During 11 minutes of a 13-minute flight, the pilots of Lion Air Flight 610 fought 26 times to level off their airplane, but the Boeing anti-stall system repeatedly pushed the nose down, eventually winning the battle and plunging the plane into the sea, killing 189 passengers and crew.
Indonesia’s National Transportation Safety Committee (KNKT) issued a preliminary report (PDF) this week about the October 29 crash, saying that the Boeing 737 MAX was not air worthy, causing an eight-minute fight between the crew and the computer, as the pilots worked desperately to keep the plane in the air and the automated systems were determined to plunge it into the ocean.
The findings appear to confirm concerns that the plane’s Angle of Attack (AOA) sensors malfunctioned, wrongly telling the automated systems that the plane was in a stall because the nose was too high.
A day earlier, the same plane landed successfully, despite similar problems. Engineers told the pilot in charge that they had replaced the AOA sensor and tested it. The pilot believed the problem was resolved. However, in flight, problems occurred yet again.
In fact, the report found that the Aircraft Flight Maintenance Log recorded several problems linked to airspeed and altitude indicators since October 26.
Lion Air Flight 610 crashed after departing from Jakarta, Indonesia airport on October 29, with 189 passengers and crew. The plane was destined for Pangkal Pinang, but crashed into the Java Sea approximately 13 minutes into the flight, around 6:30 a.m.
While no official cause has been attributed to the accident by Boeing or federal investigators in the U.S., on November 7, the Federal Aviation Administration (FAA) issued an emergency air worthiness directive which advised all pilots operating a Boeing Model 737 Max that the AOA sensors may produce erroneous readings and cause the plane to abruptly dive, increasing the risk of a crash.
According to the FAA, the planes are equipped with an AOA which measures the angular difference between the direction the aircraft is moving and the pitch of the aircraft’s wing. Boeing has discovered the system can produce inaccurate measurements telling pilots the nose of the plane is too high in relation to the current of air. As a result, pilots may continue to pitch the nose downward or the automatic system may forcibly pitch the nose down.
Boeing faces a growing number of wrongful death lawsuits from relatives of passengers who died on the flight, each claiming that defective sensors caused the crash.
The lawsuits indicate that before the directive, which came as a result of the ongoing investigation into the crash, pilots were not warned about the risk of problems with the AOA sensor.