The pilots of the Ethiopian Airlines 737 MAX that crashed last month initially followed Boeing emergency procedures but later deviated from them as they tried to regain control of the aircraft, the Wall Street Journal said.
The crash killed all 157 people on board and led to a global grounding of 737 MAX jets and scrutiny of the certification process for the Boeing jetliner.
Boeing issued guidelines to pilots on how to disable an automated anti-stall system after a deadly crash in Indonesia in October, followed by an emergency airworthiness directive from the US Federal Aviation Administration (FAA).
The Journal report, citing unidentified people briefed on the issue, said pilots initially shut off the MCAS anti-stall system pushing the airplane’s nose down shortly after take-off from Addis Ababa.
The pilots then cranked a manual wheel in an attempt to stabilise the aircraft, the report said, but decided to restore power to the normal electric trim on the control yokes, likely because the manual attempt did not work properly.
Reuters could not immediately verify the report. Boeing declined to comment.
“We are not commenting on an active accident investigation per international protocols,” a Boeing spokesman said.
The aircraft manufacturer said a proposed software enhancement package to MCAS would be submitted in “coming weeks”, having previously said it would deliver the fix for US approval by last week.
A 737 pilot told Reuters it was “not physically easy to make large trim changes to correct, say, an MCAS input” by using the wheel.
“You – or more than likely the other pilot – have to flip out a handle and wind, much like a boat winch,” the pilot said.
The Ethiopian Airlines pilots appeared to have restored power to the electric system to cope with a persistent steep nose-down angle, the paper said.
Their actions reactivated MCAS and allowed it to continue strong downward commands they were unable to counteract using electric thumb switches, the paper said.
The FAA directive after the Indonesian crash instructed pilots to use cut-out switches in the centre console to shut off electric power to the system.
The switches should remain off for the remainder of the flight, the FAA directive said.
A preliminary report by Ethiopian investigators is due within 30 days of the March 10 disaster, according to international rules governing crash investigations.