Originally Posted by
Bend alot
There was the Boeing spokesman that said the AoA disagree only worked above 400ft after they found it actually was not active all all.
So if that is true, then how can the MCAS part of the STS be tested before flight? Lion Air seems faulty AoA fitted - would the annunciation illuminate in this case?
The current MCAS AoA had no limit of disagree, and there was no problem withe the STS operation previously - MCAS really looks more than just a sub-sytem of STS.
Now the that is worrying - variable amounts of input! So if you are going slow with a high angle of attack - how long do you watch that trim wheel spin for?
From the previous thread Mr Driver your instinct would be to trim have you then disabled MCAS and stopped it from its certification requirement?
Would your current practice still stand? - keep flap out, or Autopilot on to bypass MCAS from being able to activate?
In this operator's opinion, certainly not shared by all, the "AOA Disagree" alert that has captured so much attention is not that bid of a deal. If the AOA's are really that far apart, there will be sufficient other indications because of how the AOA information is integrated into other aircraft systems. In the case of both Lion Air flights and ET302, an active stick shaker while the aircraft is accelerating and climbing normally is the big, annoying, and very obvious indication that something is amiss with your AOA system - and that becomes active as soon as the aircraft lifts off the ground.
I'm not sure about what you mean about testing STS/MCAS before flight. There are various logic tests going on in the background for many of our onboard systems, and we will get warning annunciators if one of those self-tests fails. Otherwise, most of our systems are assumed to be working until proven otherwise.
I don't see what is worrying about variable amounts of input. If the system is working and you really are approaching a stall, then that is what you want. If the system somehow got past the new software checks, then MCAS would be making an input when there was no stall while the pilot was hand-flying. As discussed in other threads, the pilot should notice such an anomalous input and take corrective action. At some point, you have to assume that someone is minding the store. If not, there are other systems on the plane that you should be far more worried about.
To your question of what I would do with an unwanted MCAS input, it would be the exact same thing I would do with any unwanted stab trim input. By my count, there are six different sources of input into the electrically-driven trim system on the MAX (five on the 737NG). Our runaway stab procedures are completely agnostic to the source of the undesired trim. Step 2 of that procedure is to oppose and counter the unwanted trim with the yoke trim switch. It is not until Step 5 that the cutout switches are used. This was one of the errors the ET302 crew made - they went right to Step 5. Once MCAS is disabled, yes, the aircraft no longer meets its certification dispatch requirement. That statement also applies when we lose engines, hydraulic systems, generators, and so forth. That is why we have non-normal procedures to get the aircraft back on the ground where it can be fixed.
The technique I spoke of before about engaging the autopilot before flap retraction was an interim approach until Boeing rolled out a long term fix. That will no longer be necessary with the new software.