Boeing alerts pilots after Indonesian aircraft crash
Boeing has issued a safety bulletin reminding pilots how to handle erroneous data from a key sensor in the wake of last week’s Indonesia plane crash.
The US aircraft maker said investigators probing the Lion Air crash off the coast of Indonesia, in which all 189 on board were killed, found that one of the “angle of attack” sensors on the new Boeing 737 MAX jet provided erroneous data.
Experts say the angle of attack is a crucial parameter that helps the aircraft’s computers understand whether its nose is too high relative to the current of air a phenomenon that can throw the aircraft into an aerodynamic stall and make it fall.
Some modern aircraft have systems designed to correct the posture of the aircraft automatically to keep flying safely.
There are also procedures for pilots to follow in the event of missing data from damaged sensors on the fuselage, but it remains unclear how much time the crew of flight JT610 had to respond at the relatively low altitude of about 3,000m.
An angle of attack sensor was changed by mechanics in Bali the day before the crash, Indonesia’s national transportation safety committee said.
The captain and first officer flying from Bali to Jakarta the night before the crash had indicators displaying differences in angle of 20º, the committee said, but that flight landed safely despite the issues in the air.
Boeing said in a statement that its note to airlines underscores “existing flight crew procedures” designed to address circumstances in which information coming into the cockpit from the sensors is wrong.
The Boeing 737 MAX has three such blade-shaped sensors. Erroneous readings can in some circumstances cause the 737 MAX to point the nose down to keep air under the wings and avoid a stall, according to a person briefed on the matter.
Boeing’s bulletin related only to the 737 MAX, the latest version of the world’s most sold family of aircraft, which has been in service for just more than a year.
The US Federal Aviation Administration (FAA) said it will issue an airworthiness directive to make Boeing’s advice mandatory. “The FAA continues to work closely with Boeing, and as a part of the investigative team on the Indonesia Lion Air accident, will take further appropriate actions depending on the results of the investigation,” it said.
Boeing has delivered 219,737 MAX jets to customers globally, with 4,564 orders for aircraft yet to be delivered.
The Lion Air crash was the first involving the new version, which airlines introduced into service in 2017.
Indonesian authorities have downloaded information from the flight data recorder that shows a cockpit indicator on the Lion Air jet was damaged for its last four flights.
A search for the cockpit voice recorder, the second socalled black box, remains under way.