Aft Engine Mount Center Link Orientation

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February 2002 WTT face to face CFMI / Boeing Proprietary Information - Unauthorized Disclosure, Use, or Export are Prohibited 1
Aft Engine Mount Center
Link Orientation
February 2002 WTT face to face CFMI / Boeing Proprietary Information - Unauthorized Disclosure, Use, or Export are Prohibited 2
Aft Engine Mount Center Link Orientation
Event Summary
• One operator reported center link assembly, P/N 310A2034-3, found
installed reversed on one airplane
 Occurred during overhaul of aft engine mount and not noted during
aft mount installation on engine
 Center link pawl pins requiring some effort to install
 No difficulties in engine installation on airplane noted
 Further investigation revealed 5 other cases of reversed center link
on operator’s fleet
• Second operator advised Boeing of difficulty in closing thrust reversers
after No. 2 engine installation
 All mounts were found properly mating with strut
 Engine had undergone post installation engine runs with no
anomalies
 Engine was found to be rotated slightly outboard (right)
 Engine was lowered, and inspection revealed center link, P/N
310A2034-7, was reversed
February 2002 WTT face to face CFMI / Boeing Proprietary Information - Unauthorized Disclosure, Use, or Export are Prohibited 3
Aft Engine Mount Center Link Orientation
No. 1 Outboard Location
(Correct Installation)
No. 2 Outboard Location
(Incorrect Installation)
February 2002 WTT face to face CFMI / Boeing Proprietary Information - Unauthorized Disclosure, Use, or Export are Prohibited 4
Aft Engine Mount Center Link Orientation
Background
• Center link is boomerang-shaped,
attaches to hanger fitting in center and
engine lugs at either side
• Link almost symmetrical left-to-right
• Installed spherical bearings almost
identical in size
 Difference in bearing bore diameter
(1.00 inch versus 1.185 inch) not
always apparent
 Smaller left bearing and pin are
primary load path
 Larger right bearing and pin are fail
safe load path. Not normally loaded
due to clearance fit
Result:
 Link can be installed reversed in aft
mount using existing pawl pins
 Shifts aft end of engine 0.174-inch
to right
February 2002 WTT face to face CFMI / Boeing Proprietary Information - Unauthorized Disclosure, Use, or Export are Prohibited 5
Aft Engine Mount Center Link Orientation
Background (cont)
• Condition applies to the following aft engine mounts:
 P/N 310A2034-3 Center Link installed on P/N 310A2030-6 Aft Engine Mount
 P/N 310A2034-7 Center Link installed on P/N 310A2030-11 Aft Engine Mount (SAC)
 P/N 310A2034-8 Center Link installed on P/N 310A2030-12 Aft Engine Mount (DAC)
 Could be installed on any 737NG-series airplane
Status
• Reversed center link results in out-of-compliance configuration
• If condition is suspected, visual inspection can be used to check orientation
 If condition is confirmed, corrective action must be performed prior to further flight
• The following documents were revised to further clarify existing installation:
 AMM 71-21-03/401 12 February 2002 Revision
 PPBU Figure 3-1 5 February 2002 Revision
 CMM 71-21-37 1 March 2002 Revision
• More information found in following:
 FLEET TEAM Digest Article 737ng-FTD-71-01003, dated 20 Dec 2001
 Boeing Service Letter to be released shortly (late Jan/early Feb)
February 2002 WTT face to face CFMI / Boeing Proprietary Information - Unauthorized Disclosure, Use, or Export are Prohibited 6
Aft Engine Mount Center Link Orientation
Recommendations
• Ensure that the center link is installed correctly in aft mount after
overhaul
• During aft mount installation on engine, ensure no preload is required to
install either of four pawl pins securing center link and side links to
engine lugs
• Make sure no excessive force is necessary to close the thrust reversers

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Aft Engine Mount Center Link Orientation