ADC 737 stalled during clumsy windshear recovery

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Nigerian investigators have determined that an ADC Airlines Boeing 737-200 crashed on departure from Abuja after stalling as the pilots attempted to recover from windshear.

Only nine of the 105 occupants survived the accident which occurred just over a minute after the twinjet took off for Sokoto.

While the accident occurred on 29 October 2006 the Nigerian Accident Investigation Bureau has only just published its final report, one of a batch newly released by the authority.

Flight ADK053 had been advised of winds gusting up to 35kt while taxiing for runway 22, and a Virgin Nigeria flight communicated that it intended to wait for the weather to improve.

While the captain, who was flying, remarked to the first officer that they should be prepared for possible windshear, the ADC 737 proceeded to take off in heavy rain.

"From the weather report and the prevailing gusty wind, the trend would have required the crew to delay their departure, taking best practice and good airmanship into consideration," says the inquiry.

It rotated at 133kt, about 5kt below correct rotation speed for the configuration. Just 6s after the landing-gear was retracted a windshear warning triggered.

Boeing analysis indicates that headwinds experienced on rotation suddenly changed to tailwinds, contributing to a 25kt airspeed loss in 6s. The airspeed had reached about 162kt before quickly deteriorating.

Flight-data recorder information shows the crew initially pitched the nose down, then up to around 30-35°, says the inquiry, "greatly exceeding" the critical angle of attack. The stick-shaker activated and the engines suffered a compressor stall.

Control inputs by the crew led to an aerodynamic stall and the aircraft lost altitude. It banked more than 90° to the left and struck the ground, nose low, about 1,300ft off the runway end and some 2,600ft right of the centreline. It had been airborne for 76s.

Investigators determined that the aircraft "appeared to have enough energy" to fly through the adverse weather but that the pilots' reaction was "not in accordance" with windshear recovery procedures. This took the aircraft "outside the safe flight regime", the inquiry adds.

Examination of the crew's records showed that the captain had just 353h in command, even though he had logged over 8,500h. The first officer had nearly 6,500h but the inquiry notes that his record showed "a lot of discrepancies", including inconsistencies in his flight-time log. It adds that efforts to "clarify certain issues" regarding his air transport pilot's licence, issued in Guinea, were "unsuccessful".