Nigeria, Oct. 17 -- The Nigerian Safety Investigation Bureau (NSIB) has begun an investigation into an incident involving a foreign-registered aircraft operated by Triton Aviation after the airline's crew reported that a door of the aircraft opened mid-air shortly after taking off from Abuja on Thursday.

The Challenger 604 aircraft, with registration number T7-SEI, departed the Nnamdi Azikiwe International Airport on Thursday for Lagos.

It was about three nautical miles from the airport, climbing through 3,500 feet, when its crew declared a Mayday emergency, according to the NSIB.

The aircraft returned to Abuja and landed safely on Runway 22 at 16:34 Coordinated Universal Time (UTC), with nine people on board, comprising three crew mem...