The previously undisclosed detail on the earlier Lion Air flight represents a new clue in the mystery of how some 737 Max pilots faced with the malfunction have been able to avert disaster while the others lost control of their planes and crashed.
Investigators suspect that incorrect sensor readings feeding into a new automated flight-control system may have played a role in the Indonesian crash, and the Ethiopian plane had a similar, erratic flight path.
The next day, under command of a different crew facing what investigators said was an identical malfunction, the jetliner crashed into the Java Sea killing all 189 aboard.
The Ethiopian Airlines disaster on 10 March that killed 157 people led to the grounding of Boeing's marquee MAX fleet globally and sparked a high-stakes inquiry for the aviation industry.
The jet then warned pilots incorrectly that it was stalling, and pointed its nose downwards in response.
From July 2013 to March 2016, he served as the vice-president of Safety, Security and Compliance, and oversaw the Commercial Airplanes Organisation Designation Authorisation - a programme that takes on specific safety certification duties on behalf of the US Federal Aviation Administration.
The preliminary report into Lion Air Flight JT610 crash, published by Indonesia's National Transport Safety Committee (KNKT) on November 28, 2018, revolves around data recovered from the Flight Data Recorder (FDR).
Boeing Co declined to comment.
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Some U.S. pilots have complained they were unaware of the new system, which is mentioned in the index of the aircraft's full manual but not the text, according to a version seen by Reuters.
The Ethiopian Airlines crash has shaken the global aviation industry and cast a shadow over the flagship Boeing model meant to be a standard for decades to come, given parallels with the Lion Air calamity off Jakarta in October.
"We have been working very hard to minimize that impact", said Lucie Guillemette, the airline's executive vice president.
Canada's transport ministry, also among the last to ground the plane, has come under fire in the press and from the political opposition for waiting too long.
As the 31-year-old captain tried in vain to find the right procedure in the handbook, the 41-year-old first officer was unable to control the plane, two of the sources said.
The prestige of Ethiopian Airlines, one of Africa's most successful companies, and Boeing, the world's biggest planemaker and a massive USA exporter, is at stake in the inquiry.
MCAS is driven by a single sensor near the nose that measures the so-called angle of attack, or whether air is flowing parallel to the length of the fuselage or at an angle.
In an open letter on the Boeing's website, company CEO Dennis Muilenburg said: "soon we'll release a software update and related pilot training for the 737 MAX that will address concerns discovered in the aftermath of the Lion Air Flight 610 accident".