Originally Posted by
BrandonSoMD
I think that deserves some clarification. I don't fully agree.
I'm a 30-year flight test engineer and am currently helping to rewrite the handling qualities flight test manual for the US Navy Test Pilot School. We focus more on military than transport aircraft, but we do test and fly 737-derivative airplanes (P-8A Poseidon and the C-40 Clipper) and the test methods are universally applicable.
Windup turns are done with set thrust, yes. Power is set as required to maintain the specified airspeed. What is being compared is the response of the airframe to increasing AOA or g at a fixed airspeed, and throttles are fixed during the maneuver to avoid contaminating the results with another independent variable. Several things can be learned from WUTs, including control force or deflection as a function of load factor or AOA, buffet characteristics as a function of AOA, and structural characteristics as a function of g.
While each test point is conducted at a specific power setting, the tests are typically conducted at a range of power settings. This provides a chance to assess the effect of power setting on the various aforementioned characteristics.
MCAS is (at the core) merely a trim application system, designed to reduce the control forces which develop at higher AOA and g with the new-and-repositioned engines. As such, it is a handling qualities difference that is definitely related to thrust line changes. Those differences would typically be revealed by a series of WUT test points. In this case, a WUT at high thrust would be worse, because of the increased pitch-with-power tendencies.
That is all good and well, and always works when all sensors are giving you and the systems the correct information.
AF447 => An iced over AOA probe gives false info, and it does not matter what happened the next minutes, they never figured out in time what the actual problem was.
The B-2 crash => See? With failing sensors there simply is NO TIME.
The X-31 crash => (Where pitot anti-ice was not connected) => The plane goes out of control SO FAST, the only way out is to eject.
When given false information from failing sensors, (and not knowing it) or the failure codes redraw so fast on screen that you simply can not keep track of all of them => It is game over.