0.00 1.00


Average 14.66 0.97 5.70 1.68 1.00 5.32 0.00 0.25 0.64 1.00

Std Dev 2.94 3.96 2.37 1.64 6.36 0.00 0.43 0.48 0.00

Min 0.00 1.21 0.00 0.01 0.01 0.00 0.00 0.00 1.00

Max 20.42 18.38 13.40 8.24 29.34 0.00 1.00 1.00 1.00


Average 13.77 0.38 6.18 1.66 0.66 4.88 1.00 0.00 0.00 0.00

Std Dev 0.82 4.67 2.92 0.96 4.83 0.00 0.00 0.00 0.00

Min 0.00 0.71 0.02 0.01 0.01 1.00 0.00 0.00 0.00

Max 4.92 25.29 21.82 3.98 18.94 1.00 0.00 0.00 0.00


Average 13.03 0.50 5.65 1.42 0.70 4.75 0.00 0.17 1.00 0.00

Std Dev 1.98 4.09 2.10 1.68 5.25 0.00 0.38 0.00 0.00

Min 0.00 0.67 0.00 0.01 0.00 0.00 0.00 1.00 0.00

Max 21.21 20.84 14.66 15.53 28.16 0.00 1.00 1.00 0.00


Table H-4. K-Means Groups Operations per Tower per Hour and Runway Configurations by Tower Type

Group 1 FCT Carrier General Aviation Taxi Military Local Civil Single Parallel Crossing Converging

Average 0.25 5.85 2.51 1.53 5.99 0.00 1.00 0.00 0.24

Std Dev 0.47 4.31 3.62 2.27 7.13 0.00 0.00 0.00 0.44

Min 0.00 1.45 0.05 0.03 0.26 0.00 1.00 0.00 0.00

Max 1.61 14.89 15.07 8.22 25.07 0.00 1.00 0.00 1.00

FAA Carrier General Aviation Taxi Military Local Civil Single Parallel Crossing Converging

