Boeing 737 Max safety alert issued after Lion Air crash

Inspectors found faults on two other Boeing 737 MAX jets, including one which mirrored a problem reported on board the Lion Air plane.

This measures at what angle an aircraft is flying and air is passing over the wings.

The news agency noted that angle-of-attack errors can cause pilots to lose control of an aircraft and make it impossible to correct the course of a flight, and this was particularly an issue when jet aircraft were first entering circulation.

The latest information released by investigators still doesn't answer why the pilots on three previous flights were able to handle the problem while the crew on October 29 ended up diving at high speed into the sea, said John Cox, president of consulting company Safety Operating Systems and a former airline pilot. Erroneous readings from the AOA sensor could push the plane into an aggressive, unwarranted dive.

Frozen pitot tubes were blamed for the 2009 crash of Air France Flight 447, which killed all 228 people on board.

Cox said that once investigators have all the data, they will work backward to determine if there was a problem with one of the plane's systems or if pilot decisions put the plane in peril.

"We will ... conduct a special audit of the crews' qualifications and staff communication", transportation minister Budi Karya Sumadi told reporters Monday as he announced the probe into Lion's operations. That failure caused the aircraft's systems to think the airplane was in danger of stalling, causing the computer to steadily adjust the trim tabs on the horizontal stabilizer to nose the aircraft downward, thereby picking up speed.

Boeing will caution its customers of "erroneous readings" from a flight-monitoring system can cause the planes to abruptly dive, Bloomberg quoted an anonymous source as saying.

"There are some things that we ask for explanation and some that we ask to be removed, and there has been an agreement between NTSC and Boeing to release a new procedure to all Boeing 737 MAX users in the world".

The problem with the planes is in the "angle of attack" sensor which calculates the position of the plane relative to the air current. When one of these faulty readings occurs, the plane may incorrectly sense it's in an aerodynamic stall.

The Boeing 737 MAX is a more fuel-efficient version of the manufacturer's popular single-aisle jet.

Under the subject heading, the Boeing bulletin says: "Uncommanded Nose Down Stabilizer Trim Due to Erroneous Angle of Attack (AOA) During Manual Flight Only".

Earlier this week, investigators said the plane's flight data recorder showed that an airspeed indicator malfunctioned during last week's fatal flight as well as three previous flights.

After an engine on a Southwest Airlines plane fractured earlier this year over Pennsylvania, killing a passenger, CFM International issued multiple bulletins to operators of its CFM56-7B power plants. In addition, a system known as pitch trim can be changed to prompt nose-up or nose-down movement.

"When there was a problem, the pilot would write it down and the mechanic would do (a repair).Then the plane would be declared airworthy".

The angle of attack is incredibly important.

Alan Diehl, a pilot and safety consultant, said the report that the same problem happened four times and was never fixed suggests that the problem may have been intermittent, making it harder to pin down.

  • Rogelio Becker