NTSB Identification: CHI96IA200.
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Incident occurred Friday, June 14, 1996 in CHICAGO, IL
Probable Cause Approval Date: 09/07/2000
Aircraft: Boeing 727-30C, registration: N906UP
Injuries: 3 Uninjured.
NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.
The airplane experienced a total loss of power on all three engines, and a subsequent loss of electrical generating power, during an en route descent in preparation for landing at Greater Rockford Airport, Rockford, Illinois. The crew declared an emergency and diverted to Chicago, Illinois. A landing was made at Chicago O'Hare International Airport with all engines operating and electrical generating power restored. The investigation revealed that the airplane was modified by Supplemental Type Certificate (STC) to replace the original Pratt and Whitney engines with Rolls Royce Model TAY engines, but using the original fuel system. The original system was subject to fuel surges which were acceptable to the original installation. With the TAY engine configuration, when the airplane's fuel system is configured with one engine operating in suction feed, air and vapor evolve from the fuel in the engine and airplane fuel systems, and accumulates at the fuel system high points. When boosted fuel is restored to the system, the boosted fuel flow rate moves toward the high end of the boost pump output capacity, causing a rapid filling and recompression of the air and vapor areas with a resulting high flow velocity. The fuel is then decelerated to 'engine demand flow rate' as it reaches the engine high-pressure fuel pump. This change in the velocity of the fuel flow causes a 'pressure spike' which is first observed at the inlet to the engine high-pressure fuel pump. The formation of the pressure spike is accompanied by a rapid drop in engine high-pressure fuel pump output and fuel burner line pressures leading to a collapse in engine combustor discharge pressure and engine flameout. The formed pressure spike travels from the first engine back through the airplane's fuel system into the other exposed engines causing these engines to flameout in a similar manner. The elapsed time at which the pressure spike travels back through the fuel system to the other engines is just under one second.
The National Transportation Safety Board determines the probable cause(s) of this incident to be: low pressure in the fuel lines caused when the crossfeed valve was closed and the boost pumps to the effected fuel tank were turned off, a fuel pressure surge (spike) accompanied by a rapid drop in high pressure pump output and burner line pressures, when boosted fuel was reintroduced to the system, which resulted in temporary fuel starvation to the three engines, and the inadequate aircraft/equipment design by production personnel (STC holder). A factor which contributed to this incident was the flight engineer's management of the fuel system. Full narrative available
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