Indonesian investigators on Wednesday said the Lion Air 737 MAX jet that crashed into the Java Sea last month was not in an airworthy condition even on its second-to-last flight, when pilots experienced similar problems to those on its doomed last journey.
In a preliminary report, Indonesia’s transport safety committee (KNKT) focused on the airline’s maintenance practices and pilot training and a Boeing Co anti-stall system but did not give a cause for the crash that killed all 189 people on board.
The report unveiled fresh details of efforts by pilots to steady the 737 MAX jet as they reported a “flight control problem”, including the captain’s last words to air traffic control asking to be cleared to “five thou” or 5,000 feet.
Information retrieved from the flight data recorder showed the “stick shaker” was vibrating the captain’s controls warning of a stall throughout most of the flight. The captain was using his controls to bring the airline’s nose up, but an automated anti-stall system was pushing it down.
Pilots flying the same plane a day earlier had experienced a similar problem, en route from Denpasar, Bali, to Jakarta, until they used switches to shut off the system and used manual controls to fly and stabilize the plane, KNKT said.
“The flight from Denpasar to Jakarta experienced stick shaker activation during the takeoff rotation and remained active throughout the flight,” the report said. “This condition is considered as un-airworthy condition” and the flight should have been “discontinued”.
The pilots of that flight reported problems to Lion Air’s maintenance team, which checked the jet and cleared it for take-off on the doomed flight the next morning.
After the crash, Lion Air instructed pilots to provide a “full comprehensive description” of technical defects to the engineering team, KNKT said.
In a statement, Boeing drew attention in detail to a list of airline maintenance actions set out in the report but stopped short of blaming ground workers or pilots for the accident.
The company, which has said procedures for preventing an anti-stall system activating by accident were already in place, said pilots of the previous flight had used that drill but noted the report did not say if pilots of the doomed flight did so.
Boeing’s statement did not make any reference to a revised anti-stall system introduced on the 737 MAX which U.S. pilots say and Indonesian investigators say was missing from the operating manual.
Boeing says the procedure for dealing with a so-called runaway stabilizer, under which anti-stall systems push the nose down even when the plane is not entering a stall or losing lift, had not changed between earlier version of the 737 and the newly delivered 737 MAX.
Pilots however say the control column behaves differently in certain conditions, which could confuse pilots who have flown the earlier model.
The Chief Executive Officer of Lion Air, Edward Sirait, said he had not yet read the KNKT report but will comply with all of the investigators’ recommendations.
The report provided new recommendations to Lion Air on safety on top of earlier recommendations about the flight manual that have already been implemented by Boeing.