Originally Posted by
FCeng84
VicMel - I really appreciate your thoughtful response. I sense that overall you and I are on the same page. Please allow me to provide a few inputs on your points:
A i) The update in work by Boeing is in response to the Lion Air accident, not the Ethiopian accident. Hopefully we will know more about the Ethiopian accident soon and only then will it be possible to determine if this same update would have helped lead to a better outcome in Ethiopia.
A ii) It seems that the proposed update will disable MCAS if the two AOA vanes do not track each other sufficiently. The severity of the degradation in handling qualities without MCAS must be minor enough to allow for this reduction in MCAS availability. Boeing must be assuming some probability for an AOA sensor failure and then showing that it is acceptable to turn MCAS off twice as often as a failure of either AOA sensor would lead to MCAS shut down.
A iii) No MCAS when AOA vanes do not track. See A ii above.
A iv) I doubt that we will find that the MCAS update reduces the size of a single increment of MCAS stabilizer motion. I can't imagine that Boeing would have given this function any more authority than absolutely needed to meet FARs and thus there is probably no room to reduce its single increment authority.
C) MCAS is implemented within the FCC within the same software that controls other automatic stabilizer control functions such as offload when A/P is engaged and STS. This code already required to be designed to high standards.
Conclusion a) We may need to rely less on critical crew action, but there must be some base level that can be counted upon. I suggest at least:
- RTO for engine out below V1
- Pull for takeoff somewhere near Vr
- Gear and flap management and coordination with associated speeds throughout flight
- Comply with ATC guidance
- Ability to navigate to destination
- Ability to capture and follow glideslope and localizer to runway and command landing flare
- Recognize unstable approach and execute go-around
- Sorry for the length of this list. My point is that there are many pilot actions we count on to maintain safe operation
Conclusion b) I fully agree and suggest adding that if the inputs are garbage the system should be robust enough to maintain safety.
I just want to thank you for your valuable contribution to this topic. You are the person here who have given by far the most amount of factual information regarding the exact functionality of the MCAS system and how this system was developed.
Thanks!