Aviation Investigation Report A98H0003

1.12.8  Examination of Fuel System Components

All 17 of the 115 V AC motor-driven fuel pumps were recovered, and all but two were specifically identified as to their installed location. Each fuel pump receives electrical power from one of the three AC generator buses, and each pump in each of the fuel tanks is powered from a different electrical power source. All of the pumps were examined at the fuel pump manufacturer's facility to determine whether they were being electrically driven at the time of impact, which would provide information about the status of the electrical buses.

The fuel pump examination focused on identifying distinctive damage that would indicate whether the pumps were operating (turning) at the time of impact. Distinctive damage included gouge marks on the impeller housing, denoting contact between the housing and the rotating or stationary impeller blades, and damage to the pin-and-slot arrangement that holds the impeller to the rotating shaft. The damage showed that six pumps had high rotational energy at the time of impact, indicating that their impellers were being electrically driven.

Fuel Tank 2 left aft boost pump housing displayed distinct imprints that were caused by the impeller while it was stationary; it was determined that this impeller was not being electrically driven at the time of impact.

A determination of the operational status of the remaining pumps could not be made, as there was lack of physical damage, and therefore no definitive marks. Table 14 identifies the six fuel pumps that were determined to have been operating at the time of impact and the source of electrical power associated with each.

Table 14: Fuel Pumps Determined to Be Operating at Impact

Fuel Pump Location Electrical Bus
Tank 1 Forward Boost Pump 115 V AC Generator Bus 1
Tank 3 Transfer Pump 115 V AC Generator Bus 1
Upper Auxiliary Right Transfer Pump 115 V AC Generator Bus 1
Tail Tank Left Transfer Pump 115 V AC Generator Bus 1
Tank 1 Aft Boost Pump 115 V AC Generator Bus 3
Tank 2 Transfer Pump 115 V AC Generator Bus 3

Both fuel dump valves were recovered and examined. The observed damage and gouge marks indicate that both valves were in the CLOSED position at the time of impact.

The auxiliary tank fill/isolation valve, and the tail tank fill/isolation valve, were recovered and examined. Impact forces captured the valve slides in both valves in the CLOSED position at the time of impact. In accordance with the known fuel system configuration and normal FSC operation, the tail tank fill/isolation valve would be expected to be closed. However, the auxiliary tank fill/isolation valve should have been open at the time of impact, unless either electrical power was not available to open it or fuel dumping had been initiated at some point. That is, during fuel dumping, the fuel system is reconfigured to close the auxiliary tank fill/isolation valve.

Only portions of the three cross-feed valves were recovered; the position of their valve slides at the time of impact could not be determined.

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Date modified :
2012-07-27