Originally Posted by
Just the fax maam
In the absence of conclusive evidence that demonstrates with absolute certainty that the main electric trim system was 100% operative throughout all phases of both fatal accidents [for the record, there is none], investigators are left drawing probable conclusions based on the available evidence:
1> It is not very plausible that two separate crews comprised four trained, experienced, pilots all elected not to attempt to trim ANU (more than a sub-second blip) when presented with life-threatening ongoing opposing trim in clear conditions in sight of the ground, whilst simultaneously commanding nose up at forces likely not previously experienced.
2> The "blips" are present in the last seconds of both fatal accidents.
3> The "blips" are consistent with an initial ANU trim command, but each has no resulting actual ANU trim of any significance whatsoever, certainly nothing like that required to improve the situation they were presented with. See 1> above.
4> The "blips" are entirely consistent with a shorted and/or overpowered motor.
5> The "blips" look exactly as we would expect a command to an overpowered motor to record; a power spike then null.
6> The manual trim was also overpowered under the aerodynamic loads experienced at that time.
7> "Trim with me" is not the announcement one would expect to be made by a PF who's trim is functioning correctly.
8> The actions of the MS crew, including attempting to briefly trim AND in such a situation, are consistent with a crew dealing with an inoperable main electric trim in the ANU moment.
9> Both crews were aware that an 'auto' trim was trimming against them but were ultimately unable to prevent their aircraft from trimming them into the ground to their certain death and the demise of all onboard.
10> XAA's all around the world have grounded all aircraft of this type until further notice.
Concerns about the main electric trim system was absolutely a valid line of enquiry when the MAX accidents first occurred. However, after much scrutiny, this has turned into a dry hole. There really isn't anything there.
First, as to the anomalies you point to, we could get out our magnifying glasses and try to discern what was happening in the final moments of these flight, but that really isn't necessary. We can dispense with all the "blip" data you point to because they all occurred at speeds in excess of Vmo. From a certification standpoint, nothing is guaranteed outside the certification envelope, so no corrective action is warranted. Within the flight envelope, on the other hand, ever time we see evidence that the yoke trim switch was depressed, the stab moved as expected. Every time the yoke trim switch was used while MCAS was attempting to trim, the MCAS input stopped - just as designed.
Second, it seems that you are trying very hard to read into the data something that isn't there. I know it is hard to contemplate that the flying pilots (Lion Air First Officer, Ethiopian Captain) were not effectively use the main electric trim, but that really is the most straightforward answer to the data. That is a training issue, not a design issue.
Finally, and probably most significantly, it is important to note that the 737MAX and its related systems have been under a great deal of scrutiny for many months now. People and organizations with significantly greater knowledge and resources than us have been pouring over everything about the design, certification, training, and operations of this aircraft. There are two investigative bodies (Ethiopian and Indonesian) who are very motivated to find any exculpatory evidence that removes the crew as a factor in these accidents. There have been numerous informative investigative reports by outlets such as the Seattle Times, Wall Street Journal, Washington Times, and Aviation Week & Space Technology to name just a few. Every major certificating authority in the world is looking at this aircraft. Through all this, we have learned many, many things that shed light on problems with the MCAS design, the certification process, the simulators, and crew training. These authorities have publicly laid out their concerns about the type of things they would like to see addressed before the MAX is allowed to fly again.
Conspicuously absent from any of these discussions is any call by any authority for a redesign of the main electric trim system. I have heard of no one in a position of authority suggesting a problem with or a need to redesign any switches, relays, linkages, or motors related to the main electric trim system. If I missed something along these lines, please point me to the reference. If this were a Sherlock Holmes mystery, we could call this a case of the dog that did not bark. The dog isn't barking because there is nothing there.
There certainly are issues with the MAX that need to be dealt with. The main electric trim does not appear to be one of them.