Average 4.34 9.69 2.34 0.62 9.19 0.00 1.00 0.00 0.28

Std Dev 6.71 5.94 2.47 1.23 8.71 0.00 0.00 0.00 0.45

Min 0.00 0.69 0.10 0.03 0.00 0.00 1.00 0.00 0.00

Max 26.07 27.27 10.65 6.19 36.78 0.00 1.00 0.00 1.00


Average 0.31 5.33 1.30 1.16 4.83 0.00 0.14 0.55 1.00

Std Dev 0.76 3.60 2.10 1.86 5.14 0.00 0.35 0.50 0.00

Min 0.00 1.21 0.00 0.01 0.21 0.00 0.00 0.00 1.00

Max 4.60 16.36 13.40 8.24 27.19 0.00 1.00 1.00 1.00


Average 2.68 6.65 2.64 0.59 6.57 0.00 0.53 0.88 1.00

Std Dev 5.16 4.74 2.80 0.71 8.86 0.00 0.51 0.33 0.00

Min 0.00 1.32 0.59 0.04 0.01 0.00 0.00 0.00 1.00

Max 20.42 18.38 10.68 2.47 29.34 0.00 1.00 1.00 1.00



Average 0.37 5.15 1.17 0.74 4.34 1.00 0.00 0.00 0.00

Std Dev 0.85 3.13 1.16 1.02 4.30 0.00 0.00 0.00 0.00

Min 0.00 0.77 0.02 0.01 0.01 1.00 0.00 0.00 0.00

Max 4.92 14.10 5.53 3.98 16.81 1.00 0.00 0.00 0.00


Average 0.44 12.27 4.60 0.22 8.07 1.00 0.00 0.00 0.00

Std Dev 0.66 7.28 6.62 0.26 6.55 0.00 0.00 0.00 0.00

Min 0.00 0.71 0.10 0.05 0.21 1.00 0.00 0.00 0.00

Max 1.69 25.29 21.82 1.01 18.94 1.00 0.00 0.00 0.00


Average 0.11 4.55 1.15 0.69 3.55 0.00 0.09 1.00 0.00

Std Dev 0.25 3.08 1.68 1.29 3.45 0.00 0.29 0.00 0.00

Min 0.00 0.67 0.00 0.01 0.14 0.00 0.00 1.00 0.00

Max 1.36 16.64 10.57 9.55 21.28 0.00 1.00 1.00 0.00


Average 1.50 8.50 2.11 0.74 7.84 0.00 0.38 1.00 0.00

Std Dev 3.56 4.96 2.82 2.43 7.45 0.00 0.49 0.00 0.00

Min 0.00 1.60 0.10 0.02 0.00 0.00 0.00 1.00 0.00

Max 21.21 20.84 14.66 15.53 28.16 0.00 1.00 1.00 0.00


Table H-5. Tower Groupings - Hierarchical

Group FAA FCT

1 55 34

2 12 71

3 8 38

4 28 105

Total 103 248


Table H-6. Hierarchical Groups Summary Statistics

Group Aircraft Operations Handled by Tower per Hour Runway Configuration


Average 22.29 2.26 8.11 2.06 1.08 8.78 0.00 1.00 0.48 0.30

Std Dev 5.14 5.59 2.67 2.32 8.55 0.00 0.00 0.50 0.46

Minimum 0.00 0.69 0.00 0.03 0.00 0.00 1.00 0.00 0.00

Maximum 26.07 27.27 15.07 15.53 36.78 0.00 1.00 1.00 1.00


Average 13.77 0.38 6.18 1.66 0.66 4.88 1.00 0.00 0.00 0.00

Std Dev 0.82 4.67 2.92 0.96 4.83 0.00 0.00 0.00 0.00

Min 0.00 0.71 0.02 0.01 0.01 1.00 0.00 0.00 0.00

Max 4.92 25.29 21.82 3.98 18.94 1.00 0.00 0.00 0.00


Average 12.37 0.66 5.07 1.67 1.09 3.88 0.00 0.00 0.52 1.00

Std Dev 1.67 3.21 2.67 1.70 4.02 0.00 0.00 0.51 0.00

Min 0.00 1.21 0.00 0.01 0.01 0.00 0.00 0.00 1.00

Max 7.53 12.05 13.40 8.24 18.15 0.00 0.00 1.00 1.00


Average 11.07 0.29 5.14 1.36 0.54 3.74 0.00 0.00 1.00 0.00

Std Dev 0.96 3.45 1.92 0.98 3.50 0.00 0.00 0.00 0.00

Min 0.00 0.67 0.00 0.01 0.14 0.00 0.00 1.00 0.00

Max 8.55 17.25 11.14 8.05 21.28 0.00 0.00 1.00 0.00


Table H-7. Hierarchical Groups Operations per Tower per Hour and Runway Configurations by Tower Type


