Nigerian investigators have disclosed that an Allied Air Boeing 737-400 freighter carried out 85% of its landings with a ‘flaps 15’ setting in the six weeks before a gear-collapse and runway excursion at Abuja.
The inquiry into the 11 December accident is recommending that the carrier inspects its fleet for possible landing-gear and flap problems.
Allied Air’s aircraft (5N-JRT) was operating a positioning flight from Lagos to pick up cargo for the Central Bank of Nigeria. No cargo was on board at the time.
But when the crew selected ‘flap 30’ during approach to Abuja’s runway 22, the flaps did not extend beyond the ‘flap 15’ position.
The crew opted to continue the approach because the aircraft’s weight was within limits. At this point the jet was around 0.6nm from the runway, and was cleared to land.
Flight-data recorder information shows the jet touched down at 157kt.
According to the Nigerian Safety Investigation Bureau, the crew testified that the touchdown was smooth.
But shortly afterwards, it says, they heard a bang and the aircraft “collapsed” to the right, as its right-hand main landing-gear separated.
The nacelle of the right-hand engine contacted the runway and scraped the surface for nearly 1,200m before the aircraft veered off to the right.
It came to rest in the grass verge, 54m from the runway edge, having turned almost fully to face the opposite direction.
All six occupants evacuated the aircraft through the forward exit without injury.
Inspection of the aircraft “did not reveal evidence of a hard landing”, says the Safety Investigation Bureau.
But analysis of flight-data recordings showed that, over the six weeks between 1 November and the day of the accident, 85 of the aircraft’s 101 landings had been carried out with a ‘flap 15’ setting.
The other 16 landings had used ‘flap 25’.
While the safety bureau has yet to reach final conclusions over the occurrence, it has issued a recommendation for Allied Air to inspect all its aircraft for “potential mechanical and structural vulnerabilities”, including their flap and landing-gear systems.
Further analysis is to be undertaken on the aircraft involved in the accident, including detailed inspection of the right-hand main-gear assembly and the flap-drive system components.
