pratt & whitney jt8d engine maintenance planning guide

JT8D-STD SERIES ENGINE MAINTENANCE PLANNING GUIDE

PN 820671

Orig. Date: 11/15/99 Rev. Date: 11/06/09 File Name: JT8D_STD_IV_14_MGBX

PART IV: WORKSCOPE PLANNING GUIDE SECTION 14: MAIN GEARBOX (MGBX)

Reference 14.1 BUILD GROUP GENERAL EM 72-61-00 14.1.1 GENERAL

a) Review JT8D-STD #1 Reliability Service Bulletins applicable to the Build Group.

b) Determine level of maintenance using factors including but not limited to:

•

•

•

•

•

TSLSV / CSLSV & TSLHM / CSLHM

Engine removal schedule

c) Maintenance levels for this module are:

Module Level Inspection

For modules that are not scheduled for disassembly that are either installed or removed from the engine.

Check & Repair / Modification

For modules that are partially disassembled to allow access to specific parts requiring repair or modification only without performing any performance or stability related refurbishments.

Heavy Maintenance

For modules that are beyond the recommended threshold for heavy maintenance or require complete disassembly and refurbishment to restore performance and stability. This workscope sets the TSLHM / CSLHM to zero as major rotating parts are fully disassembled and NDT inspected.

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Reference 14.1 BUILD GROUP GENERAL EM 72-61-00

14.1.2 DETERMINATION OF LEVEL OF MAINTENANCE

The decision tree chart that follows provides guidance for determining the level of maintenance for this group.

GEARBOX In-Shop

Module Level Inspection results

unacceptable?

No further action required.

Check & Repair / Modification

NO

YES

YES

Heavy Maintenance

TSLHM /CSLHM or TSN /CSN exceeded

H/M interval recommendation (1)

or scheduled H/M (2) or Removed for

maintenance history

NO

Significant oil leakage noted? Or

Accumulation of chips on chip detectors or

operational problems

NO Gearbox removed for extensive damage due to

an engine event?

YES

NO

YES

Note (1): Refer to WPG Section 2, General Information, Table 2.3.4, “Gearbox Heavy Maintenance Soft Time Interval” (2): Gearboxes that have accumulated high time/cycle, but have not exceeded H/M interval. Also consider

factors such as: LLP, hardware condition, etc.

Note: Depending on the level of maintenance workscope being performed and parts exposure, Pratt & Whitney recommends incorporation of Service Bulletins in reference to # 1 Reliability, Categories 1 through 6, and the Minimum Build Standard. Pratt & Whitney also recommends incorporation of Categories 7 and 8 Service Bulletins that are applicable to each gearbox based on the operator’s service and maintenance experience.

However, regardless of the level of maintenance workscope being performed, operators should comply with FAA mandated AD Notes and Pratt & Whitney issued Alert Service Bulletins pertaining to the gearbox.

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14.1.3 FOCUS AREAS

a) Bearing deterioration.

b) Carbon seal deterioration.

c) CSD gearshaft disengagement.

d) Main oil pump assembly.

e) Housing split line oil leakage.

f) Mail oil filter cover leaks.

g) JT8D-ALL ACCESSORY BEARING MAINTENANCE RECOMMENDATIONS:

A JT8D SIR Article provided maintenance recommendations for accessory bearings based on a field survey of customers and shops and successful implementation in the field. It discusses the following topics: June 2003 JT8D

Service Information Report (SIR) Article (pages 10, 11 & 12) – Maintenance Practices Guidelines To Preclude Premature JT8D Oil Pump Drive Gear Bearing Failures

• Bearing light maintenance inspection criteria • Bearing heavy maintenance inspection criteria • Re-use of old bearings vs. the installation of new bearings • Proper disassembly, inspection, repair, and re-assembly

procedures to extend the service life of the MGB • MOF selection & • Engine oil monitoring

The intent was to provide a realistic, field experience based, comprehensive recommendation platform, as a basis, for our customers. It also states that

individual customer analysis, with regard to the re-use

or the replacement of accessory bearings, is necessary to determine if this same philosophy would be beneficial. P&W provides

accessory bearing inspection criteria and allows for “source demonstration approved” accessory bearing refurbishment.

