What happened
On May 15, 1960, a Douglas DC-4, registration HB-ILA, operated by Balair, crashed into the slopes of Mt. Marra in the Darfur province of Sudan. The aircraft was performing a positioning flight from Jeddah to Dakar, with a scheduled stop in Khartoum.
After arriving in Khartoum with a delay, the captain decided to proceed immediately to Niamey and Dakar rather than taking the planned twelve-hour rest period. The flight departed Khartoum at 19:26 GMT. While the flight plan anticipated a headwind, the aircraft actually encountered a significant tailwind. The crew had planned to maintain an altitude of 8,000 ft for most of the route, increasing to 12,000 ft to clear the Mt. Marra massif, which features peaks exceeding 10,000 ft.
At approximately 19:57 GMT, while flying in darkness at 8,000 ft, the aircraft struck a mountainside approximately 6 NM east-northeast of the Mt. Marra summit. The impact and subsequent fire destroyed the aircraft, killing all 12 occupants, including the crew, several off-duty crew members, and two passengers.
The investigation
Following an initial inquiry by a Sudanese commission, the Swiss Federal Aircraft Accident Investigation Commission conducted its own investigation. The inquiry examined the aircraft's technical condition, the meteorological data, and the crew's operational decisions.
Investigators analyzed the navigation logs, which showed that a position report sent at 19:06 GMT suggested the aircraft would reach the El Fasher radio beacon at 20:01 GMT. However, the investigation determined that this report was inaccurate due to the unexpected tailwind. The investigation also reviewed the crew's fatigue levels, noting that the captain had been on duty since the previous day, and the navigators and co-pilots had also been working since the previous evening without sufficient rest.
Findings
- The primary cause of the accident was controlled flight into terrain while flying under instrument conditions at an insufficient safety altitude.
- The crew failed to initiate a climb to the required 12,000 ft altitude in a timely manner to clear the terrain.
- Inaccurate navigation occurred because the crew relied on a flight plan that did not account for the actual tailwind conditions.
- The decision by the captain to continue the flight immediately after arriving in Khartoum, violating established rest requirements, likely led to crew fatigue.
- There was a lack of precision in flight planning and navigation monitoring by the crew.