What happened
On the day of the accident, a flight originating from Saint Louis was cleared for descent toward Dakar-Yoff Airport. The crew received instructions to hold an altitude of 3,000 feet while positioned over the YF VOR. Simultaneously, a scheduled Gambia Airways flight, a NAMC YS-11A-117 with registration C5-GAA, was departing Dakar-Yoff Airport for Banjul. The crew of the NAMC aircraft was directed to climb using radial 140 and maintain an altitude of 2,000 feet while passing over the same YF VOR waypoint.
As both aircraft reached the YF VOR, they collided in mid-air. The NAMC YS-11A-117 sustained damage, including a partially torn left wing, but the crew managed to perform an emergency return to Dakar-Yoff Airport and land without further incident. However, the Twin Otter aircraft entered an uncontrolled descent following the impact and crashed into the ocean a few kilometers from the coast. The accident resulted in three fatalities among the occupants of the Twin Otter.
Findings
Investigations into the collision revealed that both flight crews failed to adhere to their assigned altitudes. Specifically, the Twin Otter was flying approximately 100 to 300 feet below its designated level, while the C5-GAA was operating roughly 700 to 900 feet above its instructed altitude. The primary cause of the collision was the failure of both crews to maintain their assigned altitudes.