Our current accessory bearing maintenance recommendations is similar and provided below. Please note that the only change in recommendations from the SIR article is a change in the Heavy Maintenance interval (from 10,000-14,000 hours) to 10,000-12,000 hours. This change was made to agree with the other Heavy Maintenance soft time interval given in this MPG.

1) Bearing Check & Repair (Light Maintenance) Inspection Criteria:

Inspect bearings for hardness, bore diameter, outside diameter, and internal radial clearance whenever that bearing has more than 6,000 hours since new, or refurbishment, and the Main Accessory Gearbox is opened (Front Cover removed). For customers experiencing a high rate of premature failure, the bearings should be inspected whenever the Main Accessory Gearbox is available (removed from the engine), in addition to whenever the Front Cover is removed.

JT8D-Std & -200 Engine Manuals, 72-09-52, Inspection-01– Accessory Bearing Visual Dimensional Inspection

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2) Bearing Heavy Maintenance/Overhaul Inspection Criteria: Standard Practices Manual, 70-35-00, Insp/Check -01

Replace or Inspect the bearing (Level 1 and Level 2 - full serviceability inspection by a P&W approved source) at 10,000 – 12, 000 hours. See below for more information on the option to replace or inspect & repair. This interval can be used as an initial starting point and could be adjusted (up or down) depending on the customer’s experience.

– Engine Bearings – Antifriction Bearing Inspection NOTE: Standard Practices Manual, 70-35-00, Insp/Check-02

The referenced JT8D Engine Manual (72-09-52, INSP-01) provides serviceability inspection requirements for Accessory Bearings. Within this procedure is a NOTE that directs these procedures to all “demountable” or “semi-demountable” JT8D accessory bearings. These “demountable” or “semi-demountable” types of bearings are defined as those on which it is possible to remove an inner or outer race (without using tools) and do an inspection of the balls or rollers.

– Visual Inspection – Antifriction Bearing Inspection JT8D-Std & -200 Engine Manuals, These bearings should be inspected as described in the Standard

Practices Manual (Section 70-35). The Engine Manual provides hardness, bore diameter, outside diameter, and internal radial clearance requirements. These requirements should be thought of as tables of “fits & clearances” and, in the case of Heavy Maintenance, do

72-09-52, Inspection-01 – Accessory Bearing Visual Dimensional Inspection

not comprise the complete serviceability inspection. The Engine Manual also states that defects on the “functional surfaces” of a bearing are the most important to find. These “functional surfaces” of a bearing are the ball or roller surfaces, all parts of an inner or outer race that touch the balls or rollers, and the parts of the bearing cage that touch the balls or rollers.

JT8D-Std & -200 Engine Manuals, 72-09-52, Repair-00 – Accessory Bearing Repair/Part No. Index

To do the functional surfaces inspection, bearings must be disassembled by removing the retention-rivets and separating the two cage halves. This disassembly (and subsequent cleaning, inspection, refurbishment, and reassembly) must be done by a P&W approved source as indicated in the Engine Manual (72-09-52, REPAIR-00 & REPAIR-01). Only Level 1 (cleaning, visual inspections, and dimensional inspections) and Level 2 (Level 1 plus replacement of roller elements, re-plating/replacement of the retainer, raceway honing to 0.0003” Max., no grinding is permitted) are allowed.

JT8D-Std & -200 Engine Manuals, 72-09-52, Repair-01 – Recondition Accessory Drive Gearbox Bearings Repair (Vendor Application)

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3) Installation of new bearings vs. used/refurbished bearings:

Some customers that experienced premature bearing failures have adopted a maintenance philosophy of installing “new” bearings at heavy maintenance (overhaul) and have seen a significant improvement in service life, compared to refurbished bearings. In one case, the customer has stated that new bearings installed at overhaul provide failure free service to the next scheduled Main Accessory Gearbox overhaul (16,000 hours or more) and that they are currently getting as much 26,000 – 29,000 hours between overhauls. In some cases, they have accumulated as much as 30,000 hours without problems.

Individual customer analysis is necessary to determine if this same philosophy would be beneficial. This analysis must consider both the technical merits (ability to achieve the required service life without problems) and the economics of costs associated with the complete inspection of the bearing (by a P&W approved source) and follow-on refurbishment vs. the cost of a new bearing.

