The pilots of a Lion Air plane that crashed into the sea shortly after take-off struggled to fly the jet because some of the aircraft’s automated systems had not been working properly for days and the airline failed to ground the plane to repair the problem, according to a preliminary report by Indonesian investigators into last month’s crash that killed 189 people.
In a statement, Indonesia’s transport safety committee (KNKT) recommended that Lion Air improve its safety culture following the crash of the almost-new Boeing 737 MAX 8.
The MAX 8, the latest version of the 737, includes an automated system that pushes the nose down if a sensor detects it is pointed so high the plane is at risk of an aerodynamic stall.
Investigators are focusing on whether faulty information from sensors led the plane’s system to force the nose down.
Speaking from Jakarta, Al Jazeera’s Step Vaessen said the plane had been causing problems for pilots for four days previously.
“There were a lot of technical issues with the same plane,” she said, adding that the main problem was that the so-called ‘angle of attack’ indicator did not appear to be working properly.
“The pilots (on the earlier flights) turned this off and flew manually. But on the fatal flight, the pilots made a different decision. They didn’t fly manually.”
‘No longer airworthy’
Given the difficulties, Lion Air should not have been flying the plane, Nurcahyo Utomo, aviation head of the National Transport Safety Committee, told reporters.
“During the flight from Denpasar to Jakarta (the last flight before the crash), the plane was experiencing a technical problem, but the pilot decided to continue the flight,” he said.
“In our opinion, the plane was no longer airworthy and it should not have continued flying.”
The committee acknowledged actions to improve safety had been taken by Boeing, Lion Air, the U.S. Federal Aviation Administration and Indonesia’s Directorate General of Civil Aviation.
The New York Times reported earlier that information from the Lion Air jet’s flight data recorder was included in a briefing for the Indonesian parliament and reported by Indonesian media.
Indonesia: ‘No survivors’ after Lion Air flight crashes into sea
‘Deadly game of tag’
Peter Lemme, an expert in aviation and satellite communications and a former Boeing engineer, described “a deadly game of tag” in which the plane pointed down, the pilots countered by manually aiming the nose higher, only for the sequence to repeat about five seconds later.
That happened 26 times, but pilots failed to recognise what was happening and follow the known procedure for countering incorrect activation of the automated safety system, Lemme told The Associated Press.
He said he was also troubled that there weren’t easy checks to see if sensor information was correct, that the crew of the fatal flight apparently wasn’t warned that similar problems had occurred on previous flights, and the Lion Air plane wasn’t fixed after those flights.
“Had they fixed the airplane, we would not have had the accident,” he said. “Every accident is a combination of events so there is disappointment all around here.”
Boeing did not immediately respond to requests for comment.
The company said last week it remains confident in the safety of the 737 MAX and had given airlines around the world two updates to “re-emphasise existing procedures for these situations”. The US regulator has also issued a directive on the MAX 8 and 9 models.
More than 200 MAX jets have been delivered to airlines around the world.
The investigation is continuing with help from US regulators and Boeing.
The plane’s cockpit voice recorder, which would provide more information about what happened in the cockpit, has yet to be found.
Al Jazeera and news agencies