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Federal AviationAdministration

The Human Element in Actual Communication Performance (ACP)

Presented to: PBCS Workshop

By: Kim Cardosi, [email protected]

Date: 17-19 June 2015

Human Element in ACP

17-19 June 20152Federal Aviation

Administration

The Human Element in Actual Communication Performance (ACP)

• What is it?

• How do we measure it?

• What affects it?

• What can be done to protect against known errors?



Administration

Data Link Performance Monitoring• The ICAO Global Plan calls for the implementation of a

performance based system and ICAO Annex 11 requires that data link system performance is monitored to verify that an acceptable level of safety continues to be met.

• The Performance-based Communication and Surveillance Manual (Doc 9869) provides guidance material on the required data points and how to calculate the actual communication performance (ACP), actual communication technical performance (ACTP), pilot operational response time (PORT). – This guidance was formerly contained in Global Operational Data

Link Document (GOLD)



Administration

ACP

Up Down

Sent) (UplinkReceived) (WILCOACP Required Communication Monitored Performance (RCMP)

∆Down

2∆UpACTP Required Communication

Technical Performance (RCTP)

ACTPACPPORT RCP Pilot Operational Response Time (PORT)

1 Uplink Sent Date/time ATSU sent CPDLC clearance to the aircraft2 MAS Received Date/time ATSU receives the MAS for the CPDLC clearance3 WILCO Sent Date/time aircraft sends WILCO response for the CPDLC clearance4 WILCO Received Date/time ATSU receives WILCO response for the CPDLC clearance

1 42 3

The measurements (in seconds) are calculated as follows:



Administration

Factors influencing ACP

• Equipment– Some indications of an ATC message are more efficient at

attracting attention than others.

– Time required to access the message depends on the flight deck interface.

• Airline procedures/training – Speed/accuracy tradeoff

• Clearances – and combination of clearances– Pilots respond faster and more accurately to some clearances

compared to others.



Administration

ZNY Sample of ACP - Specification: RCP 240 95% benchmark

January 1, 2013 to June 30, 2013 (6 months) - 3 most common messagesMessage Count ACP <=180 sec ACTP <=120 sec PORT <=60 sec

CLIMB TO REACH (level) BY (time); REPORT MAINTAINING (level)U26 U129 11,231 99.2% 99.6% 96.5%

CLIMB TO (level); REPORT MAINTAINING (level)U20 U129 8,801 99.2% 99.7% 97.3%

MAINTAIN (speed)U106 1,902 99.2% 99.5% 98.5%



Administration

PORT Varies By Message Type (1 of 2) Message Count PORT < 60 sec

CLIMB TO (level); REPORT MAINTAINING (level)U20 U129 8,801 97.3%

REPORT MAINTAINING (level); CLIMB TO (level)U129 U20 706 97.5%

REPORT MAINTAINING (level); CLIMB TO REACH (level) BY (time)U129 U26 860 96.1%

CLIMB TO REACH (level) BY (time); REPORT MAINTAINING (level); Due to Traffic

U26 U129 U166 732 94.0%

Due to Traffic; MAINTAIN (level); AT (time) CLIMB TO (level); CLIMB TO REACH (level) BY (time); MAINTAIN (speed) OR LESSU166 U19 U21 U26 U129 109 83.5%



Administration

PORT Varies By Message Type (2 of 2)

Message Count PORT < 60 sec

CLIMB TO REACH (level) BY (time); REPORT MAINTAINING (level)U26 U129 11,231 96.5%

CLIMB TO REACH (level) BY (time); REPORT MAINTAINING (level); WHEN CAN YOU ACCEPT (level)

U26 U129 U148 220 69.1%

CLIMB TO (level); REPORT MAINTAINING (level)U20 U129 8,801 97.3%

CLIMB TO (level); REPORT MAINTAINING (level);WHEN CAN YOU ACCEPT (level)

U20 U129 U148 181 68.5%



Administration

What’s known about pilot error?

• Few studies on the nature of pilot error associated with data link based on operational data.

• Data entry errors are to be expected.

• Conditional clearances have long been regarded as problematic.

