Leeham News covers commercial aviation, with analysis of Boeing and Airbus aircraft, safety, and engineering.
HN commenters cite it for 737 MAX analysis and for a Boeing insider's account of the door plug, which they say the official report later confirmed.
Prior to MCAS, most causes of trim runaway could be stopped by countermanding it with the control column, but, because MCAS is intended to avoid a pilot-commanded (though presumably accidental) stall, this is not the case for MCAS:
"[MCAS intervention] can be stopped by the pilot counter-trimming on the yoke or by him hitting the CUTOUT switches on the center pedestal. It’s not stopped by the pilot pulling the yoke, which for normal trim from the autopilot or runaway manual trim triggers trim hold sensors. This would negate why MCAS was implemented, the pilot pulling so hard on the yoke that the aircraft is flying close to stall." [1] [my emphasis.]
So it seems we may have several issues here:
1) Prior to MCAS, trim stab cutout was almost the last-ditch option against trim runaway (there was one more: grab the trim wheels and physically prevent it), but it became the only way to deal with an MCAS-commanded runaway (other than grabbing the trim wheel.)
2) Boeing did not reveal this prior to the inquiry into the Lion Air crash, despite the fact that it introduced a new experience of trim runaway that differed from what pilots had been trained to expect.
3) The Boeing / FAA response to the Lion Air inquiry was an Airworthiness Directive that basically said "pay attention to what we said before about handling trim runaway" (though, whether or not Boeing / FAA made a point of it, pilots may well have become aware of how MCAS runaway differed from their prior training -- that…
As someone who has actually flown on the Concorde, I can say that I'd gladly endure its tight seats again and empty my wallet in exchange for a shorter flight. Heck, if I had the option between spending $20,000 for a NY-London roundtrip on an Overture (the same price for that route on the Concorde, inflation-adjusted) versus spending $20,000 to charter a long-range private jet (likely a significant underestimate), I'd go for the Overture in most cases.
However, although I'm rooting for any company that's making a sincere (as opposed to fraudulent) attempt at bringing back supersonic travel, the hardest challenges may still be ahead for Boom. The biggest one is the need to find or build a new engine. They've recently redesigned the Overture to use four engines instead of two, which should ease required engine specs, but there's no engine that would meet the reliability, noise, fuel consumption, and dimension requirements for a supersonic passenger aircraft.
Related to the engines: money. It sounds impressive that boom raised at least $150 million, including $60 million from the US Air Force (which has the added advantage of creating a new customer segment in the military)... until you learn engine development alone would require in the ballpark of $6 BILLION of capital. Aviation history is rife with examples of amazing, innovative aircraft designs that failed because no suitable engine was available.
Also, Boom leadership has set some ambitious goals, which makes me a bit…
"All of the above"
The MCAS itself did exactly what it was programmed to do. One of the sensors feeding it, which was not redundant (!), malfunctioned, and MCAS acted on the data - garbage in, garbage out.
By not having sufficient redundancy, MCAS was designed in a failure-prone way. This was justified because the failure would be like another kind of known failure mode (runaway trim), and pilots already had a checklist for it (the key point being to turn off electric trim).
The problems with that are:
1. The problem a malfunctioning MCAS (acting "correctly" based on bad data) introduces is intermittent/erratic, making it harder to correctly react to it. Especially since the pilots weren't aware that a system that would act like this was on board!
2. Humans make mistakes in high-stress situations, which is why accepting something that introduces additional problems and relies on humans to handle them is a bad idea.
3. Turning off the electric trim also made it hard for the pilots to correct the situation, as it disables the manually-controlled but motor-powered trim. One theory is that the forces may have been too great for the backup solution (trimming manually) to work, a situation that old (but not current) manuals addressed.
MCAS has a limit how much it will trim, but any trim input by the pilot resets it, and lets it move the trim by the limit amount again.
This is just a layman's interpretation:
From the flight data recorder, it seems like the Ethiopian ET302…
Ironically, I believe that your information is also inaccurate. MCAS is required in order to meet federal airworthiness requirements. Without it, in certain flight conditions the back-pressure on the control yoke gets less as the yoke is pulled further back. It's like over-steer in a car, and is simply not allowed. Yes, the plane is dynamically stable; if you leave the yoke in one position it won't pitch up even more. However, the forces must be corrected somehow, regardless of type rating concerns.
"The 737 MAX was a bit too easy to pull into a stall when flying with high AoA and making abrupt maneuvers. The larger engines for the MAX hung further forward from the wing, added a destabilizing aerodynamic area ahead of the center of gravity, destabilizing the pitch moment curve at high AoA.
Boeing and the certification authority, FAA, decided added margins was called for. Boeing added a pitch augmentation at high AoA called Maneuvering Characteristics Augmentation System, MCAS.
The aircraft should trim nose down to increase the stick force needed once it passed into the light grey area where the base aircraft had a region of less stability. Before the augmentation, the pilot felt if the aircraft wanted to fly into the stall, it got easier to increase the AoA after 12°AoA. With the augmentation the felt extra force was the same for the first and last part of the curve before the maximum lift was achieved at stall (and stall warning kicked in)." [0]
The manner of the fix…
This thoroughly vindicates what the anonymous whistleblower on the internet was saying:
https://leehamnews.com/2024/01/15/unplanned-removal-installation-inspection-procedure-at-boeing/#comment-509962
> Current Boeing employee here – I will save you waiting two years for the NTSB report to come out and give it to you for free: the reason the door blew off is stated in black and white in Boeings own records. It is also very, very stupid and speaks volumes about the quality culture at certain portions of the business.
> A couple of things to cover before we begin:
> Q1) Why should we believe you? A) You shouldn’t, I’m some random throwaway account, do your own due diligence. Others who work at Boeing can verify what I say is true, but all I ask is you consider the following based on its own merits.
> Q2) Why are you doing this? A) Because there are many cultures at Boeing, and while the executive culture may be throughly compromised since we were bought by McD, there are many other people who still push for a quality product with cutting edge design. My hope is that this is the wake up call that finally forces the Board to take decisive action, and remove the executives that are resisting the necessary cultural changes to return to a company that values safety and quality above schedule.
[...]
> However, more critical for purposes of the accident investigation, the pressure seal is unsurprisingly sandwiched between the plug and the fuselage, and you cannot replace it…
Reading a lot of detailed reports, I concluded that nobody at Boeing ever properly tested the conditions that happened by both Lion Air and Ethiopian, until much after the second crash. Boeing didn't do enough steps to reconstruct what happened by Lion Air, otherwise they would have never published totally useless procedure which was then followed by the pilots of Ethiopian. The actual testing in the proper simulator would have shown that the emergency procedure, as written by Boeing after Lion Air crash, just can't work.
The pilots in Ethiopian and all the passengers paid with their lives for a whole world to learn that.
The world knows because one pilot tried to partially reconstruct the conditions on his own in an older simulator, as there were effectively almost no new simulators because the Boeing's selling point was that the new model of the plane is same as an old one model, just to avoid the recertification and pilot retraining. So the said pilot did the test for youtube, showed that what the pilots probably did matched the emergency procedure, and that exactly that following the procedure most probably results in the crash, but had to remove the video once his employer became aware of what he did.
I've posted the link to that original source then, but HN moderators marked it then as a "dupe":
https://leehamnews.com/2019/04/03/et302-used-the-cut-out-switches-to-stop-mcas/