XRAYretired wrote:PixelFlight wrote:XRAYretired wrote:Objective of 2 is achieved by implementing 3 i.e. the maximum deflection is limited to 2.5deg which is less than the maximum elevator authority.
I agree that you might be right on this, but I am unable to find a document that confirm this. If you have, please share.
My reading is that the 737 uk fix number 2 description is that the 0.6 degree and 2.5 degree was part of the text that describes MCAS v0 ("In its original report, Boeing said") and MCAS v1 ("However, after the Lion Air crash, it told airlines"). So the MCAS v2 fix number 2 description strip down to "To limit how much MCAS can move the horizontal stab to guarantee sufficient handling capability using elevator alone". There is no mention anymore of a given number of degree. To me the MCAS v2 fix number 3 is unrelated to the fix number 2. Please correct me where I am wrong.
Suggest you go back to the Boeing released , layman terms, outline:
'The additional layers of protection include:
-Flight control system will now compare inputs from both AOA sensors. If the sensors disagree by 5.5 degrees or more with the flaps retracted, MCAS will not activate. An indicator on the flight deck display will alert the pilots.
-If MCAS is activated in non-normal conditions, it will only provide one input for each elevated AOA event. There are no known or envisioned failure conditions where MCAS will provide multiple inputs.
-MCAS can never command more stabilizer input than can be counteracted by the flight crew pulling back on the column. The pilots will continue to always have the ability to override MCAS and manually control the airplane.'
The final statement equates to item 2 in the Chris Brady write up. This s a description of achievement of limiting activation to one cycle if the AoA has not dropped below the trigger value.
The rate of change of trim was specified as 0.27deg/sec noes down for V1.0, (and a cycle length of 9.26 seconds). This was the rate arrived at to induce the desired effect. Unless the aerodynamics have changed (and nobody knows about it), it does not change. In any case the total deflection is equivalent to 2.5deg nose down in one cycle and is within the authority of elevator to counteract, so there is no reason to change anything else if MCAS activation is limited to one cycle.
Sorry, but if limiting the rate and time to 0.27deg/sec and 9.26 seconds effectively limit the displacement of 2.5deg, this do not take in account the initial position of the stab trim, and it could anywhere already, including near the elevator authority limit.
The second thing I found curious is that according to your description, the fix "elevator authority" (in normal condition) would then depend on the fix "only one input per AoA event in non-normal condition". My understanding is that in normal condition the MCAS v2 is still allowed to provides multiple inputs, so it is still able to take authority overt the elevator if not limited by something else. In normal condition this should be the right thing to do, but this do not match the fix description. Confusing for me.
I would not be surprised that the actual implementation of the MCAS v2 is a bit more complex to grant the elevator authority (in normal condition).