The FAA has issued an emergency directive to anyone flying the Boeing 737 MAX, the type of plane that crashed in the Lion Air Flight JH 610 incident, related to the faulty sensors that reportedly fed bad information to the pilots. Meanwhile, investigators have reported that the plane received a replacement angle-of-attack sensor (a system that measures whether the plane's nose is too high relative to the current of air) the day before the deadly crash.
As Bloomberg reported earlier this week, Boeing issued a bulletin to 737 MAX operators warning them that faulty inputs from airflow sensors could have contributed to the Lion Air crash. The Boeing statement gave few details, saying that “the investigation is ongoing.” The FAA's directive backs up that bulletin by giving anyone who flies the 737 MAX three days, starting Wednesday, to revise their airplane flight manual for that model.
The FAA said it was taking the action to “address possible erroneous angle of attack inputs” that could put the plane in a sudden dive. The FAA said airline operators need to revise the manual “to give crew Horizontal stabilizer trim procedures to follow under certain conditions." In the U.S., the order affects American, Southwest, and United, which together operate 45 MAX jets.
Here's the official statement:
“Boeing has released a Flight Crew Operations Manual Bulletin regarding the potential for erroneous angle of attack input on 737 Max aircraft. The FAA plans to mandate the Flight Crew Operations Manual Bulletin by issuing an Airworthiness Directive (AD). 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. The FAA has alerted affected domestic carriers and foreign airworthiness authorities who oversee air carriers that use the 737 MAX of the agency’s forthcoming action."
The new revelation—that the doomed 737 received a new sensor after a flight on October 28, the day before the deadly crash—adds to the growing evidence of a serious problem with the sensors and flight data being fed to the crew of Lion Air 610. Data downloaded from the flight data recorder, which was recovered by divers searching the underwater crash site, have revealed a series of glitches in three flights prior to the crash that gave flawed airspeed and other information to the cockpit.
If AOA sensors fail, it can cause the plane’s computers to incorrectly show the plane is heading into an aerodynamic stall—which, in turn, can put the jet into a sudden dive to restore airspeed.
“It’s too early to tell if the sensors caused the accident,” said John Goglia, an aviation safety expert and former member of the National Transportation Safety Board. He said that sensor equipment has become more automated with each new generation of aircraft, and that, in turn, introduces a new risk.
“This could be a training issue,” he said. “The automation keeps marching forward and this is most advanced model that Boeing has built.” It’s still unclear whether the issue is one of an actual flaw, or a procedure that wasn’t correctly followed.