Average 0.25 5.39 1.94 1.58 6.00 0.00 1.00 0.50 0.29

Std Dev 0.46 3.96 2.77 2.39 6.59 0.00 0.00 0.51 0.46

Max 0.00 1.06 0.00 0.03 0.26 0.00 1.00 0.00 0.00

Min 1.68 16.36 15.07 9.55 27.19 0.00 1.00 1.00 1.00


Average 3.49 9.80 2.14 0.77 10.50 0.00 1.00 0.47 0.31

Std Dev 6.23 5.81 2.63 2.24 9.21 0.00 0.00 0.50 0.47

Max 0.00 0.69 0.10 0.03 0.00 0.00 1.00 0.00 0.00

Min 26.07 27.27 14.66 15.53 36.78 0.00 1.00 1.00 1.00


Average 0.37 5.15 1.17 0.74 4.34 1.00 0.00 0.00 0.00

Std Dev 0.85 3.13 1.16 1.02 4.30 0.00 0.00 0.00 0.00

Max 0.00 0.77 0.02 0.01 0.01 1.00 0.00 0.00 0.00

Min 4.92 14.10 5.53 3.98 16.81 1.00 0.00 0.00 0.00


Average 0.44 12.27 4.60 0.22 8.07 1.00 0.00 0.00 0.00

Std Dev 0.66 7.28 6.62 0.26 6.55 0.00 0.00 0.00 0.00

Max 0.00 0.71 0.10 0.05 0.21 1.00 0.00 0.00 0.00

Min 1.69 25.29 21.82 1.01 18.94 1.00 0.00 0.00 0.00



Average 0.29 5.14 1.19 1.16 4.24 0.00 0.00 0.47 1.00

Std Dev 0.78 3.32 2.20 1.85 4.08 0.00 0.00 0.51 0.00

Max 0.00 1.21 0.00 0.01 0.21 0.00 0.00 0.00 1.00

Min 4.60 12.05 13.40 8.24 18.15 0.00 0.00 1.00 1.00


Average 2.38 4.71 3.97 0.79 2.16 0.00 0.00 0.75 1.00

Std Dev 3.25 2.74 3.59 0.60 3.42 0.00 0.00 0.46 0.00

Max 0.03 1.92 1.25 0.13 0.01 0.00 0.00 0.00 1.00

Min 7.53 10.56 10.68 1.96 10.27 0.00 0.00 1.00 1.00


Average 0.11 4.60 1.17 0.56 3.44 0.00 0.00 1.00 0.00

Std Dev 0.24 3.16 1.71 0.94 3.43 0.00 0.00 0.00 0.00

Max 0.00 0.67 0.00 0.01 0.14 0.00 0.00 1.00 0.00

Min 1.36 16.64 10.57 8.05 21.28 0.00 0.00 1.00 0.00


Average 0.98 7.15 2.09 0.45 4.87 0.00 0.00 1.00 0.00

Std Dev 1.92 3.82 2.45 1.15 3.58 0.00 0.00 0.00 0.00

Max 0.00 1.60 0.17 0.02 0.32 0.00 0.00 1.00 0.00

Min 8.55 17.25 11.14 5.19 16.28 0.00 0.00 1.00 0.00


Table H-8. Comparison K-Means and Hierarchical Clusters

Note: Each count on a diagonal is the number of towers sorted into the same group under both methods. Percent of all towers in the same groups is 87.7. Group numbering is not aligned across appendix tables.

Table H-9. Comparison K-Means Clusters With and Without 90th Percentile Day Traffic Density38

Note: Each count on a diagonal is the number of towers sorted into the same group under both methods. Percent of all towers in the same groups is 83.2. Group numbering is not aligned across the tables in exhibit H.

38 See footnote 36 for an explanation of ninetieth percentile day traffic density.


Table H-10. Comparison K-Means Clusters with Two Runway Configuration Categories

Note: Each count on a diagonal is the number of towers sorted into the same group under both methods. Percent of all towers in the same groups is 66.4 Group numbering is not aligned across the tables in exhibit H.

Table H-11. Comparison Hierarchical Clusters with Two Runway Configuration Categories

Note: Each count on a diagonal is the number of towers sorted into the same group under both methods. Percent of all towers in the same groups is 63.8 Group numbering is not aligned across the tables in exhibit H.


Table H-12. Cost Comparisons by Hierarchical Groups



Average FAA labor and benefits cost per aircraft handled $21.66 $19.93 $36.87 $27.62

Average total contract tower labor and benefits $2,648,566.54 $2,304,554.78 $2,336,412.68 $2,293,368.56

Average contract tower labor cost per aircraft handled $7.84 $9.48 $9.09 $11.01


Table H-13. Summary of Risk Analysis and Surface Risk Analysis Events involving an Air Traffic Controller for Hierarchical Groups

Aircraft Handled and Events Group 1 Group 2 Group 3 Group 4

FAA average aircraft handled per year 171,670 135,711 96,501 95,019

FCT average aircraft handled per year 84,472 60,778 64,257 52,068

Average number of risk analysis and surface risk analysis events involving air traffic controllers per million aircraft handled at FAA towers

8.71 7.37 8.42 7.05

Average number of risk analysis and surface risk analysis events involving air traffic controllers per million aircraft handled at FCTs

1.83 0.52 0.92 1.19

Total risk analysis and surface risk analysis events involving air traffic controllers per million aircraft handled 7.11 2.40 2.72 3.11


Table H-14. Cost Comparisons for K-Means Groups Using Two Runway Configuration Categories



Average FAA labor and benefits cost per aircraft handled $16.86 $29.90 $19.93 $30.63

Average total contract tower labor $3,073,880.06 $3,081,336.05 $2,304,554.78 $2,270,812.92

Average contract tower labor cost per aircraft handled $5.24 $8.95 $9.48 $11.20


Table H-15. Cost Comparisons for Hierarchical Groups Using Two Runway Configuration Categories

Costs Group 1 Group 2 Group 3

Average total FAA labor and benefits $12,332,596.48 $10,817,413.79 $14,742,452.29

Average labor and benefits cost per aircraft handled $18.99 $19.93 $31.18

Average total contract tower labor $2,779,594.07 $2,304,554.78 $2,231,491.74

Average contract tower labor cost per aircraft handled $6.41 $9.48 $12.47

Average percent fewer resources used by comparable contract towers 66.23% 52.4% 60.013%


Table H-16. Tower Groupings – K-Means Using Two Runway Configuration Categories

Group FAA FCT

1 32 17

2 14 5

3 12 71

4 45 155

Total 103 248


Table H-17. Means Groups Generated Using Two Runway Configuration Categories

Group Aircraft Operations Handled by Tower per Hour Runway Configuration Group 1 Total Carrier Gen Av Taxi Military Local Civil Single Parallel Crossing Converging Average 31.23 0.80 13.56 1.59 0.31 14.98 0.00 0.61 0.61 0.35

