Not quite right, but almost.
WARNING: Long post, but as informed as I can make it for those who care to know...
Because the LEAP engine is further forward and elevated (it is HUGE compared to an NG motor), as the aircraft approaches a stall, this engine location EXACERBATES the stall problem because the engine is now FORWARD of the center of lift on the wing. This means the lift created by the shape and location of the Leap engine actually helps “lift and rotate” the aircraft (nose up, tail down) around that center of lift, so MCAS TRIMS THE AIRPLANE NOSE DOWN TO REMOVE THAT EFFECT. Any additional thrust would also further exacerbate the nose UP rotation, due to the large under mount engines, without nose DOWN trim, which MCAS is designed to enable.
The problem with MCAS arises because of THREE ISSUES:
1) MCAS receives SINGLE CHANNEL Angle of Attack (AOA) data, which means ZERO REDUNDANCY, and an erroneous AOA input can make the system THINK there is a stall that doesn’t actually exist, and
2) When MCAS engages, it trims the nose down 2.5 degrees. Depending upon speed and current ACTUAL pitch (it appears the single AOA input is not giving actual data, as it may not have rotated with the airflow or is simply generating erroneous zeroes and ones), this can be very significant. It is also capable of trimming FOUR TIMES MORE THAN THEY TOLD THE FAA IT WOULD TRIM!
3) As you may have seen from flight profiles, flight crews have managed to “wrestle” with this system before crashing. However, perhaps the MOST INSIDIOUS PART OF MCAS is that as a pilot works against MCAS, possibly by trimming AGAINST MCAS’ nose down trim, MCAS RESETS ITSELF. As soon as a pilot stops pulling back or trimming nose up, MCAS LOOKS AT THE SYSTEM AND SAYS “OK, I’M STILL APPROACHING A STALL, SO HERE COMES ANOTHER 2.5 DEGREES (4x reported) OF NOSE DOWN TRIM!!” This repetition is what overcomes pilots and is a KILLER!!
It appears that the only way to stop MCAS from killing you, once you get into this “pitch down, attempted recovery, pitch down another 2.5, attempted recovery” is to break the cycle by using the STAB TRIM CUTOUT switches to the right of the throttles on the forward throttle quadrant. And, you need to do it before about the 3rd time MCAS (which is invisible to the pilots, but can give you this erroneous, consecutive, additive and thus deadly nose down trim position) kicks in or you may not have enough time to HAND CRANK THE TRIM BACK TO A MORE NORMAL SETTING BEFORE GROUND CONTACT OCCURS.
So, even if you figure out the problem, your speed and altitude at the time of working the solution MAY have already doomed you! That’s not a good place to be!
For those of you seeking more info, The Seattle Times has been running some EXCELLENT AND DESCRIPTIVE stories on the system and the institutional failures. Also, the American Airlines Pilots Association (APA) has an excellent video as part of a Washington Post piece.
If this place made posting pics easier, I have a few pictorial explanations of the above.
FWIW, I was supposed to fly the MAX-9 (my airline only has -9s, no -8s) the morning after they were grounded. It would have been only the 4th time I flew it, as we only have 14 of them. We are supposed to receive well over 100 of them over the next few years (about 1 per week), to included the even newer -10 derivative!
Believe it or not, this problem has its roots in the 737-100, designed over 60 yrs ago, which had to be super low to the ground because it used to be boarded by using a metal ladder which came out from a compartment under the forward boarding door. At that time, the engines (used on the 100 and 200) were old “cigar shaped” noisemakers.
When Boeing developed the 300/400/500 models, they used new high bypass turbofans from CFM to improve efficiency. Many of you will have noticed they have the strange “flat bottom” which only sits about 17” above the ground. A round inlet could not get certified, as it would have constantly hit the ground in crosswinds or even possibly a hard landing, and it was imperative the aircraft had the same 737 type rating for crews.
Fast forward to the NGs (700/800/900) and you have greater efficiencies (16%), faster normal cruise speeds (M.785 vs M.75) and larger cabins ($$$).
Airbus then creates the A320NEO family and it is a roaring success, so Boeing needs a competitive response. They quickly develop, test, and approve an almost completely new aircraft (new interiors, new engines, new cockpit forward displays, new winglets...) BUT THEY NEED TO KEEP IT AS A 737 “TYPE RATING” or else it will be far too expensive for 737 operators to absorb into their fleets!!!
The FAA approves of allowing BOEING to test and certify considerable parts of the program, with very limited oversight, due to FAA (US Govt) budgetary concerns and the lack of certified engineering staff at the FAA. MCAS is approved, but NO ONE TELLS THE AIRLINES AND THE ENTIRE SYSTEM IS OMITTED FROM THE 737 MAX AIRCRAFT FLIGHT MANUALS APPROVED FOR AIRLINES BY THE FAA!!
Airlines receive a 56 minute video detailing “Differences” between the NG and the MAX, but this merely discusses the differences you SEE and some of the systems they put in place to make the MAX “feel and fly” like the NG.
For instance, the engines are much bigger, so they are further forward and attached higher on the wing. In addition, the nosegear is 8 inches higher to lift the nose (and thus the bottom of the engines) away from the ground during taxi, takeoff and landing! This creates a little problem, as it changes the “sight picture and landing attitude” of the aircraft.
