Nigerian investigators have disclosed that the crew of a Dana Air Boeing MD-83 failed to take emergency action in response to a serious engine problem, apparently in fear of attracting attention from regulators, before the jet experienced dual-engine power loss and crashed on approach to Lagos.
The crew had been discussing a discrepancy in the thrust from one of the aircraft’s Pratt & Whitney JT8D engines early into the fatal flight from Abuja.
But the Nigerian Accident Investigation Bureau inquiry found that the MD-83 did not return to Abuja, and overflew several alternate airports – including Akure and Ibadan – where an emergency landing could have been made.
“At one time the pilot asserted that the aircraft could not quit on them,” says the inquiry into the 3 June 2012 crash. “At another time, the captain said declaring an emergency would make [the Nigerian Civil Aviation Authority] come after them.
“The delay to declare an emergency due to unexplained fear of the regulatory body compounded their problems.”
Both Pratt & Whitney JT8D engines failed to deliver commanded thrust during final approach to Lagos and the aircraft crashed with the loss of all 153 occupants as well as six people on the ground.
No flight-data recorder information was available to the Nigerian Accident Investigation Bureau and the inquiry has had to rely heavily on the cockpit-voice recorder.
The final inquiry report contains a confusing record of the accident sequence, particularly regarding the timing of events.
But it states that the cockpit-voice recorder captured some 30min of the flight and, at the point the recording started, some 16min after the jet was airborne, the pilots were already discussing an abnormal condition regarding the correlation between thrust setting and the engine power indication.
Audio spectrum analysis by US investigators and Pratt & Whitney has proven “inconclusive”, says the inquiry. “No definitive outcome was established.” It states that, while the problem started with the left-hand engine, no flame-out was established.
While the crew initially did not express concern about the condition in the engine, they became “increasingly” worried as the flight progressed, says the inquiry. But the crew neither declared an emergency nor called for the abnormal checklist to diagnose the problem.
During preparations for the approach, the crew confirmed there was no throttle response from the left engine, and the captain took over the controls. The crew opted for an approach to Lagos’ runway 18R but still did not transmit any distress call.
With confirmation of throttle response from the right engine, the anti-ice, ignition and bleed air were switched off. The crew received vectors from the radar controller and started configuring the MD-83 for landing, by deploying the flaps.
“Subsequently the problem became compounded as thrust was required to continue the final approach,” says the inquiry, pointing out that there was no evidence of an attempt to follow an engine-out descent profile. The landing-gear, it adds, was deployed after an audio alert from the ground-proximity warning system.
The aircraft increased its rate of descent as it passed 5,000ft some 15nm from Lagos. About 1min later the first officer asked whether both engines had “come up”, to which the captain responded: “Negative.”
Both engines at this point were failing to deliver the commanded thrust, says the inquiry, and the first officer asked the captain whether he should declare an emergency. The crew agreed to a distress call, transmitting: “Dual engine failure, negative response from throttles.”
“Though there was loss in engine power, there was no evidence of engine flame-out since the crew were able to select flaps, lower and retract the landing-gear as evident on the [cockpit-voice recorder transcript,” says the inquiry.
The radar controller instructed the flight to contact Lagos tower, but the crew was unable to select the tower frequency.
Investigators state that the crew discussed switching to runway 18L, offset further to the north, and the captain instructed a retraction of flaps and landing-gear. But the captain, having expressed concern about a possible stall, reiterated that he had “lost everything” and “lost both engines”, and called for various items – including “relight”, “ignition override” and “just anything” – which might help in the final moments of the flight.
Attempts to maintain altitude with manual control were unsuccessful, and automated warnings about the aircraft and the retracted landing-gear continued until impact in a densely-populated area some 8km north of the airport, on the approach centreline for runway 18R.
Investigators state that, while the engine power loss directly led to the crash, the crew’s “inappropriate omission” of checklist use and “inability to appreciate the severity” of the problem contributed to the failure to divert to an alternate airport.
