By Andrew Tangel and Andy Pasztor 

Boeing Co. is making a significant software change to a flight-control system in the new 737 MAX aircraft implicated in last year's Lion Air crash, a fix that comes amid growing world-wide unease about the aircraft's safety following a second crash of the model.

The change, which was in the works before the Ethiopian Airlines plane crash over the weekend, would mark a major shift from how Boeing originally designed a stall-prevention feature in the 737 MAX when it first delivered to airlines in 2017.

U.S. aviation regulators are expected to mandate the change by the end of April.

Boeing publicly released details about the planned 737 MAX software update on its website late Monday. A company spokesman confirmed the update would include a change to use multiple data feeds in MAX's stall-prevention system -- instead of the current reliance on a single sensor.

The change was prompted by preliminary results from the Indonesian crash investigation indicating that erroneous data from a single sensor, which measures the angle of the plane's nose, caused the stall-prevention system to misfire. The series of events put the aircraft into a dangerous dive.

Focus on the update has taken on greater urgency as aviation regulators and airlines around the world have grounded their MAX fleets, following The Ethiopian crash over the weekend -- despite no links being made between the two crashes by investigators.

The MAX software change is expected to take about an hour for each plane, a Boeing spokesman said Tuesday. He declined to offer other details about how the system would weigh the multiple data inputs.

"For the past several months and in the aftermath of Lion Air Flight 610, Boeing has been developing a flight control software enhancement for the 737 MAX, designed to make an already safe aircraft even safer," Boeing said late Monday in a statement.

The FAA has decided to allow the 737 MAX to continue flying, a break with counterparts in countries including the U.K., Australia and Singapore, which grounded the model in recent days.

The investigation into the Oct. 29 Lion Air crash is continuing, but has focused on the stall-prevention system, apparent maintenance lapses and potential pilot error. Investigators have revealed little about the circumstances leading up to the Ethiopian crash, but have found cockpit voice and data recorders.

Boeing had initially designed the system to rely on data from a single sensor that measures what is technically known as the angle-of-attack. Engineers determined such a design would be simpler and was in line with the plane maker's long-held philosophy to keep pilots at the center of cockpit control, a person familiar with the matter said.

Boeing's earlier design of the flight-control system, known as MCAS, has puzzled some pilots and safety experts, who wondered why the system didn't rely on multiple angle-of-attack values.

Mike Michaelis, chairman of the safety committee at American Airlines Group Inc.'s pilot union, welcomed news of the coming Boeing software fix.

"That's the way it should have been in the first place," he said.

Write to Andrew Tangel at Andrew.Tangel@wsj.com and Andy Pasztor at andy.pasztor@wsj.com

 

(END) Dow Jones Newswires

March 12, 2019 14:41 ET (18:41 GMT)

Copyright (c) 2019 Dow Jones & Company, Inc.
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