By Dickson Omobola

United States National Transportation Safety Board, NTSB, has said the navigation system of United Airlines flight UA613, which departed from Lagos to Washington in January, failed.

NTSB investigators, in its preliminary report, found that the navigation system’s failure resulted in the plane’s autopilot disengaging, thereby causing “altitude excursions.”

The report said approximately one hour and five minutes before the incident, inflight data indicated a failure in the left inertial reference unit, IRU, and about 55 minutes later, a failure in the right IRU was reported.

According to the report, flight data recorder information also showed that at 00:30:57, the autopilot disconnected automatically, prompting the flight crew to take manual control, which triggered both the master caution and master warning alerts.

The investigators noted that at that time, altitude excursions began and three seconds later, the autothrottle disconnected.

The NTSB report stated that at 00:31:14, a stick shaker activation was recorded. 20 seconds after that, the autopilot was reengaged for one second, then disconnected automatically again.

It added: “At 00:40:30, the aircraft started a right turn back toward Lagos. At 00:44:39, the autopilot was reengaged and remained engaged until the final approach to LOS Airport. The altitude excursions from 36,000 feet lasted approximately 12 minutes.”

On January 23, United Airlines flight UA613, outbound Lagos to Washington declared an emergency and returned to Lagos in the early hours of Friday.

The flight, which had 245 passengers, eight flight attendants and three pilots, made a direct return to the Murtala Muhammed International Airport, MMIA, while outbound in Ivory Coast airspace.