Niamey

The crew continued the approach in a reduced visibility due to blowing sand and descended too low without visual contact with the ground.

It is believed that the in-flight smoke and fire was the consequence of an electrical short-circuit.

The primary cause of this accident, in my opinion, was GAF 074 flying a cruise level (FL350) which was not the level they had filed for (FL390). Neither FL350 nor FL390 were the correct cruise levels for that aircraft's magnetic heading according to International Civil Aviation Organization regulations. The appropriate cruise level would have been FL290, FL330, FL370, FL410, etc. A substantially contributing factor was ATC agency Luanda's poor management of air traffic through its airspace. While ATC communications could be improved, ATC agency Luanda did have all the pertinent information it needed to provide critical advisories to both aircraft. If ATC agency Luanda was unable to contact GAF 074, it should have used other communication means (HF radio, telefax or telephone) to contact REACH 4201 through ATC agency Windhoek, as outlined in governing documents. Another substantially contributing factor was the complicated and sporadic operation of the Aeronautical Fixed Telecommunications Network (AFTN). Routing of messages to affected air traffic control agencies is not direct and is convoluted, creating unnecessary delays and unfortunate misroutings. Specifically, ATC agency Windhoek did not receive a flight plan or a departure message on GAF 074, which could have been used by the controllers to identify the conflict so they could have advised REACH 4201. In my opinion, the absence of TCAS was not a cause or substantially contributing factor, but the presence of a fully operational TCAS could have prevented the accident." (William H.C. Schell, jr., Colonel, USAF President, Accident Investigation Board).

It was reported that two engines were on fire when control was lost on approach.

Loss of control after landing due to strong crosswinds in thunderstorm activity.

The crew continued the approach below the glide until impact with ground.

It was determined that the accident was the consequence of the combination of the following factors:
- The fact that the aircraft progressed actually at an average ground speed of at least 200-205 knots while the crew believed they were proceeding with no more than 175-178 knots as estimated before takeoff,
- That a slight directional difference of 2 or 3 degrees may have existed between the calculated track and the actual flight path,
- That these two navigation inaccuracies could build up during a flight of 2,5 hours and could eventually result in a position error of about 70 NM to the west and about 30 NM to the south,
- That for reasons unknown to the Board the position report given for 1906Z and apparently established on the base of an astronomical fix must have been inaccurate and that the crew were, therefore, not able to be conscious of the discrepancies between the dead-reckoning and their actual position,
- That the aircraft flying at 8000 feet hit a slope of the Djebel Marra mountains four minutes before the crew expected to be overhead the El Fasher beacon where they would have begun the climb to 12000 feet and when, in their belief the aircraft should have been still more than 60 NM away from these mountains.

It was determined that the collision with the mountain was caused by a navigation error on part of the flying crew who decided, four minutes after takeoff from Douala Airport, to abandon the current procedure and followed a different route. The crew failed to follow the prescribed flight plan and to check the improvised route. Error of judgement and overconfidence on part of the crew were considered as contributory factors.