Originally Posted by
john_tullamarine
I believe the certification required a higher force to signal to the pilot the approach to the stall - enter MCAS.
Greetings, good sir. - I trust you and your good lady continue to enjoy retirement life.
The LSS concern is across the speed spectrum, where the pilot needs to feel more pull - the further below trim speed - or push - above trim speed - for the stability considerations to be acceptable. It's not really a relation to specific speed, stall or otherwise. Unfortunately, some aircraft, especially at lower speed/high alpha, and high thrust, can see the "up" lift force at the front of the engine installation cause a nose up pitch contribution which reduces the pilot's pull force requirement when the aircraft is below trim speed.
As I indicated previously, I am aware of one aircraft for which the effect, in the absence of the SAS's influence, is to reverse the force gradient with speed and the pilot ends up having to reduce the pull force/push the stick to avoid a further reduction in speed. While that is flyable, it is not a good situation, requiring some out of left field knowledge and a very high level of concentration by the pilot. In general, the TP will rise to the occasion, while the rest of us would tend to fall by the wayside ...
As I read the tea leaves, the usual SAS systems and MCAS are looking to address the same concern, albeit by slightly differing techniques.
Hi JT, but it seems MCAS was to address a concern and 0.6 units was fine, but then later in the program another concern was encountered in flight testing. This required the supercharged MCAS of 2.5 units and faster to resolve.
There is very little information but it seems the first was for the stick feel certification issue, the other not mentioned as a stick feel issue but more a stability issue (possibly a stall issue).
The second has had very little commentary, but if true is possibly by far the greater issue to have and deal with.
From what I can work out the MAX has issues with high speed, high AoA in a turn having "correct feel" & low speed and high AoA - C of G and weights have effects as do G forces.
However a little flap or the autopilot fixes everything (all of the issues). I find this a little hard to fathom, but will agree the auto-pilot does not care for the stick forces getting light. At some stage the auto-pilot will just hand over the aircraft to the pilots in a flyable condition or not.
I spoke to my cousin that I think knows a bit about computers and software, if he knew about the Max he said yes he was following it (not on here). I asked him about the "fix" and what time frame he thought. The following is his reply.
"To be honest, I doubt it will be fixed, we'll just be told that it has been and something will be cobbled together. These problems are complex, and Boeing have sacked most of their senior knowledgeable engineers (the bit in that article about critical systems relying on only a single sensor input shows that design checking was absent from the process, leading to larger costs to fix such shortcomings). I spend a lot of my life fighting complexity creep in IT systems for primarily this reason (and why the stuff I write tries to follow Einstein's maxim of "as simple as possible, but no simpler").
The part in the original article about "No longer needing engineers because the software is mature" is typical management thought process, completely missing the point that this software is continually being changed for changing airframes.
I actually have a subconscious fear of riding elevators for this reason, knowing that the control systems are no longer written by seasoned professionals, but interns or otherwise."
My sister asked this - "Aside from stopping abruptly or I guess going really fast what issues are there to be worried about on an elevator that malfunctions?
I feel like I have limited thinking in this area if you have a subconscious fear. Are they likely to become rabid and eat us?"
His reply was this - "Or not stopping abruptly. The emergency brakes should be hardware interlocked, and independent of computer control, but cost cutting will end up with another
https://en.wikipedia.org/wiki/Therac-25 on our hands. A lot of the software is not open to public scrutiny (locked up on the grounds of "proprietary"), so we have to trust people to write software with minimal bugs, but the pressure to market ensures that it's typically rushed. Boeing were initially denying that anything could be wrong with their software until the death of two plane-loads of people and mounting evidence forced them to admit their defects".