Investigators probing the fatal Dana Air Boeing MD-83 approach crash to Lagos face a substantial hurdle to explain an apparent dual-engine failure on the jet, after the badly-damaged flight-data recorder was unable to provide information.
The preliminary inquiry report into the 3 June accident, which killed all 153 occupants, states that while 31min of conversation was stored on the cockpit-voice recorder, the post-crash fire "melted" the medium of the flight-data recorder.
"Consequently no data could be recovered," says the Nigerian Accident Investigation Bureau.
The MD-83 had received 8,000lb of fuel at Abuja, according to records, and the crew had reported having total fuel of 26,000lb before departure.
Initial analysis of the fuel quality from the supply tank as well as the refuelling truck came back "negative for contamination", the bureau states.
Cockpit exchanges showed that, about half an hour before the crash, the pilots discussed an abnormal correlation between the throttle setting and the power indication of the Pratt & Whitney JT8D engines.
The crew became "increasingly concerned" as the aircraft descended from cruise altitude, but the situation only turned critical as the aircraft reached final approach to Lagos's runway 18R, with the slats, flaps and landing-gear deployed.
As the first officer asked, "Both engines coming up?", the captain responded: "Negative."
Less than a minute later, the crew issued a distress call citing dual engine failure and negative response from the throttle.
The pilots considered switching the approach to the parallel runway 18L, the offset threshold of which was closer. But the captain then reported the runway in sight and told the first officer to retract the flaps and the landing-gear - possibly to reduce drag.
Just over 40s later the captain told the first officer: "We just lost everything, we lost an engine - I lost both engines."
The crew spent 25s trying to restart the powerplants but the aircraft descended into a residential area about 5nm north of the airport. Only about 15% of the structure - including both engines, the empennage and sections of the wings - was retrieved for examination, as most of the jet was destroyed by fire.
Maintenance records show the aircraft's left and right engines had respectively logged around 54,300h and 26,000h since new but technical logs from the previous 30 days "did not indicate" any unusual conditions. The MD-83 had undergone maintenance on 1 June, two days before the accident, but had since conducted eight revenue flights.
Dana Air says that the twinjet had undergone an A-check on 30 May while a C-check was not due until September 2012. It maintenance is performed by Turkish organisation MyTechnic.
"Dual engine failure is a rarity and it could be as a result of several factors," it adds, but points out that the aircraft was maintained correctly and "fully in accordance" with the manufacturer's schedule and Nigerian regulatory directives.