Narrative:

We flew the first leg of a multi-leg trip that had our charter B-747 flying two round trip charters in 4 days. On this first day of the operation we encountered a significant maintenance issue that could have jeopardized the entire sequence. After the aircraft was loaded with 286 passengers all the doors were closed we were ready to start engines. We observed the #2 APU generator drop off line and the #2 APU field relay open. We began to troubleshoot this issue and observed several other electrical anomalies occurring. We were in the process of running the single generator start checklist when we heard the sound of multiple electrical relays clicking in the overhead panel. This was followed by the #1 APU generator dropping off line and its field relay opening. The entire airplane was now dark due to loss of all AC power and a very strong odor of electrical burning or arcing was detected by everyone on the upper deck. We established communication with operations and advised them of the situation and asked for the immediate return of the airstairs so that we could open a door; since we were without the ability to remove the growing electrical smell without normal AC power. An increasingly strong odor of electrical burning was now being reported by all cabins in the aircraft. We advised ATC of the problem and asked that they provide fire rescue assistance to us as we did not know the severity of the problem. Within minutes of the airstairs and fire department arriving; I decided to deplane all passengers since we could not clear the cabin air. We successfully deplaned all 286 passengers onto the ramp east of the airplane. For the next 3 hours the first officers worked with maintenance control; dispatch; the charter operations department; the flight attendants; local station personnel and the two local avionics and tech ops technicians to troubleshoot the problem. Due to the significant efforts of the two first officers assisting the maintenance techs; who had limited 747 background; we were finally able to isolate the problem to both of the APU generators. Due to the extensive strong odor of electrical burning we wanted to make sure that there was no visible damage to the wiring of the APU generators. First officers worked actively in assisting maintenance in this process for over two hours. After making sure that all departments were in agreement that we could safely continue the operation we deferred the inoperative systems and re-boarded the passengers. We used a single ground power unit to power the aircraft. We discussed our personal desire to complete an engine run and establish full electrical power to all systems of the aircraft prior to accepting the aircraft for a 9 hour oceanic flight since a single ground power unit would not power all systems normally. I determined that the normal engine start sequence would satisfy our concerns about the systems integrity and since maintenance control and dispatch had already released the aircraft for flight; I decided that calling the duty manager and asking for permission for an engine run would only further delay our departure on this critical first leg of the multi-day trip.during the normal engine start; we encountered a significant problem with the first engine started. The aircraft failed to accept power from the single aircraft generator to power the aircraft tie bus. With the #1 engine running we worked this new electrical issue with maintenance control and eventually were able to get all four engines started and electrically online. Once normal electrical power was established to all operational systems we were able to ensure that all systems were now operating properly and there was no recurrence of the strong electrical odor. This engine start sequence and troubleshooting with maintenance control took 20 minutes. I now understand that if we need to have the engines run to satisfy our safety concerns regarding the system integrity; that I should take the time needed to obtain maintenance control approval for the engine run and system check.

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Original NASA ASRS Text

Title: B747 flight crew experiences the sequential failure of APU generator number two then number one; followed by strong electrical fumes; while preparing for engine start. After several hours of troubleshooting both APU generators are deferred and the crew is able to start engines and depart after dealing with one additional generator anomaly on the number one engine.

Narrative: We flew the first leg of a multi-leg trip that had our charter B-747 flying two round trip charters in 4 days. On this first day of the operation we encountered a significant maintenance issue that could have jeopardized the entire sequence. After the aircraft was loaded with 286 passengers all the doors were closed we were ready to start engines. We observed the #2 APU generator drop off line and the #2 APU field relay open. We began to troubleshoot this issue and observed several other electrical anomalies occurring. We were in the process of running the single generator start checklist when we heard the sound of multiple electrical relays clicking in the overhead panel. This was followed by the #1 APU generator dropping off line and its field relay opening. The entire airplane was now dark due to loss of all AC power and a VERY strong odor of electrical burning or arcing was detected by everyone on the upper deck. We established communication with operations and advised them of the situation and asked for the immediate return of the airstairs so that we could open a door; since we were without the ability to remove the growing electrical smell without normal AC power. An increasingly strong odor of electrical burning was now being reported by all cabins in the aircraft. We advised ATC of the problem and asked that they provide fire rescue assistance to us as we did not know the severity of the problem. Within minutes of the airstairs and fire department arriving; I decided to deplane all passengers since we could not clear the cabin air. We successfully deplaned all 286 passengers onto the ramp east of the airplane. For the next 3 hours the First Officers worked with Maintenance Control; Dispatch; the charter operations department; the flight attendants; local station personnel and the two local avionics and tech ops technicians to troubleshoot the problem. Due to the significant efforts of the two first officers assisting the maintenance techs; who had limited 747 background; we were finally able to isolate the problem to both of the APU generators. Due to the extensive strong odor of electrical burning we wanted to make sure that there was no visible damage to the wiring of the APU generators. First Officers worked actively in assisting maintenance in this process for over two hours. After making sure that all departments were in agreement that we could safely continue the operation we deferred the inoperative systems and re-boarded the passengers. We used a single ground power unit to power the aircraft. We discussed our personal desire to complete an engine run and establish full electrical power to all systems of the aircraft prior to accepting the aircraft for a 9 hour oceanic flight since a single ground power unit would not power all systems normally. I determined that the normal engine start sequence would satisfy our concerns about the systems integrity and since Maintenance Control and Dispatch had already released the aircraft for flight; I decided that calling the Duty Manager and asking for permission for an engine run would only further delay our departure on this critical first leg of the multi-day trip.During the normal engine start; we encountered a significant problem with the first engine started. The aircraft failed to accept power from the single aircraft generator to power the aircraft tie bus. With the #1 engine running we worked this new electrical issue with Maintenance Control and eventually were able to get all four engines started and electrically online. Once normal electrical power was established to all operational systems we were able to ensure that all systems were now operating properly and there was no recurrence of the strong electrical odor. This engine start sequence and troubleshooting with Maintenance Control took 20 minutes. I now understand that if we need to have the engines run to satisfy our safety concerns regarding the system integrity; that I should take the time needed to obtain Maintenance Control approval for the engine run and system check.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.