PPRuNe Forums - View Single Post - MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures
Old 24th Sep 2019, 14:48
  #2585 (permalink)  
Fly Aiprt
Join Date: Mar 2019
Location: French Alps
Posts: 326
Originally Posted by PEI_3721 View Post

The optional display of AoA value may have be an operational requirement, thus AoA Disagree required. AoA information is already within the EFIS speed display of low speed awareness.

A major weakness of a stand alone AoA display is that with dual system sensors, if one malfunctions it is impossible to identify which of the two is correct (the MCAS saga), additionally many other systems can be ’confused’; irrespective of the disagree alert.
Both EFIS displays should be removed with a disagreement to prevent incorrect interpretation.

That's why I drew the AOA indication with a big red bar on it , showing it is no longer available or reliable.
It seems general aviation EFIS industry is ahead on this matter.

Originally Posted by PEI_3721 View Post
Re ‘MCAS active’ - red indication. This display would be unacceptable for certification as it violates the requirement to only use ‘red’ level alerting for failures requiring urgent attention or action (see trim below). The alert also violates recommended principle of not to annunciate normal operation of background systems, e.g. STS.
Alerting for MCAS unavailability could be required if it’s absence affects flight handling.
Agreed. I drew it in red because some times ago, MCAS activation was synonymous with "this aircraft is trying to kill you".
Any color would do.
As to not annunciate normal operation etc., disagree.
When STS operates, wheels do turn, clicks and white bars have been provided to make the crew aware of the activation.
Most every variation on the theme of "the crew should have identified" relies on this signal of activation.
Except that having something clearly in the field of vision is far more ergonomic.
Same for the MCAS, which should show when it activates, if only to signal some corner of the flight/AOA envelope is being entered.
Just like the bars for low speed on the speed ribbon.

One must not reason in terms of "we've always done it that way".
Obviously things are to be changed in ergonomics and training.
Presenting AOA indication at a useful place is viewed as an improvement. If pilots disagree, they are free to not include it in their scan. Or ask for more and better training ;-)
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