A Lion Air jet that crashed into the sea off Indonesia last month was not in an airworthy condition on its second-to-last flight when pilots experienced similar problems to those on its doomed last journey, investigators said on Wednesday.
In a preliminary report, Indonesia’s transport safety committee 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 Oct. 29 crash that killed all 189 people on board.
KNKT investigator Nurcahyo Utomo said the agency had not determined if the anti-stall system, which was not explained to pilots in manuals was a contributing factor.
“We still don’t know yet, if it contributed or not,” he said in response to a question. “It is too early to conclude.”
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.
Contact with the jet was lost 13 minutes after it took off from the capital, Jakarta, heading north to the tin-mining town of Pangkal Pinang.
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 plane’s nose up, but an automated anti-stall system was pushing it down.
“It’s very distracting and unnerving,” former Boeing flight control engineer Peter Lemme said of the stick shaker activation.
“It’s not something you ever want to have happen as a pilot.”
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 committee 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 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 manufacturer, which has said procedures for preventing an anti-stall system activating by accident were already in place, said pilots of the penultimate 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 and Indonesian investigators say was missing from the operating manual.
Boeing says the procedure for dealing with a so-called runaway stabiliser, 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.
A source at the U.S. Federal Aviation Administration said a number of factors were ultimately likely to be cited as causes of the crash, including pilot training and maintenance.
It had still to be determined how much, if at all, the plane design would be faulted, the source told Reuters on condition of anonymity.
Edward Sirait, chief executive of Lion Air, said he had not read the KNKT report but would comply with 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.
Authorities have downloaded data from one of the black boxes found days after the crash, the flight data recorder, but are still looking for the cockpit voice recorder (CVR).
Indonesia plans to bring in a ship from Singapore able to stay in position without dropping anchor, to help with the search.
Asked what was needed from the CVR, Utomo said: “A lot.
Discussions between the left and right pilots were about what? What procedures did they carry out. Were there any strange noises?”
Without it, he said there would be “a lot of guessing”.
Edited by: Udochukwu Ifionu/Silas Nwoha