An aerodynamic stall at 41,000ft (12,470m) was followed by the almost simultaneous shutdown of both engines on the Pinnacle Airlines Bombardier CRJ200 that crashed on 14 October in Jefferson City, Missouri, says the US National Transportation Safety Board (NTSB), writes Graham Warwick.
Examination of the two General Electric CF34-3B1s found that the cores of both were free to rotate and "there was no evidence of any pre-existing problems", says the NTSB.
Pinnacle, which operates as Northwest Airlink, restricted the maximum operating altitude of its CRJs to 37,000ft after the crash of repositioning flight 3701, which killed the two crewmembers on board.
Flight data recorder (FDR) information indicates that, at 41,000ft - the certificated service ceiling for the CRJ - the stick shaker and stick pusher activated several times before the aircraft stalled and the engines shut down, the NTSB says.
After a dual flame-out, the engines can be relit using a windmill restart, which requires an indicated airspeed of at least 300kt (555km/h) and 9-12% core RPM, but the NTSB says FDR data show the computed airspeed did not get above 300kt and there was no measured rotation of the engine cores.
Alternatively, the engines can be restarted using auxiliary power unit (APU) bleed air, which must be accomplished at 13,000ft or below. The crew requested an altitude of 13,000ft after declaring an emergency at 41,000ft, and FDR data indicate the APU was on after the aerodynamic stall and the airspeed was sufficient for an APU start. But according to FDR and cockpit voice recorder data, the NTSB says, "the flightcrew tried to start the engines several times, but were unsuccessful".