Pilots flying blind on Boeing 737 Max crash risks


Two US pilots' unions say the potential risks of a safety feature on Boeing's 737 Max aircraft that has been linked to a deadly crash in Indonesia were not sufficiently spelled out in their manuals or training.

"We don't like that we weren't notified," says Jon Weaks, president of the Southwest Airlines Pilots Association. Dennis Tajer, a 737 captain and spokesman for the Allied Pilots Association at American Airlines Group, says union members are also concerned.

The complaints from pilot union leaders at Southwest Airlines and American are significant because of the size of those carriers' 737 fleets and their Max purchases.

Southwest is the largest operator of the 737 Max and has the most on order with 257 of the jets yet to be delivered. American, the world's largest airline, has outstanding orders for 85 of the planes.

A bulletin from APA to American's pilots said details about the system were not included in the documentation about the plane. "This is the first description you, as 737 pilots, have seen," it said.

Boeing says it is confident in the safety of the 737 Max family of jets.

Few details have been released about the underlying causes of the Lion Air crash on October 29 in the sea near Jakarta, Indonesia, but Indonesian investigators say that an erroneous sensor prompted the plane's computers to push the aircraft into a steep dive.

A long-standing procedure taught to pilots could have halted the dive, according to the regulator and the manufacturer. The Federal Aviation Administration ordered airlines to add an explanation into flight manuals.

When Boeing designed its latest version of the 737, it added the new safety feature to combat a loss of lift, which is a leading contributor to the loss-of-control accidents that by far cause the most crash deaths around the world.

Known as the Maneuvering Characteristics Augmentation System, it was added "to compensate for some unique aircraft handling characteristics," according to a bulletin sent by Southwest's flight operations division to its pilots on November 10.

When the system senses the plane is close to losing lift on the wings, it automatically commands a lowering of the nose to counteract the risk. However, the chief sensor used to predict a loss of lift - known as an angle-of-attack vane - was malfunctioning on the Lion Air flight. It essentially tricked the system into ordering a sharp dive.

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