MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures

[infrequentflyer789]

Originally Posted by OldnGrounded

From the report:

Recommendation R3.4:

The FAA should review the natural (bare airframe) stalling characteristics of the B737 MAX to determine if unsafe characteristics exist. If unsafe characteristics exist, the design of the speed trim system (STS)/MCAS/elevator feel shift (EFS) should be reviewed for acceptability.

Emphasis added.

Yep, this all looks to be tied into the change to MCAS activation (and power) subsequent to first flight. It looks like JATR cannot determine whether or not this is the case because there is insufficient documentation around this change - as they complain about elsewhere (not only documentation not reaching FAA, as already reported elsewhere, but things like safety analysis not updated).

Elsewhere I noticed they refer to "...reducing the pitch-up tendency..." - now I don't think "pitch-up" is the same as "stick-lightening" (is it?), and I'd expect this report to make the distinction - if they really mean it pitches itself up into stall (at some point) then MCAS really is stall prevention/protection and that will open a truckload of worm cans.

[MemberBerry]

This is the section of the JATR report discussing the relation between stall behavior and MCAS, I highlighted the parts I found interesting:

• Recommendation R3.4: The FAA should review the natural (bare airframe) stalling characteristics of the B737 MAX to determine if unsafe characteristics exist. If unsafe characteristics exist, the design of the speed trim system (STS)/MCAS/elevator feel shift (EFS) should be reviewed for acceptability.
  • Observation O3.4-A: The original implementation of MCAS was driven primarily by its ability to provide the B737 MAX with FAA-compliant flight characteristics at high speed. An unaugmented design would have been at risk of not meeting 14 CFR part 25 maneuvering characteristics requirements due to aerodynamics.
  • Observation O3.4-B: Extension of MCAS to the low-speed and 1g environment during the flight program was due to unacceptable stall characteristics with STS only. The possibility of a pitch-up tendency during approach to stall was identified for the flaps-up configuration prior to the implementation of MCAS.
  • Finding F3.4-A: The acceptability of the natural stalling characteristics of the aircraft should form the basis for the design and certification of augmentation functions such as EFS and STS (including MCAS) that are used in support of meeting 14 CFR part 25, subpart B requirements.
• Recommendation R3.5: The FAA should review 14 CFR 25.201 (Stall Demonstration) compliance for the B737 MAX and determine if the flight control augmentation functions provided by STS/MCAS/EFS constitute a stall identification system.
  • Finding F3.5-A: The nose-down pitch identified during Boeing flight tests for stall appears to the JATR team to be the product of system augmentation with flaps and gear up, and is likely due to stabilizer motion from the MCAS function.
  • Finding F3.5-B: The FAA-accepted Boeing flight test technique of freezing column deflection at the onset of EFS was perceived by the JATR team as possibly not meeting the requirements of § 25.201 for natural stall identification from nose-down pitch, not readily arrested. Column/elevator deflection data indicates that there may be an insufficient column input to attempt to arrest the nose-down pitch created by system augmentation.
  • Finding F3.5-C: The JATR team considers that the STS/MCAS and EFS functions could be considered as stall identification systems or stall protection systems, depending on the natural (unaugmented) stall characteristics of the aircraft. From its data review, the JATR team was unable to completely rule out the possibility that these augmentation systems function as a stall protection system.
• Recommendation R3.6: The FAA should review the use of non-standard flight test techniques, such as freezing column position at EFS actuation, when showing compliance with 14 CFR 25.201 (Stall Demonstration). The use of non-standard flight test techniques may not meet the associated regulatory requirements.
  • This recommendation is based on Findings F3.5-A, F3.5-B, and F3.5-C, above.
• Recommendation R3.7: The FAA should review how compliance was shown for the stall identification system on the B737 MAX with respect to inadvertent operation due to single failures.
  • Finding F3.7-A: The JATR team considers that system features on the B737 MAX might constitute a stall identification system. This system is vulnerable to inadvertent actuation due to a single failure, which would not meet the accepted guidance contained within AC 25-7C, Chapter 8, Section 228.

I found especially interesting that last finding, F3.7-A, because it would explain why Boeing insists MCAS is not related to stall prevention. This is the AC the report refers to, section 228 is at page 334 of the PDF:

https://www.faa.gov/documentLibrary/...2025-7C%20.pdf

Some relevant parts of the AC:

A means to quickly deactivate the stall identification system should be provided and be available to both pilots. It should be effective at all times, and should be capable of preventing the system from making any input to the longitudinal control system. It should also be capable of canceling any input that has already been applied, from either normal operation or from a failure condition.

