BANGKOK • Boeing faced new scrutiny on Tuesday over the crash of one of its planes into the sea off Indonesia last month, as airlines, pilots and regulators sought to determine whether it had underplayed the complexity of a new emergency system suspected of having malfunctioned on the doomed jetliner.
Investigators have been focused on whether the plane, Lion Air Flight 610, crashed because the system, which is designed to pull the plane out of a dangerous stall, activated based on inaccurate data transmitted or processed from sensors on the fuselage.
The plane plunged nose down into the Java Sea, killing all 189 people on board. The precise cause or causes of the crash remain unclear.
Boeing has been selling the model that crashed, the new 737 Max 8, as requiring little additional pilot training for airlines that already use the previous version of the plane. The 737 Max 8 is in a ferocious competitive battle with an update of the Airbus A320, and minimising the costs of upgrading to the new model is one of the keys to winning orders from airlines.
The pilots' union for American Airlines, which also flies the Max 8, said the emergency system in question had not been included by Boeing in the standard operating manual. Also, the flight check list - containing information for manually overriding the emergency system - was incorrect, the union said.
The emergency system is intended to manoeuvre the plane out of a stall, when its nose is often angled too sharply upward. The system automatically pushes the nose down. If activated incorrectly, it could have sent the plane into its fatal dive, especially if the pilots were not properly trained on how to deal with such a situation.
Boeing has delivered 200 of the planes to airlines around the world, with many more in the pipeline. It is already in use in the United States by American Airlines and Southwest, and other customers include Air Canada and Norwegian Air.
Boeing said it is assisting in investigations into the crash, but did not directly address questions on why it did not do more to emphasise the changes in the anti-stall system.
"The investigation into Lion Air flight 610 is ongoing and Boeing continues to cooperate fully and provide technical assistance at the request and under the direction of government authorities investigating the accident," it said.
The US Federal Aviation Administration had received a letter from Boeing requesting permission to update the 737 Max 8's flight manual. This is not unusual after the agency issues airworthiness directives, but it is not known what specific changes Boeing was requesting.
The question of whether cost pressures contributed to any decision by Boeing to fully brief airlines on how the new emergency system works and how pilots need to respond differently to it in case of a malfunction injected a new element into the investigation.
Boeing had told airlines that pilots qualified to fly the earlier version of the plane, the 737NG, would need to do just 16 hours of training on a computer to be ready to fly the new Max version.
American Airlines said it had not had any similar problems with its 16 Max 8 jetliners, but that it had been unaware of the issues with the way the anti-stall system works.
Indonesian transportation officials have said repeatedly the Max 8 manual being used in the country did not contain crucial information about the new anti-stall mechanism. Mr Soerjanto Tjahjono, head of Indonesia's National Transportation Safety Committee, said Boeing's manual did not adequately describe how this new mechanism worked and what to do if it was triggered incorrectly.
Pilots would have only a few seconds to respond to this situation, aviation experts said, especially if a plane was flying at low altitude, as was the case with the Lion Air flight.