Investigation Summary
The collision occurred in an area without radar coverage. The CEIBA Boeing 737 was correctly cruising at FL350, while the Senegalair HS-125 had been cleared to FL340. However, due to a long-standing and un-rectified fault in the HS-125's pitot-static system, the aircraft's altimeter displayed FL340 while the aircraft was actually at FL350. This discrepancy also prevented the Traffic Collision Avoidance System (TCAS) from functioning correctly, as the transponder was broadcasting the same erroneous altitude data, leading to a lack of resolution advisories for either crew. After the impact, which sheared off the top of the Boeing's winglet, the HS-125 became a 'ghost flight.' It is believed the collision caused a structural breach leading to hypoxia. The aircraft overflew Dakar at cruise altitude before crashing approximately 110km out to sea.
Final Conclusions
The BEA Senegal concluded the primary cause was the failure of the HS-125 crew to maintain their assigned flight level. A significant contributing factor was the failure of Senegalair maintenance staff to comply with established procedures regarding a known defect in the aircraft's altimetry system. Crucially, the aircraft was legally grounded at the time of the accident because the only technician authorized to sign the Approval for Release to Service had left the company on August 15, 2015. Additionally, the co-pilot's license had been validated without the required physical and mental fitness certificate, and the lack of radar coverage in the region prevented air traffic control from detecting the altitude deviation.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
CEIBA Intercontinental C2-71 — Boeing 737-8FB · 3C-LLY
Senegalair 6V-AIM — Hawker Siddeley HS-125-700A · 6V-AIM
Crew Experience
Captain
First Officer
License validated without required physical and mental fitness certificate.
Systems & Failure Modes
Pitot-Static System
The HS-125 system was faulty, causing the altimeter to under-read the actual altitude by 1,000 feet.
TCAS
Traffic Collision Avoidance System; failed to provide alerts because both aircraft appeared to be at different altitudes to the sensors.
Autopilot
Maintained the HS-125's heading and altitude for nearly an hour after the crew was likely incapacitated.
Interesting Facts
- 01The HS-125 was performing a medical evacuation flight with a French patient on board at the time of the collision.
- 02The HS-125 wreckage and its seven occupants were never recovered from the Atlantic Ocean.
- 03The victims on the HS-125 included three Senegalese, two Algerians, one Congolese, and one French national.
- 04The Boeing 737 suffered only a sheared winglet tip and was later repaired and returned to service.
- 05The HS-125 had been operating with a known defective altimeter for 10 days prior to the accident.
- 06No TCAS warnings were generated because the HS-125 transponder was transmitting the same erroneous altitude shown to the pilots.
- 07The collision occurred in the Dakar terrestrial Flight Information Region (FIR) in an area lacking radar surveillance.
Safety Actions & Advisories
Maintenance Oversight
The investigation highlighted the critical need for operators to ground aircraft with known altimetry discrepancies until verified repairs are completed.