When Lion Air Flight 610 crashed, killing 189 people last October, pilots frantically looked through a handbook, searching for a way to override the plane’s automatic aircraft nose down feature, triggered by inaccurate sensor readings. They failed, and according to The New York Times, their window for success was exceedingly small. In Boeing simulations of the crash, the window between when the system engaged and when the plane’s nosedive became irreversible could be as small as 40 seconds.
Boeing ran a series of simulator tests with pilots from several different airlines over the past weekend during which pilots were tasked with overcoming the sensor misreadings that played a part in the ill-fated Lion Air flight, during which the 737 Max’s MCAS safety feature triggered a fatal nosedive, the New York Times reports.
The pilots were tasked with subverting the safety feature as originally designed, and then with a software update provided by the manufacturer. This testing showed that the system, which engages in 10-second bursts with a resting time of five seconds between engagements, could doom a plane if allowed to proceed unabated as few as three times in a row, a 40-second span.
These engagements could be temporarily counteracted by the flip of a thumb switch, but to disable the system entirely, pilots would have to execute a lengthier string of commands all while MCAS would continue to engage, dragging the craft’s nose towards a fatal dive.
From The New York Times:
If the system starts pushing the plane’s nose down, pilots can reverse the movement via a switch at their thumb, a typical reaction in that situation. In doing so, they can potentially extend the 40-second window, giving them more time to avoid a crash.
To fully neutralize the system, pilots would need to flip two more switches. That would shut off the electricity to a motor that allows the system to push the plane toward the ground. Then the pilots would need to crank a wheel to correct whatever problems had emerged. … In the Lion Air crash, pilots used the thumb switch more than two dozen times to try to override the system. The system kept engaging nonetheless, most likely because of bad readings from a sensor, until the plane crashed into the Java Sea, killing all 189 people on board.
Updates to the system mitigate this danger by relying on multiple sensors, limiting the number of times the system can engage, and preventing the system’s corrections from being so extreme that they could not be undone by pilots.
On Sunday, reports indicated that the FAA had tentatively approved a software update for Boeing’s 737 MAX fleet which, for the time being, remains grounded.
Investigators probing the cause of the Lion Air disaster and the crash of Ethiopian Airlines Flight 302 earlier this month have remarked upon the “clear similarities” between each doomed flight, both of which took place on the 737 Max 8.
Source: The New York Times
Originally posted on Popular Mechanics