TURKISH AIRLINES FLIGHT 1951

Accident description

Status:	Final
Date:	25 FEB 2009
Time:	10:26
Type:	Boeing 737-8F2
Operator:	Türk Hava Yollari - THY
Registration:	TC-JGE
C/n / msn:	29789/1065
First flight:	2002-01-24 (7 years 1 months)
Engines:	2 CFMI CFM56-7B26
Crew:	Fatalities: 4 / Occupants: 7
Passengers:	Fatalities: 5 / Occupants: 128
Total:	Fatalities: 9 / Occupants: 135
Airplane damage:	Destroyed
Airplane fate:	Written off (damaged beyond repair)
Location:	1,5 km (0.9 mls) S of Amsterdam-Schiphol International Airport (AMS) (Netherlands)
Phase:	Approach (APR)
Nature:	International Scheduled Passenger
Departure airport:	Istanbul-Atatürk International Airport (IST/LTBA), Turkey
Destination airport:	Amsterdam-Schiphol International Airport (AMS/EHAM), Netherlands
Flight number:	1951

Narrative

Turkish Airlines Flight TK1951, a Boeing 737-800, departed Istanbul-Atatürk International Airport (IST) for a flight to Amsterdam-Schiphol International Airport (AMS), The Netherlands. The flight crew consisted of three pilots: a line training captain who occupied the left seat, a first officer under line training in the right seat and an additional first officer who occupied the flight deck jump seat. The first officer under line training was the pilot flying. The en route part of the flight was uneventful.

The flight was descending for Schiphol and passed overhead Flevoland at about 8500 ft. At that time the aural landing gear warning sounded. The aircraft continued and was then directed by Air Traffic Control towards runway 18R for an ILS approach and landing. The crew performed the approach with one of the two autopilot and autothrottle engaged. The standard procedure for runway 18R prescribes that the aircraft is lined up at least 8 NM from the runway threshold at an altitude of 2000 feet. The glide path is then approached and intercepted from below. Lining up at a distance between 5 and 8 NM is allowed when permitted by ATC. Flight 1951 was vectored for a line up at approximately 6 NM at an altitude of 2000 feet. The glide slope was now approached from above.

The landing gear was selected down and flaps 15 were set. While descending through 1950 feet, the radio altimeter value suddenly changed to -8 feet. And again the aural landing gear warning sounded.

Once the localizer was intercepted the crew selected, by means of the vertical speed mode of the auto pilot, a descent speed of 1400 feet per minute to intercept the glide path. The autothrottle system entered the retard mode, and the thrust levers were moved to the idle position and remained in retard mode. Normally this mode is automatically engaged during landing flare just prior to touchdown. The glide path was intercepted at approximately 1330 feet and the aircraft was now also at the correct altitude for the approach of runway 18R. The aircraft speed had during the time the aircraft was in vertical speed modus increased to 169 knots, and decreased again when the aircraft followed the glide path.

At approximately 900 feet, the flaps were selected to 40 by the crew and the speed continued to decrease. At approximately 770 feet, the crew set the selected airspeed to 144 knots. At that moment the actual airspeed was 144 knots. The autothrottle system should have maintained the speed selected by the crew but, with the thrust levers at idle, speed continued to decay. Because the auto pilot wanted to maintain the glide scope, the automatic flight system, in response, commanded increasing nose up pitch and applied nose up stabilizer trim.

The stick shakers activated at approximately 460 feet, warning the crew that the angle of attack (AOA) was too high. The data of the digital flight data recorder show that the thrust levers were immediately advanced but moved back to idle. When the thrust levers returned to idle, the autothrottle was disengaged. Whether these actions were performed by the crew or automatically is still under investigation. At that moment, the speed was approximately 110 knots, the pitch angle was approximately 11° Aircraft Nose Up (ANU) and the recorded AOA was approximately 20°.

At 420 feet the autopilot was disengaged by the crew and attempts were made to recover the correct flight position by pitching the aircraft. At 310 feet a nose down angle was reached of 8° beneath horizon. Almost simultaneously the thrust levers were advanced to their most forward position after which the aircraft ascended somewhat and the nose position increased.

According to the last recorded data of the digital flight data recorder the aircraft was in a 22° ANU and 10° Left Wing Down (LWD) position at the moment of impact.

The airplane impacted farmland. The horizontal stabilizer and both main landing gear legs were separated from the aircraft and located near the initial impact point. The left and right engines had detached from the aircraft. The aft fuselage, with vertical stabilizer, was broken circumferentially forward of the aft passenger doors and had sustained significant damage. The fuselage had ruptured at the right side forward of the wings. The forward fuselage section, which contained the cockpit and seat rows 1 to 7, had been significantly disrupted. The rear fuselage section was broken circumferentially around row 28.

Weather reported about 09:40 UTC (10:40 local): EHAM 250925Z 20010KT 4500 BR SCT007 BKN008 OVC010 04/03 Q1027 TEMPO 2500= [Wind 200 degrees, 10 kts, visibity 4500m in mist, scattered clouds 700 ft., broken clouds 800 f, overcast 1,000 ft. Temperature 4 deg. C, Dew point 3 deg. C]

EHAM 250955Z 21010KT 4500 BR BKN007 OVC008 05/04 Q1027 TEMPO 2500=[Wind 200 degrees, 10 kts, visibity 4500m in mist, broken clouds 700 f, overcast 800 ft. Temperature 5 deg. C, Dewpoint 4 deg. C]

Findings

The Dutch Safety Board has reached the following main conclusion:
During the accident flight, while executing the approach by means of the instrument landing system with the right autopilot engaged, the left radio altimeter system showed an incorrect height of -8 feet on the left primary flight display. This incorrect value of -8 feet resulted in activation of the ‘retard flare’ mode of the autothrottle, whereby the thrust of both engines was reduced to a minimal value (approach idle) in preparation for the last phase of the landing. Due to the approach heading and altitude provided to the crew by air traffic control, the localizer signal was intercepted at 5.5 NM from the runway threshold with the result that the glide slope had to be intercepted from above. This obscured the fact that the autothrottle had entered the retard flare mode. In addition, it increased the crew’s workload. When the aircraft passed 1000 feet height, the approach was not stabilised so the crew should have initiated a go around. The right autopilot (using data from the right radio altimeter) followed the glide slope signal. As the airspeed continued to drop, the aircraft’s pitch attitude kept increasing. The crew failed to recognise the airspeed decay and the pitch increase until the moment the stick shaker was activated. Subsequently the approach to stall recovery procedure was not executed properly, causing the aircraft to stall and crash.