According to Radio France Internationale (RFI), a near-miss between an A/C from Equatorial Guinea en route to Cotonou (but flew back to Malabo after the near-miss) and the Senegalair A/C chartered by SOS Médecins would have led the latest to loose cabine pressure, incapacitating everyone on board (since no radio-contact could be established after the near-miss). Which would explain why the plane crashed 111 Km westward from Dakar after fuel exhaustion. No source named by RFI.
Link :
Sept morts dans le crash d'un avion sanitaire au large du Sénégal - Afrique - RFI