What happened
On January 24, 2025, at approximately 00:31 UTC, a Boeing 787-8, registration N27903, was operating as a scheduled international passenger flight from Lagos, Nigeria (LOS) to Washington Dull and International Airport (IAD). While cruising at 36,000 feet over Côte d'Ivoire airspace, the aircraft experienced a series of altitude excursions.
Flight data indicates that approximately one hour and five minutes before the excursions, the left inertial reference unit (IRU) failed. Roughly 55 minutes later, the right IRU also failed. At 00:30:57, the autopilot disconnected automatically, prompting the flight crew to take manual control. This event triggered the master caution and master warning systems. Three seconds later, the autothrottle disconnected, and a stick shaker activation was recorded at 00:31:14. The altitude excursions, which lasted approximately 12 minutes, saw the aircraft fluctuate between a minimum of 35,577 feet and a maximum of 36,203 feet msl.
During these fluctuations, meal service was being conducted in the cabin. The aircraft sustained minor damage, and while there were no fatalities, the event resulted in 1 serious injury and 15 minor injuries.
Following the event, the flight crew initiated an air turn back to Lagos. The autopilot was reengaged at 00:44:39 and remained active until the final approach into LOS. The aircraft landed uneventfully, and emergency responders transported the injured to a nearby clinic.
The investigation
The NTSB was granted delegation by the Bureau Enquêtes Accidents (BEA) Côte d'Ivoire to conduct the investigation. Flight recorders, IRUs, and attitude heading reference units (AHRUs) were recovered in Lagos and transported to the NTSB headquarters in Virginia for testing. While the flight data recorder was successfully downloaded, the cockpit voice recorder had been overwritten and could not be recovered for the period of the accident.
Parties to the investigation include the FAA, United Airlines, Boeing, Honeywell, and the Air Line Pilots Association (ALPA). The investigation is ongoing.