Gums et al,
Boeing admits flaw in 737 Max flight simulator
Re ‘like other 737’, stability ‘enhancement’, or anti stall.
First point, this discussion is probably in the wrong thread. Second, there is very little definitive information on these aspects (see Boeing refs), thus supposition reigns. Third, using what is known about an aircraft to build a simulator is not the same as taking a simulator and inferring what the actual aircraft characteristics are, but there ominous indications in this instance.
‘
Like other 737’, is more of a marketing or commercial argument; as such it could be managed by other means (even if not saving $1M per a/c).
‘
Stability vs stall’; the critical points are when and where. Any problems with stall ident - the point of stall, or characteristics at that point, or recovery capability, requires quick and forceful action, loud and positive, thus stick push or similar.
‘
Anti stall’, not a good term, is more associated with stability, usually prior to stall warning - stick shake; awareness, but not always with action.
I conclude that MCAS is a requirement of stability certification, quiet and subtle background enhancement, ‘dressed-up’ to placate customers. Note the use of AoA vs speed input, flaps up only, and Mach input to manage what appears to be a complex problem in a small part of the flight envelope - wt, cg.
The trim input was intended to be small, incremental, and unobtrusive. The design theory appears to be OK, the engineering implementation, checking, and certification a disaster.
MCAS should not be compared with STS, or even Mach trim; nor its implementation as FBY.
I agree with gums # 36 …
Stability involves ‘feel’, measured as stick force in certification.
As an explanatory description only: consider trimmed flight at constant speed, constant thrust. Enter a turn without changing trim position or thrust (aircraft will descend). The ‘feel’ increases as a pull force; this can be assessed at various bank angles - different AoA.
Repeating these tests for a range of speeds (different trim speed) there should be a consistent relationship between bank angle and pull force. Inconsistent force - reduced pull force with bank angle, or with speed decrease at constant bank angle, could add workload in manual flight.
In extreme, slowing down in a turn or level flight at constant trim should always require more pull force, if not the aircraft feel is an unnatural ‘push to turn’. In some cases reducing forces could tend to oscillation or pitchup. There could be similar interactions with thrust - altitude.
MCAS “
will not be a significant issue after modification”, nor require hands-on training except if the handling in the failed state is significantly degraded - cruise flight only. [opinion]
The important issues arising from the simulator mistake are in the processes of checking and certification of training simulators, and the possibly of a shortfall in knowledge about the aircraft, particularly the effect of trim failure.
Gums, [engineering or aerodynamic fix] Instead of lengthening the undercarriage, Boeing should have put the engines on top of the wing [/ fix]