Std Dev 2.55 3.92 1.86 0.54 7.47 0.00 0.49 0.49 0.48 Minimum 0.00 7.35 0.00 0.01 4.32 0.00 0.00 0.00 0.00 Maximum 14.85 27.27 10.65 3.37 36.78 0.00 1.00 1.00 1.00

Group 2 Total Carrier Gen Av Taxi Military Local Civil Single Parallel Crossing Converging Average 23.12 8.52 4.50 7.51 0.26 2.32 0.00 0.53 0.53 0.42

Std Dev 8.04 3.06 4.54 0.21 6.34 0.00 0.51 0.51 0.51 Min 0.01 0.92 1.42 0.03 0.00 0.00 0.00 0.00 0.00 Max 26.07 12.89 15.07 0.76 28.10 0.00 1.00 1.00 1.00


Std Dev 0.82 4.67 2.92 0.96 4.83 0.00 0.00 0.00 0.00 Min 0.00 0.71 0.02 0.01 0.01 1.00 0.00 0.00 0.00 Max 4.92 25.29 21.82 3.98 18.94 1.00 0.00 0.00 0.00


Std Dev 0.85 2.34 1.03 1.89 2.64 0.00 0.43 0.40 0.43 Min 0.00 0.67 0.00 0.01 0.09 0.00 0.00 0.00 0.00 Max 5.40 11.93 5.46 15.53 11.14 0.00 1.00 1.00 1.00


Table H-18. Tower Groupings – Hierarchical Using Two Runway Configurations

Group FAA FCT

1 48 45

2 12 71

3 43 132

Total 103 248


Table H-19. Hierarchical Groups Generated Using Two Runway Configuration Categories

Group Aircraft Operations Handled by Tower per Hour Runway Configuration

Group 1 Total Carrier Gen Av Taxi Military Local Civil Single Parallel Crossing Converging

Average 23.94 0.62 10.76 1.36 0.41 10.80 0.00 0.48 0.69 0.28

Std Dev

1.97 4.26 1.44 0.64 6.84 0.00 0.50 0.47 0.45

Minimum

0.00 3.49 0.00 0.01 2.56 0.00 0.00 0.00 0.00

Maximum 14.85 27.27 8.96 3.37 36.78 0.00 1.00 1.00 1.00


Average 13.77 0.38 6.18 1.66 0.66 4.88 1.00 0.00 0.00 0.00

Std Dev

0.82 4.67 2.92 0.96 4.83 0.00 0.00 0.00 0.00

Min

0.00 0.71 0.02 0.01 0.01 1.00 0.00 0.00 0.00

Max 4.92 25.29 21.82 3.98 18.94 1.00 0.00 0.00 0.00


Average 10.28 1.21 3.65 1.80 1.03 2.59 0.00 0.25 0.78 0.27

Std Dev

3.72 1.83 2.69 1.99 3.27 0.00 0.44 0.42 0.44

Min

0.00 0.67 0.00 0.01 0.00 0.00 0.00 0.00 0.00

Max 26.07 10.16 15.07 15.53 28.10 0.00 1.00 1.00 1.00


Figure H-1. Distribution of Total Aircraft Handled by Tower Type for Fiscal Years 2015-2018 (An accessible version of this information is presented below.)


Figure H-2. Distribution of Hourly Aircraft Handled by Tower Type, Fiscal Years 2015-2018 (An accessible version of this information is presented below.)


Figure H-3. Average Daily Operating Hours by Tower Type, Fiscal Years 2015-2018

Exhibit I. Major Contributors to This Report 65

Exhibit I. Major Contributors to This Report NELDA SMITH PROGRAM DIRECTOR

TASHA THOMAS PROJECT MANAGER

ALEX ROMERO SENIOR ANALYST

SEAN WOODS SENIOR AUDITOR

ROSE STEVENS SENIOR ANALYST

TEKLAY LEGESE AUDITOR

BETTY KRIER CHIEF ECONOMIST

JERROD SHARPE SENIOR ECONOMIST

JOAO MACIEIRA SENIOR ECONOMIST

EVAN ROGERS ECONOMIST

PETRA SWARTZLANDER SENIOR STATISTICIAN

SUSAN NEILL WRITER-EDITOR

SETH KAUFMAN SENIOR COUNSEL

CELESTE BORJAS ASSOCIATE COUNSEL

CHRISTINA LEE VISUAL COMMUNICATIONS SPECIALIST

Our Mission OIG conducts audits and investigations on

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