CFM56-7B VBV Teflon Pad Disbond

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February 2002 WTT face to face CFMI / Boeing Proprietary Information - Unauthorized Disclosure, Use, or Export are Prohibited 1
CFM56-7B VBV Teflon Pad
Disbond
CFMI / Boeing Proprietary Information - Unauthorized Disclosure, Use, February 2002 WTT face to face or Export are Prohibited
Background
• About 20 cases of teflon pad disbonding reported to date
 Either seen on wing or at shop level
– 1 to 4 pads disbonded or missing
 50% cases leading to VBV position signal disagree fault occurrence
– 150 hours time limited dispatch (short time dispatch fault)
CFM56-7B VBV Teflon Pad Disbond
Pad debonded
CFMI / Boeing Proprietary Information - Unauthorized Disclosure, Use, February 2002 WTT face to face or Export are Prohibited
Root Cause Investigation
• Lack of teflon pad bonding evidence on all parts returned from field
• No manufacturing concession recorded
• All defective parts coming from same sub-contractor source
• About 1,700 pads potentially affected manufactured since EIS
 440 engines potentially affected (87X 101 - 87X 541)
Corrective Action
• Original source canceled
• New vendor process quality confirmed through shear test
– New part = 34 Mpa
– After wet aging (1500 hrs) = 22 Mpa
– CFM spec. requirement = 18 Mpa
Root Cause understood = Poor bonding quality from original vendor
CFM56-7B VBV Teflon Pad Disbond
February 2002 WTT face to face CFMI / Boeing Proprietary Information - Unauthorized Disclosure, Use, or Export are Prohibited 4
Over-serviceability
• Four pads mounted in pair, one @ 2 O’clock, one @ 8 O’clock
• If at least one pad remain at each pair location
-> serviceable, no time limit
• If one pair missing or more
-> serviceable up to shop visit
 To be introduced in the next AMM revision (Feb 2002)
EEC Software logic
• VBV position signal disagree fault maintenance message de-sensitized
 VBV fault threshold increased from fixed 4° to variable limit (function of
VBV command)
– Validated through engine test
 introduced in coming 7BN EEC software to be released in Apr 2002
CFM56-7B VBV Teflon Pad Disbond
February 2002 WTT face to face CFMI / Boeing Proprietary Information - Unauthorized Disclosure, Use, or Export are Prohibited 5
LH pair of
two pads
RH pair of
two pads
Aft looking Fwd
CFM56-7B VBV Teflon Pad Disbond
CFMI / Boeing Proprietary Information - Unauthorized Disclosure, Use, February 2002 WTT face to face or Export are Prohibited
In-service Plan
• No on-wing inspection needed
 Except for VBV fault troubleshooting per FIM
• Inspection in shop of affected population recommended
No action required if no pad disbonded
 4 pads replaced / repaired if at least one found disbonded
– Teflon pad removal requires fan minor module removal
VBV Pad Repair
• Repair bonding process has been developed and validated
 This repair does not require an industrial validation
• First repair source (Le Piston Français) to be validated by Mar 2002
CFM56-7B VBV Teflon Pad Disbond

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CFM56-7B VBV Teflon Pad Disbond