Investigation Summary
The accident occurred during a scheduled flight from Beijing to Ürümqi. As the MD-82 was established on final approach in conditions of approximately 1 km visibility due to fog, the autopilot automatically disconnected. The captain attempted to re-engage the autopilot, assuming it would resume following the ILS glide slope in approach mode. However, the system engaged in vertical speed (VERT SPD) mode with a pre-selected descent rate of 800 feet per minute. This commanded descent took the aircraft below the required glide path. As the aircraft neared the ground, the Ground Proximity Warning System (GPWS) triggered an aural 'Pull Up' alarm. Cockpit voice recordings revealed a critical language barrier: the captain asked the first officer for a translation of the warning, but the first officer admitted he did not know what the words meant. The crew failed to take corrective action or transition to a manual climb, leading the aircraft to strike obstacles and crash 3 km (approximately 1.8 to 2.2 miles) short of Runway 25.
Final Conclusions
The investigation concluded that the primary cause was Controlled Flight Into Terrain (CFIT) resulting from pilot error. Contributing factors included the crew's failure to monitor the autopilot's active mode after re-engagement, their failure to transition to manual flight when the automated approach became unstable, and a lack of English language proficiency that prevented them from understanding and reacting to life-saving GPWS alerts.
Photographic Evidence (1)
Video Analysis
MD-82 Crashes Just Before Landing: China Northern Airlines Flight 6901 — On 13 November 1993, an MD-82 registration B-2141 was trying to land under poor visibility, but the pilots' lack of English proficiency led to a fatal misunderstanding of GPWS warnings.
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Airframe & Maintenance
Systems & Failure Modes
Autopilot (Flight Guidance System)
The MD-82 autopilot can operate in various modes; when re-engaged without a specific lateral or vertical mode armed, it may default to basic modes like Vertical Speed, which in this case maintained a steady descent into the ground.
Ground Proximity Warning System (GPWS)
A system designed to alert pilots if their aircraft is in immediate danger of flying into the ground or an obstacle. It issued a 'Pull Up' command which the crew did not understand due to language barriers.
Interesting Facts
- 01The aircraft struck a wall with its rear fuselage approximately 3 km (1.8 miles) short of the runway.
- 02Visibility at the time of the accident was approximately 1 km in fog.
- 03The MD-82 involved (B-2141) was only two years old, having been delivered in December 1991.
- 0412 occupants were killed, while 90 survived the impact and subsequent fire.
- 05Approximately 60 people sustained injuries during the accident.
- 06The autopilot was set to a vertical speed of -800 feet per minute at the time of re-engagement.
- 07The aircraft's Manufacturer Serial Number (MSN) was 49849/1772.
Safety Actions & Advisories
English Language Proficiency Requirements
The accident highlighted the critical need for non-English speaking crews to understand standardized English aviation terms and emergency warnings used by Western-built avionics.