Crew’s decision to explore edges of aircraft’s flight envelope led to disaster

The hitherto mysterious double engine failure on a Pinnacle Airlines Bombardier CRJ200 has been revealed as a flame-out caused by a combination of high altitude and intake turbulence resulting from high angle of attack and wing stall.

According to a US National Transportation Safety Board (NTSB) initial factual report on the 14 October 2004 fatal accident, the aircraft arrived at the pilots’ requested altitude of 41,000ft (12,500m) behind the drag curve at Mach 0.57, with indicated airspeed reducing.

Flight level 330 was the height identified as best for fuel burn on the Little Rock-Minneapolis/St Paul positioning flight, but a verbal exchange with the controller revealed the pilots decided to try flying at the aircraft’s service ceiling for “a little fun” (Flight International, 8-14 March).

The NTSB says there is no evidence as to whether or not the crew consulted the aircraft operating manuals, but it has since been estimated that the maximum altitude for the weight and conditions was 40,000ft.

When they reached their planned level the pilots quickly realised the aircraft’s airspeed was falling and they asked for a lower level. The aircraft stalled fully, with the stick-pusher operating four times in 20s, and the engines flamed out. During this period the maximum recorded angle of attack was 27º. Finally the nose pitched down 32º, with 82º left wing low. Cockpit voice recorder (CVR) playback indicates the crew realised they had a double engine failure. They reported an emergency and the need for descent, but did not report for 17min that they had a double engine failure and needed vectors to the closest airport.

Meanwhile, they tried several times to relight the engines, but with no success. The continuing NTSB investigation is examining whether the engines suffered core lock, a phenomenon caused by differential cooling of static engine parts compared with the internal rotating core. The NTSB found the turbines had suffered overtemperature, which can exacerbate core lock. Absence of engine windmilling was recorded during much of the descent.

The aircraft crashed 2.5nm (4.6km) south of Jefferson City airport, Missouri, to which it was being vectored by air traffic control. Half of the left wing was torn off by the first impact with a tree. The aircraft rolled left and hit more trees before coming to a halt inverted. Both pilots died in the accident.

Flight descent progress
The cockpit voice recorder was active throughout. The flight data recorder (FDR) was briefly interrupted after the double engine failure, but restored when the auxiliary power unit (APU) was started. Timeline is local time.

21:52:08 crew notifies ATC on reaching FL 410 (41,000ft/12,500m);
21:54:31 crew reports unable to maintain level, requests lower;
21:54:38 stick-shaker activated, followed by stickpusher operating four times in next 20s;
21:54:58 FDR confirms attitude 32º nose down and 82º left wing low;
21:55:05 engines fail and crew declares emergency;
21:55:21 FDR stops;
21:59:17 FDR starts with the APU power;
21:59:51 crew requests descent to 13,000ft;
22:03:14 ATC asks what the emergency is. Captain gives confusing reply. Controller believes only one engine has failed;
22:09:06 crew tells ATC for first time that they have a double engine failure and requests vectors for nearest airfield. Controller provides vectors to runway 30 at Jefferson City airport;
22:09:15 crew reports descent rate 1,500ft/min (8m/s), passing 9,500ft;
22:13:19 crew reports on vector heading 360º, says airport is not in sight;
22:14:39 first officer says aircraft is not going to make it to the runway;
22:15:07 aircraft hits ground 2.5nm (4.6km) south of airport.

DAVID LEARMOUNT/LONDON

Source: Flight International

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