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The US Federal Aviation Administration has issued an Emergency Airworthiness Directive on how to deal with erroneous data from a sensor that, according to investigators, was malfunctioning on a new Boeing aircraft that sank to the sea in Indonesia, killing the 189 people on board.
The directive gives a regulatory weight to a safety bulletin sent by Boeing to operators of its 737 MAX 8 and MAX 9 aircraft on the basis of the findings of the ongoing Indonesian investigation into the crash of a Lion Air plane on 29 October. FAA guidelines are generally followed by other international aviation regulators.
Bad sensor data
The FAA has stated that erroneous data from the angle sensor of attack, preventing the aircraft from stalling and diving, could hinder flight crews from controlling the aircraft and leading to "An excessive dive plate, a significant loss of altitude and possibly impact with the terrain. "
The directive requires airlines to make specific changes to the flight manual procedures to address the problem. Boeing's newsletter indicated that it was directing flight crews to the guidelines in effect.
Indonesian investigators said on Wednesday that the sensor had been replaced on the Lion Air plane the day before its fatal flight, which could have compounded other problems with the plane.
New 737 MAX 8
The Boeing 737 MAX 8, 2 months old, crashed into the Java Sea 13 minutes after takeoff from Jakarta. This flight and its flight of 28 October between Bali and Jakarta had an irregular speed and altitude shortly after takeoff.
The Indonesian National Committee for Transport Safety announced earlier this week that the aircraft had a defective speedometer in its last four flights, based on an analysis of the flight data recorder. President Soerjanto Tjahjono said that the speedometer and sensor problems are related.
Lion Air's first two attempts to solve the airspeed problem did not work and, for the penultimate flight of the aircraft, the "angle-of-attack" sensors were replaced, Tjahjono said. .
On this 28 October flight between Bali and Jakarta, the pilot's and co-pilot's sensors diverged by about 20 degrees. The plane suddenly plunged a few minutes after take-off, which the pilots were able to recover from. They decided to continue their flight to Jakarta at a lower altitude than normal.
During the fatal flight, the aircraft touched the water at very high speed after the flight crew was allowed to return to the airport several minutes after takeoff.
"The fact is that after the replacement of the AOA (sensor), the problem is not solved but it can even increase. Is it fatal? NTSC wants to explore that, "said Tjahjono.
Aviation safety experts said that pilots are trained to safely handle a plane if these critical sensors fail and backup systems are in place.
Audio signals and physical warnings can alert the pilot in the event of equipment malfunction or other hazards, said Todd Curtis, director of the Airsafe.com Foundation.
