[SystemSafety] "FAA chief '100% confident' of 737 MAX safety as flights to resume"

Pekka Pihlajasaari pekka at data.co.za
Wed Dec 2 20:13:35 CET 2020


A readable news article published in Leeham News after the Lion Air, but before the Ethiopian Airlines, accident [1] describes the expected behaviour of the control yoke, and how the MAX deviates from this. It explains how the larger and repositioned engine nacelles produce lift that causes the deviation from the established response and drove for the introduction of something (read MCAS) to reduce the need for crew training.

The Final Committee report of the House Committee on Transportation and Infrastructure [2] has on p. 88:
In addition, when piloting the 737 MAX during a test maneuver known as a high speed wind-up turn, which is required for FAA certification and involves flying the plane at a high AOA, the force that pilots felt on the control column was not as smooth as required. As pilots pulled back on the column during the maneuver, they could feel a slackening of resistance. Conversely, the FAA mandates that airplanes handle this maneuver with a smooth transition. To address this, Boeing’s engineers initially considered adding small metal vanes known as vortex generators on the wings. This proposed fix did not prove to be satisfactory to address the issue, however. Ultimately, Boeing decided to add the Maneuvering Characteristics Augmentation System (MCAS) to the 737 MAX to help the aircraft compensate for those flight conditions.

Perhaps these clarify the response of the aircraft in this unusual flight regime and explain why pilots failed to respond appropriately.

Pekka Pihlajasaari
pekka at data.co.za           Data Abstraction (Pty) Ltd         +27 11 484 9664
1.         Boeing’s automatic trim for the 737 MAX was not disclosed to the Pilots - Leeham News and Analysis<https://leehamnews.com/2018/11/14/boeings-automatic-trim-for-the-737-max-was-not-disclosed-to-the-pilots/>
2.         2020.09.15 FINAL 737 MAX Report for Public Release.pdf (house.gov)<https://transportation.house.gov/imo/media/doc/2020.09.15%20FINAL%20737%20MAX%20Report%20for%20Public%20Release.pdf>

From: systemsafety <systemsafety-bounces at lists.techfak.uni-bielefeld.de> On Behalf Of Olwen Morgan
Sent: 02 December 2020 17:56
To: systemsafety at lists.techfak.uni-bielefeld.de
Subject: Re: [SystemSafety] "FAA chief '100% confident' of 737 MAX safety as flights to resume"

On 02/12/2020 14:55, Grazebrook, Alvery wrote:
Hi Olwen,

As Peter pointed out, I don't mean "Pitch", I mean "angle of attack". Sorry, sloppy of me.

On Wed, 2 Dec 2020 at 13:52, Grazebrook, Alvery <alvery.grazebrook at airbus.com<mailto:alvery.grazebrook at airbus.com>> wrote:


Does this help?

Thanks but not really.

I know what the rules say, if only because of PBL's inimitable Germanic insistence on quoting them to me.

My knowledge of aerodynamics and aeronautical engineering could be scraped onto a single sheet of toilet paper (and could be disposed of like other such scrapings).

What I want to know from those with better knowledge is what is happening to the distribution of air pressure over the relevant airframe surfaces in the region where the slope of the stick force curve ceases to be stable according to the JAR rules?

So far, nobody has offered me an answer to that question.


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