And, while the cutout switches can be used to stop MCAS, they don't cancel "any input that has already been applied". Both the original and the "fixed" MCAS would fail this requirement if MCAS is a stall identification system.

Also from the same AC:

To ensure that inadvertent operation of the stall identification system does not jeopardize safe flight, and to maintain crew confidence in the system, it should be shown that:

1. No single failure will result in inadvertent operation of the stall identification system;

The original version of MCAS didn't meet that requirement.

[spornrad]

Originally Posted by OldnGrounded

From the report:

Quote:
Recommendation R3.4:
The FAA should review the natural (bare airframe) stalling characteristics of the B737 MAX to determine if unsafe characteristics exist. If unsafe characteristics exist, the design of the speed trim system (STS)/MCAS/elevator feel shift (EFS) should be reviewed for acceptability.

Emphasis added.

That means in my view: If STS/MCAS/FCC is required for envelope protection, the present dual channel design is in no way sufficient/acceptable. Whether the MAX can be possibly re-certified in the next few months will completely depend on the results of the "bare airframe" test flights.
If the augmentation is only a "stall identification" feature stick pusher type, she may fly.

[Takwis]

A dollar says they'll say it is a stick pusher type system, they won't test it without, and line pilots will get to be the test pilots.

[OldnGrounded]

Originally Posted by Takwis

A dollar says they'll say it is a stick pusher type system, they won't test it without, and line pilots will get to be the test pilots.

Do you think EASA, CAAC and the other CAAs will go along with that?

[gums]

Salute!
Thank you Member...
Well, the chickens are finally coming home to roost.
Mny of us wondered about the basic aero of the new 737 when we found out that Boeing had to add a doofer to require more back stick force ( not movement) as the plane got to "x" AoA. Not stall AoA!!!! An AoA where the requirements dictated increasing back stick as the plane approached "x" AoA. Not stall!! The p;lane already had a shaker to let clueless pilots know something was bad unless releasing back stick. The plane already had a speed/AoA thingie that reversed trim if you wnet faster or slower - STS. So what's another kludge to overcome basic aero problems for cable and pushrod and pulley controls?
I only flew one jet that had the stick lightening as it approched a subsonic stall, And I only felt it once, because I pulled more than I shou have and the wings were buffeting and even rocking a bit. Duhhh? Maybe you should ease off a bt, Gums?

The 737 needs a few test pilots to fly the damned thing with no MCAS or STS activated and then publish the pitch coefficients for AoA versus pitch tendency and control stick force/movement. True transparency. And a few of we lowly pilots might have the technical savvy to understand what the plots were telling us.

Later......

Gums sends...

[Grebe]

The 737 needs a few test pilots to fly the damned thing with no MCAS or STS activated and then publish the pitch coefficients for AoA versus pitch tendency and control stick force/movement. True transparency. And a few of we lowly pilots might have the technical savvy to understand what the plots were telling us.

I agree with gums about 99.9 percent of the time- but this is the .01 percent I have a mild disagree. AFTER test pilots do their thing to get some facts and data
get a dozen or so line pilots to do the same thing ( at altitude of course ) maybe two or three from each airline. This would help spread the word and verify the ' redone' sims are realistic

Maybe could sell tickets for the ensuing ride - call it an "WTF" ticket ?

[gums]

Salute!

No disagreement, Grebe
Some of us are capable of interpreting the aero plots and relating the data to our personal experience in the particular jet.
I like your procedure. I just want to go on record that some of us from the beginning of the thread wanted to hear from actual pilots that actually flew the beast to plot the data that made Boeing implement the MCAS.

As a pilot, I want to be briefed/explained about a new system or newly discovered aero characteristics of the plane I have to get to Topeka Tuesday morning with 150 folks. Better yet, I want to see and feel the plane before and after the new system is implemented.

Gums sends...

[Takwis]

Gums, Grebe, I got to do such a flight...late at night, after my scheduled flying, many many years ago. Maintenance had replaced an elevator pushrod on a -200, and needed a couple of guys to go prove that they did it right, and that the plane would fly in manual reversion. We were chosen. Maintenance rode along, to give us a warm fuzzy. We got up to 33,000, I think it was, and then the mechanic turned off all four of the hydraulic pumps.

ImmediateforcefulpitchupthecaptainandItryingdesperatelytoput allofourweightintoforwardpressureontheyokeallwhileyellingTUR NTHEMONTURNTHEMONTURNTHEMON!!!

The mechanic turned them back on, and we all lived.

OldnGrounded, not without a lot of arm twisting, arguing, threatening, and maybe a little financial pressuring.

