NTSB Identification: LAX97IA180.
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Incident occurred Tuesday, May 13, 1997 in SAN LUIS OBISPO, CA
Probable Cause Approval Date: 01/28/2000
Aircraft: Saab-Scania AB (Saab) 340B, registration: N313AE
Injuries: 21 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 flight crew reported that all pretakeoff checks were normal and that prior to setting takeoff power the Constant Thrust on Takeoff (CTOT) computer was set to 100-percent engine torque for takeoff. The ensuing takeoff was normal through liftoff and gear retraction; however, during initial climb the left engine experienced compressor stalling and lost power. As the crewmembers were executing the engine failure checklist, the right engine first increased power in Automatic Power Reserve (APR) and then began to similarly stall and lose power. After about 20 seconds the engines recovered sufficient power to enable the flight crew to remain airborne and return for landing on the departure runway. Review of the digital flight data recorder (DFDR) output and internal examination of each engine revealed that the engines had compressor stalled due to accumulated dirt and contaminants on the compressors. A review of the right engine DFDR data revealed that, while the left engine was stalling, the flight crew had retarded the right engine power lever past the 64-degree power lever angle position which tripped off the CTOT system. The resulting transient in fuel flow, in company with an atmospheric temperature inversion, reduced the stall margin of the right engine.

The National Transportation Safety Board determines the probable cause(s) of this incident to be:

Compressor stalls of both engines due to in-service compressor contamination. Factors in the compressor stall of the right engine were an atmospheric temperature inversion and a transient fuel flow condition produced when the constant thrust on takeoff (CTOT) system was disabled by the pilot's inadvertent movement of the right engine power lever during execution of the emergency procedure.

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