Service difficulty report · Gcu · Boeing 757224

Difficulty date
July 31, 2025
Submitted
August 4, 2025
Operation
Air carrier
Aircraft
N12109
Make and model
Boeing 757224
Aircraft serial
27299
Aircraft time
114,120 hours, 26,562 cycles
Part
Gcu
Part number
734284F
Part serial
4929
Condition
Faulty
Location
Nr 1
Part time
102,091 hours, 23,719 cycles
Stage of operation
NR
How discovered
O
Nature of condition
B, J
Precautionary procedure
A

As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.

What was found

ON ROTATION CAP FLT INSTRUMENTS BLANKED OUT. LT GEN CONTACTOR LIGHT ON RESET OK LOCKED CAPTAIN NOTIFIED THAT INSTRUMENTS CAME BACK ON WHEN LT GEN WAS RESET INSTRUMENTS OPS NORMAL REST OF FLT. APPEARS PIREP IS REFERRING TO LT GEN CONT OFF LIGHT BEING ILLUMINATED. PIREPS ON L/PS 5744410, 5742872, AND 57423866 ALL ASSOCIATED FAILURES WITH LOSS OF L 115VAC BUS. PERF 'D BPCU BITE, FLT LEG 0 HAS SINGLE FAULT FOR LT GEN PWR SYS OF "GCB/WIRING GCU". REF FIM 24-20 TASK 802 PARA U, L GCB C901 & L GCU M144 RECENTLY REPLACED. DUE TO REPORT OF ELEC SMELL, PERFORMED CONTINUITY CHKS PER WDM 24-22-11-1 PG1 FROM LEFT GEN CB C901 D1728 PINS 41 & 39 TO LT GCU M144 PINS B1,C1 OF D2108A & MEGGED WIRES NO SHORTS TO GROUND OR PIN TO PIN ALL PINS BEHIND LEFT GCU LOOK OK NO DEFECTS NOTED. ALSO CHECKED PIN 40 OF D1728 GOOD GROUND FOUND. R & R LT GEN CB C901 PER AMM 24-22-03-424-006 REQUIRES OPS CHECK PER STEP C.(4). SWAPPED LT GCU TO RT GCU POSITION.