Indonesian investigators said the pilot and co-pilot aboard the Lion Air jet, which had crashed into the sea last week, used separate indicators that registered very different values for a key parameter during a flight just before his last voyage.
In the meantime, on Tuesday there was a security warning about potentially suspicious flight control software for the crashed version of the aircraft. Boeing provided the pilots with special instructions on how to handle the new 737 Max 8 jets when they encounter confusing or inaccurate information.
Boeing warned that misusing this information could lead to a steep descent of the affected aircraft model. The US aviation regulators said they were ready to comply with their own directive.
The Boeing warning is the first public indication that investigators are considering a potential software error or misinterpretation by pilots in relation to an essential system that measures the "angle of attack" of an aircraft, or how high or how deep the nose of one Plane is. Lion Air Flight 610 crashed into Java Sea last week, killing all 189 on board.
The crash is the first major accident with a Boeing 737 Max 8, the latest variant of the popular 737, which takes a closer look at the new model. The plane was delivered to Lion Air in August, one of Asia's largest low-cost airlines. Boeing is involved in the investigation of the crash.
The Boeing notification is an official warning to pilots that indicates potential hazards from the interaction of certain software with other cockpit alarms.
Boeing has given operators a bulletin on dealing with the problem late Tuesday. The warning ends when a particular on-board system needs to be replaced or inspected. Nor is any final conclusion to be drawn as to whether a system failure has resulted in a fatal accident.
Rather, the announcement is an official warning to pilots to alert them to possible hazards arising from the interaction of certain software with various other cockpit alarms. Boeing reaffirmed the importance of following standard procedures in such circumstances.
The Indonesian investigators announced on Wednesday separately that had occurred on two previous flights of the aircraft problems with the airspeed indicator. Afterwards, the technicians selected a sensor for the angle of attack. The jet's cockpit does not display a pitch measurement, but the readings are stored by the flight data recorder and take into account the airspeed calculation. The airspeed is then forwarded to the pilot and the copilot in separate indicators in the cockpit.
After replacement of the sensor, the jet was released for the penultimate flight. Investigators pointed out information from the jet's reconstructed flight data recorder and said the pilots and copilot inputs differed by 20 degrees during the flight. The problem was identified and corrected by the crew during the flight, which was able to travel to Jakarta and request a priority landing. The pilots manually flew for about an hour and 45 minutes, depending on who is familiar with the matter.
The next day, the plane crashed into the Java Sea on its last high-speed, high-speed flight.
Boeing said on Tuesday that his alert was directed to cases "where a sensor (pitch) fed incorrectly."
During the last flight of the aircraft, the crew returned to manual flight after receiving unreliable flight speed data in good weather shortly after departure from Jakarta, according to preliminary information from the investigation. Minutes after the crew reported the situation to the air traffic controllers and gradually gained altitude as part of an apparent effort to remedy the problem, the twin-engined aircraft crashed at high speed into the water.
– Robert Wall and I contributed Senata contributed to this article.
Write to Ben Otto at email@example.com and Andy Pasztor at firstname.lastname@example.org