TURKISH AIRLINE TK 1951:
|TK 1951, Embedded fromAirline Safety.Net on 09 October 2010||TK 1951, Embedded fromAirline Safety.Net on 09 October 2010|
HISTORY OF THE FLIGHT:
This was a Boeing 737 – 800 which departed Istanbul International Airport for Amsterdam Schiphol International Airport. The crew consisted of a line training captain, a first officer under supervision and a safety first officer. The first officer under supervision was the pilot flying.
The accident occurred on approach into Amsterdam. The aircraft was radar vectored for runway 18R by air traffic control for an ILS approach. The vectors given lined the aircraft up for a 6 NM approach at 2000 feet. This meant that the aircraft would intercept the glideslope from above. The crew selected gear down and flap 15. As the aircraft descended past 1950 feet, the radio altimeter value changed to – 8 feet sounding the gear warning.
Once the crew had intercepted the localiser, they elected to select vertical speed mode for a rate of 1400 feet per minute to increase their rate of descent. The autothrottle entered retard mode and remained in retard mode. This meant that the thrust levers were at idle. This mode is normally engaged automatically during the landing flare stage, prior to touchdown.
The aircraft intercepted the glideslope at 1330 feet. At 900 feet, the landing flap (flap 40) was selected. At 770 feet, the crew selected the approach speed of 144 knots. The autothrottle system which should have engaged and maintained the airspeed continued to remain at retard mode, leaving the thrust levers at idle. To maintain the glideslope, the aircraft’s autopilot commanded a nose up attitude.
The stick shakers (stall warning) activated at 460 feet, warning the crew of an impending stall. The first officer reacted and moved the thrust levers forward. He, however, stopped at the mid range as the captain announced that he has control. In the transition, the thrust lever moved back to idle and disengaged. The speed of the aircraft was 100 knots, pitch angle of 11 degrees nose up and a bank angle of 20 degrees.
Nine seconds after the activation of the stick shaker, the captain moved the thrust lever full forward. The aircraft remained stalled and the height remaining, 350 feet, was insufficient for a recovery. The aircraft struck terra firma at a 22 degree nose up and 10 degree left wing down attitude.
Five passengers, a flight attendant and the three flight crew were killed. Three flight attendants and 117 passengers were injured.
ANIMATION OF TK 1951:
|(Video embedded from YouTube on 09 October 2010)|
INSIDE TK 1951 AFTER THE CRASH:
|(Video embedded from YouTube on 09 October 2010)|
FACTORS CONTRIBUTING TO THE ACCIDENT:
AIR TRAFFIC CONTROL:
The radar vectors given by air traffic control resulted in a “short line up”: This didn’t allow the crew to intercept the glideslope from below in level flight, as required by both ICAO and Netherlands ATC standards. This ultimately resulted in the increased workload of the crew.
LACK OF TECHNICAL KNOWLEDGE:
The flight crew attempted to engage the left autopilot. It would not engage and the right autopilot disengaged. This was due because the autopilots would only engage if the ILS frequency was tuned and the approach mode was armed – which was not. They managed to engage the right autopilot again. They flew the approach with only one autopilot – contrary to the procedures of the airline.
LACK OF MONITORING:
There was a lack of monitoring of the part of the captain as pilot monitoring:
- He failed to challenge and correct the pilot flying when he announced “second autopilot engaged” – when there was only one autopilot.
- He didn’t make the required callouts on approach, including changes in the flight mode annunciations.
All the crew were busy completing the landing checklist. As a result, no one noticed the change in the autothrottle mode “RETARD” and the reduction in airspeed. They also failed to notice the high nose up attitude of the aircraft on approach.
NON COMPLIANCE TO SOP:
Turkish airlines SOP requires a go around if the aircraft is not configured for landing and the landing checklist is not completed by 1000 feet above runway touchdown elevation. In this regard, all crew members failed to call for and conduct a go around.
The captain failed to conduct the appropriate actions for a stall recovery. He only applied full power nine seconds after the stick shaker activated.
The left radio altimeter, being the primary source of the height measurement for the autothrottle, started providing erroneous data after departure from Istanbul. It displayed – 8 feet passing 2000 feet on the ILS. This prompted the autothrottle to change to “retard” mode and reduced the thrust to the approach idle setting from 2000 feet. This phase is normally activated at 27 feet.
This was a known problem but Turkish Airline dealt with it as a technical problem and not a safety issue. As a result, the flight crew were not aware of the issue.
There was a warning for despatch that the autopilot/ autothrottle must not be used for approach/ landing if the associated radio altimeter is found defective. There was, however, no information/ guidance for the flight crew for occurrences inflight.
The final report by the Dutch Safety Board concluded that the accident was the result of the "convergence of circumstances" which included ATC's handling that brought the aircraft in high and close to the runway, the malfunction of the left radio altimeter and the flight crew's non compliance to SOP - their dismissal of indications that required a go around.
TK 1951. Retrieved 09 October, 2010 from http://www.onderzoeksraad.nl/docs/rapporten/Rapport_TA_ENG_web.pdf.
Turkish Airline 1951. Retreived 09 October, 2010 from http://en.wikipedia.org/wiki/Turkish_Airlines_Flight_1951.
Want to know more?
Final report TK 1951: http://en.wikipedia.org/wiki/Turkish_Airlines_Flight_1951.