Surprised this isn't here already, actually.
http://www.jacdec.de/2015/09/08/2015...stern-senegal/
On January 2016, the Senegal Bureau d’enquête et d’Analyse (BEA) reported an update to the current investigation process.
The Hawker HS-125 erroneously was flying at a level 1000 ft above their original clearance. ATC cleared the flight to 34.000 ft. (FL 340) but instead the pilots levelled of at 35.000 ft (FL 350) putting themselves on the same altitude as the opposite flying 737.
Air Traffic Control did not remind the pilots to correct their level nor did the pilots do any altitude changes before the collision took place.
The aircraft was involved in a mid-air collision with a smaller Hawker HS-125 business jet whilst flying over Senegal. The latter aircraft later crashed in sea killing all seven on board.
Ceiba flight CEL 71, a Boeing 737-800, was flying enroute at 35.000 ft, heading southeast on airway UA601, a few minutes east of Tambacounda VOR when it encountered opposite traffic at the same level.
The other aircraft was a Hawker HS-125 (registration 6V-AIM) opertated by Senegalair. This aircraft was on a medical flight from Ouagadougou to Dakar with four passengers (among them a patient) and three crewmembers.
It is understood that no reports about any conflict were transmitted to Bamako air traffic control. The controller later raised alarm when the HS-125 failed to answer to repeated calls.