Boeing steps up airline outreach on 737 Max after Lion Air crash

Chicago

BOEING Co is trying to assuage 737 Max customers concerned about a little-known anti-stall feature that has emerged as a focus of investigators probing a crash in Indonesia last month that killed 189 people.

Southwest Airlines, the largest 737 Max operator, American Airlines and United Airlines are among the carriers globally pressing Boeing for details of the formerly obscure system, representatives of the airlines say. The aircraft manufacturer first disclosed the possible link to the Lion Air crash on Nov 7 and has been working with the US Federal Aviation Administration to figure out the appropriate remedies, from updating software to improving pilot training.

But as more becomes known about the feature, some US pilots flying the Boeing 737 Max seem increasingly confident that they are suitably trained to disable the automated trim system. Even so, leaders of the three US pilots unions continue to pressure the Chicago-based manufacturer and US regulators for more details about its design - and why it was omitted from pilots' flight operating manuals.

Before the Oct 29 crash near Jakarta, Boeing hadn't widely disclosed that the so-called Maneuvering Characteristics Augmentation System (MCAS) would, in limited circumstances, lower the jet's nose without any input from pilots. The company in recent days has provided assurances that other crucial changes to the upgraded 737 weren't similarly overshadowed.

A day after the largest US pilot union, the Air Line Pilots Association, warned regulators of a "potential, significant aviation system safety deficiency", the United Airlines chapter took a more pragmatic view.

United pilots are already trained on how to disable the anti-stall feature Boeing built into the new 737 Max, according to a report on Friday from Bob Sisk, a United Boeing 767 captain and chairman of the Central Air Safety Committee. "Despite the omission of the MCAS description in the initial 737 Max differences training, United pilots are properly trained in handling an MCAS malfunction," Mr Sisk wrote. "As explained in the new bulletin, when working properly, the system helps us avoid stalls."

If the system responds erroneously, pilots are drilled to shut it off and continue flying the airplane, he added.

The MCAS safety system is designed to automatically push down the nose of the plane if it is in danger of losing lift on the wings, a condition known as an aerodynamic stall. It was added to the 737 Max because flight tests showed the aircraft was more prone to stalls in some conditions than previous models.

If a gauge known as an angle-of-attack vane shows the aircraft is pointed too high relative to the oncoming air, a flight computer automatically pushes down the nose. The MCAS system only works while pilots are manually flying the plane.

In the case of the Lion Air episode, erroneous angle-of-attack gauge signals essentially tricked the plane into thinking it was in danger and commanding a dive, according to Indonesia's National Transportation Safety Committee.

There is an existing emergency procedure requiring pilots to flip two switches that can halt the MCAS commands. However, Boeing didn't specifically notify airlines and pilots that the new system existed or provide guidance on how to handle a malfunction. BLOOMBERG