LAST WEEK, Boeing sent a formal safety directive to all operators of the 737 MAX series, warning that the popular new twin-jet could enter an uncommanded dive. The directive follows the October 29th crash of Lion Air flight JT610, in which 189 people were killed when the plane plummeted into the ocean shortly after takeoff from Jakarta, Indonesia.
Radar data shows the airplane plummeting into the sea at several thousand feet per minute. An immaculate, ultra-modern aircraft, calm weather, an experienced crew… what on earth went wrong?
The problem, Boeing says, occurs when faulty data is generated by the plane’s angle of attack indicator. The indicator is a small, wedge-shaped sensor near the plane’s nose that helps warn pilots of an encroaching aerodynamic stall — i.e., a dangerous loss of lift that results from flying too slowly or too steeply. The faulty data triggers the plane’s stabilizer trim — stabilizers are the wing-like horizontal surfaces beneath the tail — to force the nose down.
This nose-down command can last upwards of ten seconds, Boeing says, and can repeat at five-second intervals, whether in manual flight or with the autopilot engaged. If and when this happens, the stabilizer trim itself gives no indication that it’s moving. All the crew knows is that the plane is nosing over.
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The good news is that whether its movement is commanded by the pilots or uncommanded through a technical glitch like this one, stabilizer movement can easily be shut off through a cockpit switch. The Boeing directive tells pilots exactly how to disconnect the system and prevent a descent. (And you can take additional comfort…