Preliminary information from cockpit voice recorders and flight data recorders on an Associated Aviation Embraer EMB-120 turboprop that crashed on departure from Lagos on Oct. 3 show that the captain continued the takeoff roll despite engine and flap issues.

According to the Nigeria’s Accident Investigation Bureau (AIB), the aircraft “slowly veered off the runway heading to the right and was not climbing.” Ten sec. later, the stall warning sounded and continued to sound until the aircraft impacted the ground in nose-down, 90-deg. right bank attitude. “The flight data shows characteristics consistent with aerodynamic stall,” says the AIB in the new report.

The crash killed at least 16 of the 20 people on board, including four state officials who were flying to the funeral of a former regional governor being carried in a coffin in the cargo hold. Aviation Week’s Fleets database shows that Associated Aviation has two Pratt & Whitney Canada PW100-powered EMB120ERs in its eight-aircraft fleet.

Why the pilot departed despite warnings from onboard systems and the first officer is among the topics the AIB continues to pursue, along with mechanical and electronic control issues with the right engine.

According to the recordings, an automated warning (“Take-off Flaps, Take-off Flaps”) sounded 4 sec. after the pilots of Flight 361 applied takeoff power on Lagos Runway 18. The AIB says there is “some evidence” the crew was not using flaps for the departure and that the warning “did not appear to come as a surprise.” Seven sec. after the takeoff roll began, the automated system added “Auto Feather” to the continuing “Take-off Flaps” message, indicating that one of the propellers was in the “feather” position, a mode that is used to reduce drag after an engine fails.

The AIB says the right engine was producing “considerably less thrust” than the left, which was operating normally. Reduced thrust on the right engine may also explain why the aircraft veered to the right after departure. Investigators after the crash found that the right engine’s fire handle was pulled or activated and propeller was in the feathered position.

As the aircraft slowly accelerated to 95 kt. airspeed on the runway, the AIB says the first officer asked the captain if the takeoff should be aborted. The captain, however, indicated that the takeoff should be continued. The crew later did not make the normal “V1” and “Rotate” call-outs.

“During the rotation, the First Officer stated ‘gently,’ which we believe reflects concern that the aircraft is not performing normally and therefore needs to be rotated very gently so as not to aerodynamically stall the aircraft,” says the AIB. “The First Officer indicated that the aircraft was not climbing and advised the captain who was flying not to stall the aircraft.”

The AIB says Canadian flight recorder experts, who designed the new laboratory used to playback the audio and data recorders, assisted with the readout and analysis process along with representatives from Embraer and the airline.