Investigation Summary
During the approach to runway 18R, the left radio altimeter (RA) suddenly provided a reading of -8 feet despite the aircraft being at approximately 2,000 feet. Because the autopilot was using the left RA data, the autothrottle system logic assumed the aircraft was in the flare phase of landing and retarded the throttles to idle. The crew, preoccupied with completing the landing checklist and managing a late intercept of the glideslope, did not notice the significant drop in airspeed. By the time the stick shaker activated, the aircraft had lost too much energy. The pilot's initial attempt to add thrust was momentarily countered by the autothrottle (which was still engaged and trying to keep the engines at idle), and the aircraft impacted a muddy field, breaking into three sections.
Final Conclusions
The Dutch Safety Board concluded the primary cause was a combination of a technical failure (faulty radio altimeter) and human factors (failure to monitor flight instruments). The autothrottle's reliance on a single, non-redundant radio altimeter input allowed a single point of failure to command an inappropriate engine response. The crew's failure to maintain a stabilized approach and their delayed reaction to the decaying airspeed were critical contributing factors.
Video Analysis
Analysis of Turkish Airlines Flight 1951 Crash at Schiphol Airport — This video examines how a faulty radio altimeter caused the autothrottle to prematurely reduce thrust, leading to an aerodynamic stall and crash during approach to Amsterdam in 2009.
Watch on YouTube ↗If playback is blocked, the owner has disabled embedding — use the link above.
Systems & Failure Modes
Radio Altimeter (RA)
Provides height above ground; the left RA provided a false -8ft reading, triggering landing logic prematurely.
Autothrottle
Automatically adjusted engine power to idle based on the false RA data, leading to a loss of airspeed.
Stick Shaker
A mechanical device that vibrates the control yoke to warn the pilot of an impending stall.
Interesting Facts
- 01The aircraft was a 7-year-old Boeing 737-800 named 'Tekirdağ'.
- 02All three pilots in the cockpit (Captain, First Officer, and a safety pilot) were killed.
- 03The aircraft broke into three pieces but did not catch fire, which significantly increased the survival rate.
- 04The left radio altimeter had failed in a similar manner on two previous flights.
- 05The autothrottle system on the 737-800 at the time did not compare data between the two radio altimeters.
Safety Actions & Advisories
Boeing Operations Manual Bulletin
Source ↗Boeing issued a bulletin reminding pilots to monitor airspeed and thrust, and to disconnect autothrottle if radio altimeter discrepancies occur.
Autothrottle Software Update
Boeing updated the autothrottle software to compare readings from both radio altimeters to prevent a single faulty sensor from retarding the throttles.
Known Controversies & Unanswered Questions
Allegations of Boeing Influence
Reference ↗A 2020 New York Times investigation alleged that Dutch investigators were pressured by Boeing and U.S. officials to downplay design flaws in favor of emphasizing pilot error.