So, Boeing added onto the normal spoiler system to allow them to purposely “float” during landing, while also recommending a Flaps 40 landing (usually most people use F30, except for low visibility or very short runways).
This “system” (or “rigging OF the system”) is designed to make the sight picture on landing look “normal” to an experienced NG pilot, while also keeping approach speeds (which can reach over 160Kts, or 185mph) within a range that will allow only FOUR WHEELS to provide enough braking power, when added to the reverse thrust, to stop the aircraft. For certification purposes, and so we can still fly when the reversers are inoperative, the aircraft has to be certified using brakes only!
So, ALL THE PROBLEMS ON THE MAX ARE BECAUSE AIRLINES (SOUTHWEST, IN PARTICULAR) DEMANDED AN AIRCRAFT THAT WOULD PASS THE FAA’S “COMMON TYPE RATING CERTIFICATION” for an airplane that began life over a half century ago!!!
Indeed, while engines...and MCAS, etc...have all been updated and modernized, you may enter a 737 flight deck, look at all the post-WWII toggle switches on the systems panel above the pilots, and think you have stepped back in time.
For many of us, the 737 NG is a completely different animal than the old 3/4/500s, but we all felt they had stretched it to the limit with the -900ER. Today, many of us feel like they have stretched it to the point of breaking it with the MAX...and that’s before you get to the MAX-10, which is going to require an origami style landing gear extension and retraction due to size!!!
New cockpit displays have things in different places than they’ve been for decades. Aircraft sits higher on the ground. Engines are massive and require a long period of motoring (turning without igniting) to straighten out their shaft (as it warps when it cools!!!) before starting. They take a long time to start, then a long time to warm up before you can takeoff! And on and on and on...
As professionals, we accept that management manages, and we fly. We all (manufacturer, airline, pilots) usually work cooperatively to ensure safety systems are in place so we can have safe, consistent, global operations through SOPs we’ve developed together through decades of experience.
Then, this new aircraft came along, and Boeing rushed it into service as a competitive response to the thousands of A320NEO orders it was losing from traditional Boeing customers. However, Boeing had ZERO AIRCRAFT FLIGHT SIMULATORS that could replicate the 737MAX FLIGHT CHARACTERISTICS, so the airline simply pushed a 56 minute video to our company iPads (which contain all our flight manuals, performance data, etc.) and set up a 2 hour Computer Based Training module we were required to watch before we received any of the aircraft.
Then, MONTHS LATER, if you were scheduled to fly one, you were expected to review all that information, including 444 pages (IIRC) of “Differences” information before flying it!
Sadly, the fatal flaw in this whole grand scheme to save money on certification, training and time was that THEY DID NOT HIGHLIGHT A SIGNIFICANT AND POTENTIALLY DEADLY FLAWED SYSTEM THAT WAS ON NO OTHER AIRCRAFT IN THE WORLD! THEY MADE UP MCAS BECAUSE THIS AIRPLANE WOULD TRY TO EXACERBATE A STALL WHILE YOU WERE TRYING TO ESCAPE IT!!!
(Read that again for good measure!!!)
You decide how you feel about Boeing, the FAA, and whether the changes made to this aircraft should require FULL MOTION SIMULATOR TRAINING TO INCLUDE THE RECOGNITION AND REQUIRED RESPONSE TO A SYSYEM THAT MIGHT KILL YOU AND WHETHER IT SHOULD BE DESIGNATED AS A DIFFERENT AIRCRAFT TYPE FOR THE PURPOSES OF TRAINING AND CERTIFICATION OF FLIGHT CREWS, WHO MAY ONLY SEE THIS AIRCRAFT ONCE EVERY FEW MONTHS COMPARED TO THE LARGE FLEET OF 737NG AIRCRAFT THEY’VE BEEN FLYING FOR YEARS?
You might be able to ascertain my feelings at this point. I am very, very sad to hear what happened to the people on both aircraft, and am eternally grateful I have not been faced with what they encountered.
I’d like to think I would have used the STAB TRIM CUTOUT switches after the first indication of an abnormal aircraft response, but I think the Lion Air crew were dead the minute it activated because they had no idea what they were facing.
The Ethiopian crew may have had an idea, but who knows what they were actually faced with, including aircraft instrumentation, warnings (aural and or visual) and their ability to actually counteract a system that was DESIGNED to add to their woes the minute you thought you had it under control.
That could have been me, and that REALLY pisses me off!
The worst part is, when I did fly it, I thought it flew beautifully. However, behind all of that smoothness, it appears all the automation that makes it feel so responsive was just hiding a deadly flaw that was literally waiting to try to kill me and everyone else onboard IF THE SINGLE AOA INPUT TO MCAS FAILED!!
One AOA vane on the outside of the aircraft, below the Captain’s side window, should not be able to do what it can do on this aircraft. There should always be redundancy (two AOA inputs, and if they do not agree, the system is removed from operation, with a warning that you have lost at least 1 AOA input AND that the MCAS system is inoperable so avoid coming anywhere close to a stall attitude...lower pitch climbs, lower altitudes and greater stall buffet margins at that lower altitude, etc, etc.) until you got on the ground and could get it fixed.
If you got this far, my apologies for the length of this post. I hope it was helpful to those who care.
EDITED AND ADDED: Someone just sent me this link to a British 737 Systems website:
http://www.b737.org.uk/mcas.htm
Info is cobbled together from numerous sources I’ve previously seen, but has a decent summary up top.
