In the over 1,600-page flight manual of Boeing's 737 Max 8 planes, the aircraft's new MCAS computer system, now at the centre of the investigations into two deadly crashes, is mentioned only once by name — in the glossary of abbreviated terms.
That brief mention in the manual, a copy of which was obtained by CBC News, has prompted some speculation that more details about the anti-stall computer system may have been included in previous drafts, but then left out of the final version.
"I think the fairly obvious conclusion is that a broader explanation of MCAS was included in an earlier edition of the manual, and somewhere along the way it ended up on the cutting room floor," said Judson Rollins, a New Zealand-based aviation consultant, who worked for three airlines and a plane manufacturer.
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Rollins believes it was cut "to prevent the MCAS from having to be included in 737 Max transition training, which in turn will save 737 Max operators training costs."
Few hours training
But Rollins said that including MCAS in the manual would suggest it was a significant enough system that pilots would need to undergo classroom- or simulator-based training.
Costs for that extended training, he said, could range anywhere from hundreds of thousands of dollars per plane to the low millions.
The operating manual mentions the term MCAS under the section entitled "Abbreviations," where the acronym is defined as "Maneuver Characteristics Augmentation System." That's the one and only reference to MCAS, which is suspected of playing a role in two recent crashes involving Max 8 planes in Indonesia and Ethiopia, which killed 346 people in total.
Raymond Hall, a former Air Canada pilot, said "it's very interesting" that the subject of MCAS was broached in the manual, but that "no follow-up" was done to explain it. Hall said that Boeing has historically been quite vigilant in making sure that all of its systems are laid out in clear terms, both in pilot training and in pilot manuals.
"The system is critical to the safety of the flight. And pilots ought to have known that it was there, ought to have been able to recognize it when it was implemented and ought to have been able to respond effectively," Hall said.
'Critical to the safety of the flight'
He said he didn't think there was any "sinister action" on the part of either Boeing or the U.S. Federal Aviation Administration (FAA), but that it was a "matter of oversight shortage."
The Seattle Times recently reported that the FBI was joining a federal grand jury criminal investigation into the certification process that approved the safety of the 737 Max.
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The crash of Ethiopian Flight 302 on March 10 and that of a Lion Air plane in Indonesia in October — both of them Boeing 737 Max 8 jetliners — has prompted Canada, the U.K. and other countries to ground the aircraft. According to investigators, data obtained from the flight data recorder in the Ethiopian crash reveal "clear similarities" with the Lion Air plane disaster.
Following the Lion Air crash, pilots sat down with Boeing executives to complain they had not been given any information about the new MCAS system.
Dennis Tajer, an American Airlines pilot and spokesman for the Allied Pilots Association, told the Washington Post that during that meeting, executives said they didn't inform pilots about the MCAS because they didn't want to "inundate" them with too much information.
In an emailed response to CBC News, Boeing did not deny that there were no references to MCAS in the manual. But spokesman Paul Bergman said that the relevant functions of the system were "described" in the manual, and that "media reports that we intentionally withheld information about airplane functionality from our customers are simply untrue."
Yet days after the Lion Air crash, Boeing issued a safety bulletin, providing for the first time details on how the anti-stall system worked and how to shut it down in case it malfunctioned.
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The Max, which came into service two years ago, features the new automated MCAS, which is meant to prevent an aerodynamic stall, which can cause a loss of lift, sending the plane downwards in an uncontrolled way.
This system is designed to force the plane to pitch down if it thinks the aircraft is about to stall. Reports suggest that in the Lion Air crash, the MCAS may have responded to a faulty sensor, leading it to think the plane was stalling, and causing the plane to lurch downwards. The pilots, unfamiliar with the MCAS system, may have been helpless to respond and unable to bring its nose back up.
The New York Times reported that in the final minutes of the Lion Air flight, the pilot handed the controls to his co-pilot and flipped through the pages of a technical manual, trying to figure out what was happening.
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With files from Reuters, The Associated Press