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Reference14.2 BUILD GROUP LEVEL INSPECTION

14.2.1 GENERAL

a) Visually inspect the Main Accessory Gearbox Group for obvious surface defects and/or deformations, which will preclude proper functioning of any of the parts.

b) The inspection limits and repairs referenced for build group level inspection are intended to be performed on the listed parts only when assembled as a complete build group and are not to be applied to disassembled parts. Individual parts that are removed as a result of providing access for inspection of the build group shall receive a minimum of visual inspection. If visual inspection reveals unserviceable conditions, parts shall be fully inspected and repaired

c) This section covers all parts that may be exposed for inspection on an assembled gearbox. It is recognized that not all of these parts may be exposed depending on the level of engine disassembly. It is not necessary to perform additional disassembly for the sole purpose of exposing the listed parts. However, if inspection reveals a questionable condition that cannot be confirmed in assembled state, further disassembly shall be accomplished to ensure the condition does not affect the airworthiness of the engine.

14.2.2 INSTALLED ON ENGINE OR REMOVED EM 72-00-00 Check-01

a) Visually inspect: •

•

Accessory mounting pads and ports for evidence of oil leakage. Gearbox front to rear housing split line for evidence of oil leakage.

MM 72-00-00 Insp/Check-01

Note: It is recommended that oil strainer or filter be removed for inspection at 250 - 400 hour intervals.

b) Remove and inspect the two magnetic chip detectors (if used).

c) Visually inspect exposed accessory drive splines and gears for wear.

Standard Practices Manual

d) If gearbox is removed, inspect tower shaft mounting areas for condition.


e) Visually inspect exposed surfaces of the gearbox for general conditions.

EM 72-61-00 Check-01

f) Inspect CSD drive gear movement. Remove CSD if necessary.

EM 72-61-01 Inspection-01

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Reference14.3 CHECK & REPAIR / MODIFICATION

EM 72-00-00 14.3.1 DISASSEMBLY

a) Disassemble the gearbox as necessary to perform specific repairs or modifications.

EM 72-61-00 Disassembly-01

14.3.2 GENERAL

a) Cleaning of parts is not required. b) Visual Inspect exposed areas (not disassembled) for

damage and distress that will preclude proper functioning of any of the parts. For conditions not described below refer to the EM individual part Visual Inspect section for damage limits. Parts that pass visual inspection requirements may be returned to service. Parts that fail shall receive full inspection and repair in accordance with EM requirements.

c) For exposed parts treat all fits as IFR code B unless otherwise specified.

14.3.3 GEARBOX ASSEMBLED OR PARTIALLY DISASSEMBLED

a) Inspect gearbox main mount for pin-to-hanger and pin-to-gearbox wear and front mount for bolt-to-gearbox wear.


b) Check for damaged, pulled, or loose studs. c) Visually inspect all accessible areas of the gearbox for

general conditions. EM 72-61-00 Check-01

d) Inspect CSD drive gear movement. Remove CSD if necessary.

e) Disassemble, Clean, and Visual Inspect oil pressure relief valve.


f) Visual Inspect all bearing journals and bearings, if removed.


Note: Reference Focus Points, Item g for Bearing Maintenance Recommendations.

g) If fuel pump is removed, inspect gearbox mount pad and QAD ring. If installed, tap and torque QAD ring.

EM 72-61-61 EM 72-61-62 EM 72-61-63

h) In-situ visual inspection of hydraulic pump gearshaft, rear internal spline.


i) Replace all oil pump seals. j) Inspect all exposed gears and splines for wear. Repair

if necessary.

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Reference14.4 HEAVY MAINTENANCE

EM 72-00-0014.4.1 DISASSEMBLY a) Remove Main Accessory Gearbox (MGBX) group. EM 72-00-61

Removal-01 or Removal-02

b) Remove external components from main accessory gearbox assembly.

EM 72-00-61 Removal-03 Removal-04 Removal-05 Removal-06 Removal-07 Removal-08 Removal-09 Removal-10 Removal-11 Removal-12 Removal-13 Removal-14 Removal-15 Removal-16 Removal-17 Removal-18 Removal-19 Removal-20 Removal-21 Removal-22 Removal-23 Removal-24 Removal-25 Removal-26 Removal-27

c) Disassemble gearbox assembly to individual parts and subassemblies.

