Investigators believe a Bellview Boeing 737-200 which crashed after taking off from Lagos should not have been cleared to fly, but have been unable to determine the cause of the fatal accident.
The inquiry uncovered improper technical logbook entries as well as defects that were ignored or inappropriately deferred - including two fuel-flow indicators which had been unserviceable for more than a week before the crash.
Nigeria's Accident Investigation Bureau, in its belatedly-published report into the 22 October 2005 event, says: "The [aircraft] should not have been dispatched for either the accident flight or earlier flights."
Flight B3210 departed runway 18L and turned right in order to head northeast to Abuja. After the crew acknowledged a request to report passing flight level 130, there was no further contact and no distress call.
None of the 111 passengers and six crew on board the aircraft (5N-BFN) survived.
Neither the flight-data nor cockpit-voice recorder was retrieved from the crash site, 14nm north of Lagos airport. Nigeria's Accident Investigation Bureau has not given a reason for the failure to recover them, but says it communicated several times with the police over the matter.
"[Investigators] did not, at any time, sight, handle or possess the flight recorders," it adds. Without them, the inquiry was badly obstructed. Despite "extensive" analysis, investigators "could not identify conclusive evidence" to explain the crash.
Even simple facts, such as the precise time of the accident or the flying pilot, could not be determined.
Inconsistencies in the captain's flight record also attracted the investigators' attention. He had not flown for 12 years before undertaking a 737 pilot-in-command training course in the USA in August 2004, and joining Bellview two months later.
Investigators found he logged 1,053h on type, all within just one year of employment with the airline - indicating "considerable work overload" and possible vulnerability to fatigue, says the inquiry. In the 10 months preceding the crash, it adds, his overall flight time exceeded 1,860h, a "gross violation" of duty limits.
Although Bellview submitted records to the inquiry showing the captain had accumulated a total of 11,053h. But Nigerian Civil Aviation Authority data suggest a substantially different figure of more than 13,400h.
He was cleared to command 737s for Bellview in November 2004. But the inquiry says his training was "inadequate" and that, with just 47h, he "did not meet" the airline's minimum requirement of 500h to serve as pilot in command on the type.
US National Transportation Safety Board investigators examined the thrust-reverser actuators and rudder power control unit but determined that they did not contribute to the accident.
Despite analysis from the FBI ruling out explosives, Bellview Airlines argued that sabotage could not be dismissed as a possible cause. But the inquiry criticised the airline's inability to keep its aircraft airworthy and branded Nigerian regulatory oversight of the carrier as "inadequate".