Federal AviationAdministrationFAA Study on

Conditional Clearances



Administration

What is a conditional clearance?• A vertical clearance that includes a restriction, such as

– a time or place for starting the climb or descent– a time or place for when the level is to be reached

Ref Conditional clearance message elementMessage element with “AT” restriction

UM21 AT [time] CLIMB TO [level] or AT [time] CLIMB TO AND MAINTAIN [altitude]UM22 AT [position] CLIMB TO [level] or AT [position] CLIMB TO AND MAINTAIN [altitude]UM24 AT [time] DESCEND TO [level] or AT [time] DESCEND TO AND MAINTAIN [altitude]UM25 AT [position] DESCEND TO [level] or AT [position] DESCEND TO AND MAINTAIN [altitude]

Message element with “BY” restrictionUM26 CLIMB TO REACH [level] BY [time]UM27 CLIMB TO REACH [level] BY [position]UM28 DESCEND TO REACH [level] BY [time]UM29 DESCEND TO REACH [level] BY [position]

Note.— Message elements shown in bold text indicate the preferred choice, per Doc 4444, and should be used for new implementations. The second choice is shown in italic text and indicates legacy implementations (e.g. most FANS 1/A aircraft) that are considered acceptable (GOLD, Appendix A).



Administration

Conditional Clearances – identified issues

– “AT TIME/POSITION…” – pilots can miss the condition and act immediately or forget to comply when condition is met.

• Most often act immediately – especially when clearance follows a request for a climb

– CLIMB/DESCEND to level BY TIME/POSITION –has been misunderstood (relatively few cases)

• BY – misinterpreted as by way of, or initiation (as opposed to completion) of maneuver



Administration

Doc 4444 Appendix 5 – Proposed Changes

Current Doc 4444 Proposed 2016

Ref Message element Message element

Message element with restriction for starting a climb or descent

UM21 AT [time] CLIMB TO [level] AT TIME [time] CLIMB TO [level]

UM24 AT [time] DESCEND TO [level] AT TIME [time] DESCEND TO [level]

Message element with restriction for when a level is to be reached

UM26 CLIMB TO REACH [level] BY [time]CLIMB TO REACH [level single] BEFORE TIME [time]

UM27 CLIMB TO REACH [level] BY [position]

CLIMB TO REACH [level single] BEFORE PASSING [position]

UM28 DESCEND TO REACH [level] BY [time]

DESCEND TO REACH [level single] BEFORE TIME [time]

UM29 DESCEND TO REACH [level] BY [position]

DESCEND TO REACH [level single] BEFORE PASSING [position]

Per RTCA SC-214 / EUROCAE WG-78



Administration

Use of conditional clearances

• KZWY – 20-25% of operational communication are conditional clearances

• In comparison, about 5 times more than KZAK; more than 10 times more than PAZA

KZWY KZAK PAZA2010 2011 2012 2010 2011 2012 2010 2011 2012

% DL CCs of all DL Transactions 23.1% 21.1% 19.1% 2.9% 3.1% 3.1% 1.4% 2.2% 1.8%

% V CCs of all V Transactions 26.7% 25.2% 23.8% 5.0% 5.3% 6.0% 1.2% 1.4% 1.3%



Administration

Conditional Clearance LHDs

• Large height deviations (LHDs) in which the restriction in a conditional clearance was a causal factor

• Focus – New York– Data are more readily available

– Conditional clearance LHDs can be correlated to the NAT vertical risk

• Evaluated data mostly for the period 2009 to 2012– Estimated error rates for conditional clearance LHDs



Administration

KZWY conditional clearance LHDs

• Message use –“BYs” 10 times more common than “ATs”

• CC LHDs – The “ATs” (UM2126) dominate

0

4

8

12

16

20

UM

2126

UM

2428

UM

2429

UM

21

UM

26

UM

27

UM

28

UM

29

CC-AT CC-BY

CC

LH

D C

NT

V-CC LHD CNT - KZWY WATRSV-CC LHD CNT - KZWY NATDL-CC LHD CNT - KZWY WATRSDL-CC LHD CNT - KZWY NAT

020406080

100120

UM

2126

UM

2428

UM

2429

UM

21

UM

26

UM

27

UM

28

UM

29

CC-AT CC-BYC

C L

HD

TA

WL

(min

utes

)