EM 72-61-00 Disassembly-01

14.4.2 GENERAL

a) Cleaning of parts is required. EM 72-61-00 Cleaning-01

b) The workscope instructions provided in this section represent P&W recommendations that encompass a broad range of conditions an engine may be subjected to. Individual operators / heavy maintenance shops may use knowledge gained through their operating experience to modify this workscope.

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EM 72-00-00 Inspection-01 &

c) Dimensional Inspection of part features are required for IFR code A fits, clearances, and limits only unless otherwise specified. Dimensional Inspection of IFR code B fits are required only if assembly criteria are not met unless otherwise specified. (See EM definition of IFR code B)


d) Individual parts not covered in the EM shall receive a minimum of visual inspection.

EM 72-09-00

e) Refer to Section 19, Recommended Oil Systems Best Build Practices for additional recommendations pertaining to the gearbox Build Group.

EM 72-00-00 Special Procedure-01

EM 72-61-01 14.4.3 HOUSING ASSEMBLY, GEARBOX REAR

a) Remove strainer element assembly. Disassembly-01

b) Remove gearbox flange clamp body. (Post S/B 6097) Disassembly-03

c) FPI EM 72-61-00 Inspection-01

d) Visual Inspect for general physical condition. EM 72-61-01 Inspection-01

e) Dimensional Inspect mount lug bushings for wear. Inspection-02

f) Install strainer elements into gearbox housing. Assembly-01

g) Oil Nozzle - installation for Flow Test. Assembly-03

h) Oil Flow Test assembly. Assembly-04

i) Install gearbox flange clamp body. (Post S/B 6097) Assembly-05 EM 72-61-02 14.4.4 HOUSING ASSEMBLY, GEARBOX FRONT

a) FPI EM 72-61-00 Inspection-01

b) Visual Inspect for general physical condition. EM 72-61-02 Inspection-01

c) Dimensional Inspect bearing to bushing fits. Inspection-02 EM 72-61-10 14.4.5 STARTER DRIVE GEARSHAFT ASSEMBLY a) Visual Inspect for general physical condition. Inspection-01

14.4.6 STARTER DRIVE SPUR GEARSHAFT (ASSEMBLY) EM 72-61-11

a) Visual and Dimensional Inspect. Inspection-01

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14.4.7 ROTARY DEAERATOR IMPELLERS (FRONT AND REAR)

EM 72-61-12


14.4.8 STARTER DRIVE GEARSHAFT COUPLING EM 72-61-14


14.4.9 GEARBOX DRIVE BEVEL AND SPUR GEARSHAFT ASSEMBLY

EM 72-61-15 EM 72-61-16

a) FMPI

b) Visual and Dimensional Inspect.

Inspection-01

14.4.10 ACCESSORY AND COMPONENT DRIVE GEARSHAFT

ASSEMBLY EM 72-61-20 EM 72-61-21

a) FMPI


Inspection-01

14.4.11 ACCESSORY DRIVE BEVEL GEAR (CSD) EM 72-61-22

a) FMPI Inspection-01


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14.4.12 GEARBOX COUPLING (CSD) EM 72-61-23

a) FMPI


Inspection-01

14.4.13 FUEL PUMP DRIVE GEARSHAFT ASSEMBLY EM 72-61-25 EM 72-61-26

a) FMPI


Inspection-01

14.4.14 GEARBOX DRIVE SPUR GEAR EM 72-61-27

a) FMPI


Inspection-01

14.4.15 HYDRAULIC PUMP DRIVE GEARSHAFT ASSEMBLY EM 72-61-30 EM 72-61-31

a) FMPI


Inspection-01

14.4.16 GEARBOX DRIVESHAFT (OUTER) COUPLING EM 72-61-36


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14.4.17 GEARBOX DRIVESHAFT BEVEL GEAR EM 72-61-37

a) FMPI


Inspection-01

14.4.18 TACHOMETER DRIVE (N2) GEARSHAFT ASSEMBLY EM 72-61-40 EM 72-61-41

a) FMPI


Inspection-01

14.4.19 TACHOMETER DRIVE OIL SEAL HOUSING AND SEAL EM 72-61-44

a) Disassemble tachometer drive oil seal housing and seal.

b) Assemble tachometer drive oil seal housing and seal.

