Date: 201402
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Light: Dusk
Aircraft: A300
Operator: Air Carrier
Operating under: Part 121
Mission: Cargo / Freight / Delivery
Flight phase: Parked
Aircraft component: Circuit Breaker / Fuse / Thermocouple
Reporter organization: Air Carrier
Reporter function: Technician
Reporter qualification: Maintenance Airframe; Maintenance Powerplant
Human factors: Time Pressure; Communication Breakdown; Confusion; Situational Awareness
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Aircraft Aircraft Damaged; General Maintenance Action
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

Narrative: Weekday night; our thru-flight arrived about XA:00 PM. The pilot had a write-up; Left Inner Tank # 1 fault; no reset. When we were investigating; we found the Circuit Breaker (C/B) for the Left Inner Tank # 1 popped. Trying to make time constraints and get the flight out on time; we reset the C/B and it popped again. We wanted to isolate the problem and disconnected the Canon plug from the Left # 1 Tank Inner Fuel Pump. Reset the C/B and it stayed in. When the left # 1 Inner Tank Fuel Pump switch was turned 'On'; the C/B popped. We then decided not to reset it and find out what was causing it to pop. I was not as familiar with the General Maintenance Manual (GMM) 6-1-250 [Dimensions/Areas] pertaining to this matter as I thought. I have reviewed it carefully and thoroughly to prevent this from happening again. We were trying to solve this write-up in a timely and safely matter and were not trying to do anything wrong on purpose. The aircraft was not dispatched and was not going to be until the problem was fixed. We used our weekend layover aircraft to move the freight. Once again GMM 6-1-250 will be thoroughly reviewed and I will keep a copy of it close at hand. [Problem] possibly with older aircraft; wire fatigue and over time; wire broke down and caused Circuit Breaker to pop. Also Avionic's technicians thought [wire] bundle was tied too tight with [electrical] wires rubbing together. We; Aircraft Line Mechanics' have to keep up with many; many; many Maintenance Alerts. Could we possibly take a recurrency test on the Maintenance Alerts that are considered extremely important; although keep in mind they are all important. Also maybe make up a quick Maintenance Alert booklet; like the Mechanic's Quick Trouble Shooting (T/S) Guide; containing the very critical alerts. Rain. Aircraft damage.

Callback: Reporter stated he has thirty-five years aircraft maintenance experience. The evening was cold and wet on the Line.  An inbound flight crew had reported the left #1 fuel tank inner fuel boost pump circuit breaker (C/B) had popped. The flight crew did not try to reset the C/B.  However; he and an Avionics Technician had reset the boost pump C/B twice during troubleshooting.  That had deviated from their General Maintenance Manual (GMM) Chapter Six procedures which allowed only one reset of the affected C/B unless more in-depth fuel system testing was accomplished. Unknowingly; they had not performed those additional steps; they were just trying to isolate the C/B problem. He now keeps a copy of the GMM Chapter-6 reference next to his work desk. Reporter stated the circuit breaker for the boost pump is down in the avionics bay (E/E compartment) which can be accessed through a cockpit floor hatch; or through the lower forward cargo compartment interior door at the forward bulkhead. His Avionics Technician partner noted that the boost pump C/B and the wire harness to that C/B was OK and in a well protected area above the three aircraft batteries that are located on the right side of the avionics bay.  But approximately nine inches from that C/B the same electrical harness had burned wires that appeared to have been caused by excessively tight tie-wraps installed by the aircraft manufacturer.  A forward cabin galley section would normally be above that area. Suspicions are that inflight vibrations caused some of the individual wire insulations to chafe against the tie-wraps that held the wire bundle. This was the second time he has seen a similar burned wiring condition in the same area. On a previous A300 aircraft; environmental splices had been installed where the wire harness run should not have had any breaks in the wire bundle.  The recent A300 aircraft had been taken out of service and never left the station until repaired.  Most; if not all; of their A300s were purchased from other operators. He wonders if these two incidences would fall under the 'Aging Aircraft' description.



Synopsis: A Line Aircraft Maintenance Technician (AMT) reports a circuit breaker (C/B) for the left #1 fuel tank; inner fuel boost pump continued to pop; even with the cannon plug to the fuel pump disconnected on an A300 aircraft. Burned wires in a wire harness to the boost pump C/B were found at a tie-wrap installation in the avionics compartment.