Officials inspect an engine recovered from the crashed Lion Air jet in Jakarta.
A malfunctioning sensor and an automated response from the aircraft's software stymied pilots' efforts to control a doomed Indonesian flight that went careening into the sea, a preliminary report released by investigators found Wednesday.
The report, which stops short of determining the cause of the crash or analysing findings, chronicles the chaotic moments on the Lion Air flight before it crashed into the sea, killing all 189 on board.
It details how sensors and other equipment were checked and fixed before the aircraft's final flight - but not the "angle of attack" sensor, which measures where the nose is pointing and was showing erroneous readings throughout the short time the plane was airborne.
With the sensor insisting the nose was too high, an automatic feature kicked in sending the plane plunging downward as the pilots wrestled to regain control. Unable to trust their readings, the pilots resorted to asking air traffic control what their speed and altitude were.
Lion Air Flight 610 plunged into the Java Sea on October 29 just after taking off from the Indonesian capital Jakarta, killing the eight crew members and 181 passengers on board, including a child and two infants.
The crash appears to have been caused by a mix of brand-new technology and cockpit confusion as the pilots fought to gain altitude after an early-morning takeoff from Jakarta.
The flight crew - at an altitude of just 5000 feet - had very little time to resolve the issue before the plane crashed into the Java Sea at a reported 450 miles per hour.
The aircraft's pilots asked to return to Jakarta just two minutes after takeoff, reporting a "flight-control problem" but didn't specify what it was.
Black box data released by Indonesian investigators showed that the pilots were pulling back on the control column, attempting to raise the plane's nose, with almost 100 pounds of pressure before they crashed.
The Indonesian National Transportation Safety Committee, which produced the report, also noted that the Jakarta-based low-cost airline, Lion Air, should improve its "safety culture".
The committee's report said the pilot should discontinue any flight where mechanical, electrical or structural problems occur.
No engineer briefed the pilot of the crashed plane on the multiple problems the aircraft experienced on previous flights, and it had been up to him to review the maintenance logs on-flight.
The report, however, contains no conclusion on who is at fault.
"When it comes to faulting, I don't know, our job isn't to find faults," National Transportation Safety Committee investigator Nurcahyo Utomo said at a news conference Wednesday.
The aircraft was the most recent incarnation of the venerable Boeing 737, a plane that first flew in 1967 and has gone through multiple iterations before it emerged as the 737 Max.
The 737 Max was equipped with more powerful engines that are mounted farther forward on the wing, requiring additional software be added to the autopilot to provide more control.
That software, which has been described as several lines of coding, was identified in the Boeing manual as the maneuvering characteristics augmentation system, or MCAS.
When the sensors transmitted faulty data to the cockpit of Flight 610, the new MCAS system sensed a stall - that point at which a plane is so vertical that it is in danger of falling from the sky - and sought to correct for it by repeatedly pointing the nose of the aircraft down.
A feature in previous 737 models that allowed pilots to manually override an "electric trimming" process - which automatically budges the nose downward to prevent a stall, does not work in Boeing's 737 MAX 8 planes, Boeing explained in a November 7 bulletin.
That same week, the Federal Aviation Administration issued an emergency notice to all airlines that fly the 737 Max, warning them that erroneous sensor inputs "could cause the flight crew to have difficulty controlling the airplane," leading to "possible impact with terrain."
The deviation likely was caused by what's called a "runaway stabiliser." Stabilisers are, essentially, those small wings on either side at the tail end of the plane. They each have flaps - called elevators - that help to control the elevation the plane.
In case of a runaway stabiliser, pilots are instructed in the cockpit check list to hold the control column firmly, disengaging the autopilot that, in this case, contained the MCAS program. Next, they are told, disengage the auto throttle and manually fly the plane.
"This corner of the performance charts is called the 'coffin corner'," said Mary Schiavo, an aviation lawyer and former inspector general of the U.S. Transportation Department, "and good pilot training teaches you how to get out of coffin corner, but did these pilots realise the plane itself was putting them in coffin corner? Apparently not."
As the pilots struggle to raise the plane's nose, the co-pilot, the committee report said, asked an air traffic controller to "confirm the altitude of the aircraft and later also asked the speed as shown on the controller radar display."
It is not clear if the pilots attempted the runaway stabiliser procedure.
Unions representing pilots at Southwest and American airlines said they were not properly informed about the new system during training.
"We did not know this was on the MAX models," Southwest Airlines Pilots Association president John Weaks told The Washington Post in a November 13 interview, referring to a new automated flight control feature.
The prospect that a runaway autopilot system could have contributed to the crash has already been the subject of at least one lawsuit implicating Boeing, with the father of a Lion Air Flight 610 crash victim filing suit recently.
Soerjanto Tjahjono, who heads Indonesia's National Transportation Safety Committee, said last week that the plane's black box showed "the technical problem was the airspeed, or the speed of the plane." (The plane's cockpit voice recorder has not been recovered.)
"There were four flights that experienced problems with the airspeed indicator," Tjahjono said. The "angle of attack" sensor contributes to the airspeed readings.
In testimony before the Indonesian Parliament last week, Utomo the investigator, said that the anti-stall system had activated on the plane as it flew into Jakarta the night before the crash, but the pilots managed to shut it off.
At the news conference Wednesday, Utomo said that the plane, in both the doomed flight and the previous flight from Bali to Jakarta, had experienced a stick shaker - "a warning that showed that the plane was going to stall," he said.
The committee report said differing data between the sensors appeared rectified by cleaning an electrical plug the night before the crash, and a "test on the ground found the problem had been solved."
But it had not, the report concludes, because when the plane took off shortly after 6 a.m. the following morning, the two flight speed sensors did not agree on the aircraft's speed.
The Indonesian National Police ended their identification process last week, having identified 125 bodies culled from over 666 samples. On Nov. 6, family members strewed flowers into the Java Sea, where the twin-engine jet had nose-dived into, in commemoration. According to the official Ministry of Transportation's regulation, Lion Air is tasked to pay a total of $89,000 to the families of each fallen passenger.
The 737 Max is the most popular plane in Boeing history, with 453 delivered so far and 4,671 on order. It is flown or is on order by close to 40 airlines, with Lion Air in the process of receiving more than 200 of jets.
Boeing said Tuesday that it "continues to work closely with the U.S. National Transportation Safety Board as technical advisers to support the ongoing investigation" by the Indonesian authorities.
The flights of Indonesia's airlines to U.S. destinations were banned in the decade before 2016 because their safety record was considered abysmal by U.S. standards. The crash of the Lion Air flight was the worst in Indonesia since 1997, when 234 people died on the national airline, Garuda, in Northern Sumatra.
EasyJet, Volotea, and Vueling were also fined for similar 'abusive practices'.