Disassembly-01

Assembly-01

EM 72-61-50 14.4.20 MAIN OIL PUMP

a) Visual inspect bearing, gears, housings, seals etc.

b) Dimensional Inspect.

Inspection-01

Inspection-02

EM 72-61-51 14.4.21 OIL PRESSURE RELIEF VALVE ASSEMBLY

a) Visual Inspect strainer, housing, detail parts.


Inspection-01

Inspection-02

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EM 72-61-54 14.4.22 MAIN OIL FILTER (15 MICRON)

a) Clean or replace (operator option).

b) Oil Pressure Check pressure relief valve.

Inspection-01

EM72-61-55 14.4.23 MAIN OIL STRAINER OPTION (40 MICRON)

a) Clean the strainer and its parts.

b) Backflush the strainer with clean water.

Cleaning-01

c) Measure spring compression. Inspection-01

d) Visual Inspect: Inspection-02

• Reusable type strainer elements.

• The oil strainer cover for damage and warping.

EM 72-61-58 14.4.24 POWER LEVER CROSS SHAFTS

a) Visual Inspect:

• Bearing journals.

• Fluorocarbon bearings for wear.

• Internal / external spline wear, etc.

Inspection-01

b) Dimensional Inspect bearing and spline wear. Inspection-02

EM 72-61-59 14.4.25 ACCESSORY DRIVE FACE TYPE OIL SEALS

a) Visual Inspect for nicks, cracks, dimensions etc. Inspection-01

b) Replace deoiler carbon seal with new; re-lap starter drive gearshaft seal face.

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EM 72-09-52 14.4.26 ACCESSORY BEARINGS a) Visual Inspect for general physical condition. Standard Practices

Manual b) Dimensional Inspect.

Note: Reference Focus Points, Item g for Bearing Maintenance Recommendations.

Inspection-01

c) Inspect all functional surfaces. See SIR June 2003 Maintenance Practices Guidelines

EM 72-61-60 14.4.27 FUEL CONTROL LINKAGE

a) Visual Inspect:

• Links and link bearings for wear or damage.

Inspection-01

b) Apply antigalling compound to threads. Repair-01

EM 72-61-61 EM 72-61-62

14.4.28 FUEL PUMP COUPLING (QUICK DISCONNECT), FRONT AND REAR

a) Visual Inspect for wear or damage.


Inspection-01

Front Coupling

Rear Coupling

EM-72-61-63 14.4.29 GEARBOX QUICK DISCONNECT NUT

a) Dimensional Inspect threads for wear. Inspection-01

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EM 72-61-65 14.4.30 OIL TANK

a) Visual Inspect: Inspection-01

• For dents, distortion, etc.

• Oil outlet tube support bracket weld.

EM 72-61-66 14.4.31 OIL TANK CAP ASSEMBLY

a) Visual Inspect: Inspection-01

• For broken, missing, and damaged parts.

• Gage (if installed) for readability of markings.

EM 72-61-67 14.4.32 OIL TANK STRAP ASSEMBLY

a) Visual Inspect for: Inspection-01

• General physical condition.

• Cushion bonding.

EM 72-61-68 14.4.33 ACCESSORY DRIVE OIL SEAL HOUSINGS

a) Dimensional Inspect face wear. Inspection-01

EM 72-61-69 14.4.34 GEARBOX HOUSING GASKET

a) Visual Inspect for: Inspection-01

• Aluminum base for surface corrosion or damage.

• Rubber section for cuts, scores, or damage.

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EM 72-61-80 14.4.35 GEARBOX MOUNTING PINS

a) Visual Inspect for hardface wear into parent material. Inspection-01

EM 72-61-81 14.4.36 GEARBOX MOUNTING BOLTS

a) Visual Inspect for general physical condition. Inspection-01

b) Replace antigalling compound. Repair-01

EM 72-61-00 14.4.37 GEARBOX GROUP ASSEMBLY

a) Perform Leak Test of assembled gearbox. Assembly-01

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pratt & whitney jt8d engine maintenance planning guide

Documents

level of maintenance

maintenance history

maintenance experience

heavy maintenance tslhm

main gearbox mgbx reference

review jt8dstd

build group general

determination of level