What happened
On January 20, 2024, a Leonardo AW139 helicopter bearing registration 5N-BSG, operated by Caverton Helicopters Limited, departed Murtala Muhammed Airport in Lagos (DNMM) for a charter flight to the Bonga Floating Production Storage and Offloading (FPSO) vessel. The aircraft carried twelve individuals, including two crew members, under Instrument Flight Rules conditions.
Approximately twenty-six minutes into the flight, while cruising at 2,500 feet near the ETVOV waypoint, the Crew Alerting System triggered warnings indicating failures in both Automatic Pilot 1 and Automatic Pilot 2. The flight crew attempted to reset controls and re-engage the Automatic Flight Control System (AFCS) multiple times without success. Data from the Multi-Purpose Flight Recorder indicates that Autopilot 2 disengaged and re-engaged five times within a two-minute window.
After resetting the master generator switches, the autopilot failure persisted, causing the aircraft to drop its nose. The helicopter then exhibited unstable flight characteristics, climbing to 3,500 feet before plunging rapidly to 330 feet with significant pitch and roll variations. The captain assumed manual control while the first officer monitored instruments. Following several corrective maneuvers, the AFCS was successfully re-engaged, stabilizing the aircraft at 1,000 feet above ground level.
The crew decided to divert back to Lagos. The helicopter descended to 500 feet and landed safely at DNMM approximately two hours after departure. Upon disembarkation, it was confirmed that three passengers had sustained minor injuries, while the rest of the occupants were unharmed.
The investigation
The Nigerian Safety Investigation Bureau (NSIB) examined flight data, cockpit voice recordings, and crew statements to reconstruct the sequence of events. The bureau focused on the technical anomalies leading to the dual autopilot failure and the subsequent loss of altitude control. The investigation confirmed that Instrument Meteorological Conditions prevailed during the incident, highlighting the critical nature of the automation failure in low-visibility environments.
Findings
The primary established factor was the simultaneous failure of both autopilot systems, which led to erratic altitude and attitude changes. The crew's successful recovery relied on manual intervention after automated systems proved unreliable. The rapid descent to 330 feet represented a critical loss of controlled flight altitude before stabilization was achieved.
Safety action
The NSIB has completed the draft final report and submitted it for proofreading. Once finalized, the document will be circulated to relevant stakeholders for comments in accordance with ICAO Annex 13 requirements. This interim statement was issued on the second anniversary of the incident as mandated by international aviation safety protocols.