J.Edward

exploerWannabe - I find myself in partial agreement with your post. To state the obvious - I do not think there is anything inherently wrong with the 737-1/2/3/4/5/6/7/8/9s.

What I find myself in disagreement is the degree argument the 737MAX = 737 classic or any of the subsequent designs and therefore carries forward in safety record of those prior designs.

Consider MCAS: the reason Boeing added it was to make the MAX "feel" like the NG. What was one of the reasons the MAX did not "feel" like the NG? The change in relative placement of the engines to accommodate the space required for a higher bypass ratio allowing for greater fuel efficiency. Why even attempt to make the adjustment to the way the MAX felt? To make the MAX more attractive to buyers by reducing certification costs and complexities.

Please do not read the above as judgement one way or the other on MCAS, rather I put it forth as evidence the MAX ≠ 737NG.

Sooner or later the individual must decide what's in his or her best interest based on whatever data s/he has.

Can you or I make an authoritative statement as an aerospace engineer, pilot, government regulator, etc. - probably not as I assume neither of us are.

BUT we both can make an individual decision based on our own beliefs, values, interpretations, prejudices, etc. as to whether or not we will trust a MAX with our individual lives. My take is "no, I do not trust the MAX nor the systems designed to ensure my safety to accurately assess the MAX with my life" but I certainly also understand how a reasonable person can reach a different conclusion. I suspect in time my views could evolve but for now it is not worth the risk I perceive to continue to be a beta tester for Boeing when the price of failure is so high. I'd also point out in this context we can both be _r_ight even if we arrive at different conclusions - and that's okay.

FWIW it is not my intent to convince you my interpretation of the situation is _R_ight (and truth be told, it's probably wrong on some aspects) and I certainly understand how others, drawing on the same data, can reach other conclusions.

jsloan

The MAX is a 737. It is certified under the 737's operating certificate. You can disable the electric flight control systems and operate it manually.

But it isn't evidence of that. If you drive a Nissan Maxima, and you activate "Sport" mode instead of standard driving mode, you're still driving a Nissan Maxima.

A runaway horizontal stabilizer is a possible mode of failure on the 737NG. It appears to be more likely on the MAX -- hence the forthcoming MCAS changes -- but it's not a new problem.

Ultimately, every passenger is trusting the pilot to be able to react to a runaway stabilizer -- not just on the MAX, but also on the NG, and on the A320 series. In fact, I believe the procedure for runaway trim is exactly the same on all of them: disengage the automatic stabilizer and turn the wheel to trim by hand. (The A320 trim wheel is hydraulic-assisted, but other than that they appear to be the same). If pilots fail to follow the correct emergency procedure, on any of these aircraft, the results are likely to be catastrophic.

exwannabe

But the FAA notice post Lion put a different procedure in place for the MAX than the other 737s.

For the non MAX's, the pilot disengages the auto-pilot and tries to correct via the tabs that activate electric control. Only if that fails does the pilot disengage the entire electric control system and use the hand crank.

For the MAX, if the pilot determines the reason is likely based on the MCAS going haywire, they can use the tabs to bring it in trim, but then they immediately shut off the electric system and use the crank.

The reason for difference is that on the MAX the pilot might think they have it under control, and would not know that the MCAS is going to come back with a vengence shortly. And by then they will have lost key time.

Different recovery based on the MCAS, and pilots were being kept in the dark about it.

Maybe somebody can nit-pick me that I did not write this exactly correct. But that a decently long section in the manual specific to the MAX was added should make it clear there is a difference.

Arguably post Lion they should have known.

DenverBrian

Poor analogy. "Sport" mode on a Nissan Maxima isn't there to prevent a failure mode in the car. "Sport" mode isn't there because the government would require Nissan to create an entirely new model name without it.

fly18725

DenverBrian

MCAS specifically noses plane down in certain conditions. For what other reason do you have a system (other than the pilots themselves) nosing the plane down?

Newman55

LarryJ

The service bulletin, which became an airworthiness directive, explained what would happen with an unscheduled MCAS activation and emphasised that the existing runaway stabilizer procedure should be used. None of the steps in the procedure were changed.

Additional information was added to the end of the MAX checklist which gives more detail on the correct techniques to use and the associated warnings that could accompany an invalid AoA input. This additional information is the only difference in the runaway stabilizer checklist on the NG and MAX.

LC757

Or perhaps you and others have been arguing under a false assumption that it's not. https://www.nytimes.com/2019/06/01/b...max-crash.html

tl:dr Many have argued that MCAS existed as a way to correct a "light" pitch feel caused by certain AoA conditions, not related to an anti-stall measure. This is true - for the first, well publicized version of MCAS that Boeing made aware of to pilots and the FAA.

However, MCAS was revamped, by a much smaller group of engineers and decision makers, to be more aggressive and account for poor handling in low speed stall situations after a test pilot's concerns. This change also led to MCAS activation being triggered by a single AoA sensor. This was not a revamp that Boeing made aware to many - including the regulators who certified the plane under the assumption that the original version MCAS was still the final incarnation of it.

BF263533

Isn't there an issue that human force at times cannot turn the manual wheel? Possibly an electric or hydraulic assist on the wheel may be needed?

jsloan

Neither is the MCAS. Both "sport" mode and the MCAS merely adjust the vehicle's handling.

If the role of the MCAS were to prevent a failure, it stands to reason that it would be enabled when the autopilot is engaged. It's not.

People who have attempted to simulate the ET flight did run into that problem, yes. However, preliminary reports indicate that the ET flight was going much, much faster than it should have been (that affects the force required to turn the wheel), and that the problem wasn't detected until the stabilizer was extremely far out of trim (that affects how far you need to turn the wheel). If you disengage the electric stabilizer when at the correct speed and at (or near) trim, you don't need superhuman strength to turn the wheel.

All aircraft can be maneuvered into unrecoverable situations if the right sequence of failures occurs. The goal of an aircraft designer is to make that sequence as improbable as possible.

COSPILOT

DenverBrian

Would the FAA have certified the MAX without MCAS? If so, why would Boeing spend the extra money to include it?

jsloan

No, because the handling characteristics are part of the certification. That doesn't mean it's intended to prevent a failure, except inasmuch as having a different feel could cause a pilot to oversteer.

DenverBrian

And yet 350 people are dead, it's linked to MCAS, and the planes are still grounded.

That doesn't sound like a "handling characteristics" feature that had a little hiccup.