XRAYretired wrote:planecane wrote:flyingphil wrote:Regulators knew before crashes that 737 MAX trim control was confusing in some conditions: document
https://www.reuters.com/article/us-ethi ... SKCN1RA0DP
U.S. and European regulators knew at least two years before a Lion Air crash that the usual method for controlling the Boeing 737 MAX's nose angle might not work in conditions similar to those in two recent disasters, a document shows.
I have not seen this before.. sorry if it has been posted before, not easy to keep up with the MAX news.
Doesn't look good for Boeing or the FAA.
Q4 is almost upon us and Boeing has not submitted the fix to the FAA and the MAX10 has yet to fly..
What isn't made clear by the article (which is probably the result of the news media rushing to get the "scoop" without first getting all the facts) is WHY the electric trim wouldn't work in certain conditions. The article says:It specifically noted that at speeds greater than 230 knots (265mph, 425kph) with flaps retracted, pilots might have to use the wheel in the cockpit’s center console rather than an electric thumb switch on the control yoke.
Based upon the conditions, it appears that the reason is somehow related to the MCAS software. But, from what we know, trimming opposite to MCAS would have interrupted it temporarily. It doesn't make sense that the same motor that drives the stabilizer movement just fine on the NG under these conditions would reach some kind of physical limit on the MAX. It's the same stabilizer so the aerodynamic forces should be roughly equivalent under the same conditions. Does this mean that a software limit was added to MCAS to not allow the pilot to electrically trim out all of the MCAS input? IF that is the case, then the runaway stabilizer NNC as written would not work once the MCAS runaway progressed beyond a certain point.
I guess for clarification we either need more detailed leaks or will have to wait for the final report on the Lion Air crash.
Again if you read the EASA finding from the original certification. This sentence may provide the clue:
Boeing set the thumb switch limits in order to increase the level of safety for out-of-trim dive characteristics(CS 25.255(a)(1)). The resulting thumb switch limits require an alternative trim method to meet CS 25.161trim requirements in certain corners of the operational envelope.'
It may indeed indicate another 'minor' change to flight controls that was not disclosed.
I missed this back in March when it was originally published. I just read the EASA document, and then I went back and looked at my MAX differences material. We were simply told "the trim authority for main electric and autopilot trim is less than for manual trim". For flight crew, this is a much bigger deal than MCAS, and I'm extremely disappointed that Boeing and the FAA didn't feel we needed to know the specifics.
Once I have my coffee, if everyone is ready to grab the pitch forks, fire up the torches and head over to Boeing and the FAA I'm in.