V-CC LHD TAWL - KZWY WATRSV-CC LHD TAWL - KZWY NATDL-CC LHD TAWL - KZWY WATRSDL-CC LHD TAWL - KZWY NAT

New York (KZWY) CNT - 35 New York (KZWY) TAWL - 200 minutes

By message type



Administration

KZWY conditional clearance LHDs

• Increasing trend in conditional clearance LHDs associated with UM2126; decrease with UM26

0

1

2

3

4

5

6

7

8

9

2009 2010 2011 2012 2009 2010 2011 2012

CC-AT CC-BY

CC

LH

D C

NT

V-UM29

V-UM28

V-UM26

DL-UM29

DL-UM28

DL-UM26

V-UM2429

V-UM2428

V-UM2126

DL-UM21

DL-UM2126

0

10

20

30

40

50

60

2009 2010 2011 2012 2009 2010 2011 2012

CC-AT CC-BY

CC

LH

D T

AW

L (m

inut

es)

V-UM29

V-UM28

V-UM26

DL-UM29

DL-UM28

DL-UM26

V-UM2429

V-UM2428

V-UM2126

DL-UM21

DL-UM2126

New York (KZWY) CNT - 35 New York (KZWY) TAWL - 200 minutes

By message type and by year



Administration

Error rate forconditional clearance LHDs

Message type

CPDLC (DL)

Voice (V)

Message type

CPDLC (DL)

Voice (V)

CC-AT 16 4 UM2126 22 3.4

CC-BY 0.7 0.3 UM26 w/o UM21 0.6 0.2

0.

5.

10

15

20

25

2009 to 2012

Erro

r rat

e(b

y m

sg ty

pe)

(per

10,

000

msg

s)

KZWY DL Total CC-AT

V Total CC-AT

DL UM2126

V UM2126

DL Total CC-BY

V Total CC-BY

DL UM26 w/o UM21

V UM26 w/o UM21



Administration

Contributory factors –what we learned

• Fewer cases of forgetting to comply with AT than expected; few cases missing BY

• Errors involving ‘native English’ carriers as prevalent as non-native English carriers

• Aircraft type/display type not a factor in errors associated with UM2126 LHDs

• ATC seldom issues CLR with the AT restriction; ATC issues CLR with the BY restriction 10 times more (which sets pilot expectation)

• Flight crew misses AT restriction, regardless of whether or not it is in response to a flight crew request or negotiation

• UM26 overshadows UM21; BY is the compelling factor

• PORT for UM 21+ UM 26 (U19 U21 U26 U129) - 90.5% of PORT < 60 indicates that its unlikely that GOLD procedure was followed.



Administration

Recommendations (1 of 4)

• Aircraft manufacturers and equipment suppliers should consider avionics functionality that alerts the flight crew for conditional clearances containing the AT restriction when:

– It is time for the flight crew to execute the maneuver after meeting a condition; or

– The flight crew is executing a maneuver and the condition has not been met.

– Is being implemented in some modern aircraft.



Administration


• Standardize controller procedures: (see GOLD)

– Order of message elements should be standardized (predictable)

– Use of multi-element messages – only messages that are dependent should be sent in the same message; WHEN CAN YOU ACCEPT (level) should be sent separately

– In response to requests or following level negotiations (e.g., response should issue same level as requested; conditional clearances should be preceded by UNABLE)

– Use of ADS-C reports to determine the level of aircraft; this eliminates the need to request level reports as part of a conditional clearance in ADS-C environments

– Minimize use of “dual restriction” conditional clearances, e.g., UM2126



Administration


• Flight crew procedures– Each crewmember should silently and individually

read each CPDLC message and then confer, whenever feasible, and at a minimum, before execution of a control instruction.

– Printers, when available, should not be used as the primary means of reading the CPDLC clearance. Printed CPDLC clearances must be verified against the primary display before use.

– This information is in the GOLD manual (Doc 10037).



Administration


• Language proficiency training for pilots that use data link should include the ability to read and write Aviation English.



Administration

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