Investigation Summary
The investigation focused on why a highly experienced crew attempted a takeoff in a clean configuration. The Boeing 737-200 requires flaps and slats to be extended to at least 1 or 5 degrees for takeoff to provide the lift needed at rotation speeds. Wreckage analysis of the flap jackscrews confirmed they were in the fully retracted position at the time of impact. Furthermore, the Cockpit Voice Recorder (CVR) did not capture the sound of the takeoff configuration warning horn, which should have alerted the pilots as soon as the throttles were advanced. A critical discovery in the wreckage was the P5-11 circuit breaker, which provides power to the Take-off Warning System (TOWS); it was found in the open or 'popped' position. While investigators could not definitively prove if the breaker popped due to the impact or had been intentionally pulled or tripped prior to takeoff, its state explained why the crew was not alerted to their configuration error. The crew also failed to catch the error during their pre-takeoff checklists, indicating a significant breakdown in standard operating procedures and Cockpit Resource Management (CRM).
Final Conclusions
The NTSC concluded the primary cause was the aircraft taking off with an improper configuration (retracted flaps and slats). Contributing factors included the crew's failure to follow checklist procedures effectively and the failure of the takeoff warning system to alert the crew to the configuration error. The high death toll was exacerbated by the airport's proximity to a densely populated urban area, leading to significant ground casualties.
Photographic Evidence (1)
Video Analysis
Mandala 091: A Normal Morning… Until Throttles Advanced — A detailed reconstruction of the 2005 Medan crash, exploring the aerodynamic consequences of a flapless takeoff and the procedural failures in the cockpit.
If playback is blocked, the owner has disabled embedding — use the link above.
Systems & Failure Modes
Flaps and Slats
High-lift devices on the wings that must be extended to increase lift during low-speed operations like takeoff.
Take-off Warning System (TOWS)
An intermittent horn designed to sound if the throttles are advanced while the aircraft is not in a safe takeoff configuration.
Jackscrews
Mechanical components used to move flight control surfaces; their position in the wreckage proved the flaps were retracted.
Interesting Facts
- 01The crash killed the incumbent Governor of North Sumatra, Rizal Nurdin, and former Governor Raja Inal Siregar.
- 02Only 17 passengers survived the crash, while 100 occupants and 49 people on the ground perished.
- 03The aircraft was 24 years old and had accumulated over 51,000 flight hours at the time of the accident.
- 04Post-crash investigation found the flap lever in the 0-unit (retracted) position.
- 05The takeoff roll was noted by witnesses and survivors as being unusually long and shaky.
Safety Actions & Advisories
Checklist Discipline Reinforcement
Mandala Airlines was directed to improve flight crew training regarding the strict adherence to checklists and CRM.
Warning System Inspections
Recommendations were made to operators to ensure the serviceability of takeoff configuration warning systems through more rigorous maintenance checks.