[gums]

Salute, Tak !!

replaced an elevator pushrod on a -200, and needed a couple of guys to go prove that they did it right, and that the plane would fly in manual reversion. We were chosen. Maintenance rode along, to give us a warm fuzzy. We got up to 33,000, I think it was, and then the mechanic turned off all four of the hydraulic pumps

On my LEF failure depicted in my bio link on my profile here. is what the maintenance crew forgot to check. The LEF tubing connevted to a hydraulic motor via a "spline" type joint and the tube gradually worked its way out as I taxied and rolled. An FCF may have caught this, but many procedures on the original Vipers did not require a check flight. Even replacing one of the four flight control computers didn:t.

I still wanna se the data from the wind up turns and st-level approach to stall profiles.

The 737 is not the old, antique cable and pulley system many here flew for two decades. Your test hop verifies this.

Gums sends...

[Takwis]

Me too, Gums. Data from a flight in the PLANE, not the SIM.

[MechEngr]

The original version of MCAS didn't meet that requirement.

Technically the stick shaker system didn't either.

MCAS does not alert the crew to an impending stall and, though it may be a stall avoidance system, it doesn't identify the condition.

That pilots and regulators have long accepted a system lying about stall warnings based on the same false inputs that MCAS also depended on has confused me.

[megan]

We have an experienced aviator, Byron Bailey - ex military fighter & 777 & current biz jet, who writes a regular column in our local national paper (The Australian), and had this to say,

Indeed there have been several incidences of MCAS activation on US B737 MAX aircraft but experienced American pilots recognised the problem, which just required treating it as a pitch trim runaway, and turned the switches off.

Question, is what he's saying re MCAS activation cases in the US for real?

[Grebe]

Originally Posted by megan

We have an experienced aviator, Byron Bailey - ex military fighter & 777 & current biz jet, who writes a regular column in our local national paper (The Australian), and had this to say,Question, is what he's saying re MCAS activation cases in the US for real?

Hmmm- maybe its time to take a closer look at the ' typical ' AOA sensor **probably** in use by Airbus and Boeing ?

https://www.satcom.guru/2019/03/aoa-...oeing-fix.html

Note the cheap way of indexing the sensor to the vane - a loose screw can result in odd readings very subtly

In my belt and suspenders world as a SLF-engine-ear - I would think a d shaped shaft or a spline and d ring assembly ( spline for location of sensor- snap or dring to keep on spline ) or similar would have long ago been used- mandated.

[Takwis]

It raises a lot of questions. Why is he the only source? No official notices, from FAA or airlines or pilot unions, have mentioned this. What was the cause of MCAS activation? Did it activate for it's intended function, or because of some malfunction? Why have none of these pilots spoken out? Why has Boeing not said, "See, pilots can do this!"? Why hasn't someone else said, "See, it malfunctions all the time!"?

I would say, generously, that this is very unlikely to be true.

[Smythe]

The JATR final report:

https://www.faa.gov/news/media/attac...A_Oct_2019.pdf

[Flapsupbedsdown]

Originally Posted by GordonR_Cape

Off topic: The Mentour video is an attempt to emulate a runaway trim, since the B737 NG simulator is not programmed to do that! The crew inputs do not match a real world situation, but the idea is to show the out of balance forces on the stabiliser trim wheels. That is all...

If you want to show something then do it properly, that is only "propaganda"

[Bend alot]

Originally Posted by megan

We have an experienced aviator, Byron Bailey - ex military fighter & 777 & current biz jet, who writes a regular column in our local national paper (The Australian), and had this to say,Question, is what he's saying re MCAS activation cases in the US for real?

Ask The Australian if Mr Bailey can produce some evidence to support his claim - I am sure the FAA would love to know why they were not informed!

[Bend alot]

Originally Posted by Flapsupbedsdown

If you want to show something then do it properly, that is only "propaganda"

Propaganda has got EASA's attention and others re the 737 manual trim wheel in the NG and MAX, given that the simulators under state the force required to move the trim wheel does not help their concerns.

I would substitute "propaganda" with "evidence".

Not even the MAX simulators could simulate the MCAS fatal events - so it could only be done as a live drill.

[Grebe]

Originally Posted by Bend alot

Propaganda has got EASA's attention and others re the 737 manual trim wheel in the NG and MAX, given that the simulators under state the force required to move the trim wheel does not help their concerns.

I would substitute "propaganda" with "evidence".

Not even the MAX simulators could simulate the MCAS fatal events - so it could only be done as a live drill.

Interesting re simulators not having capability to duplicate stabilizer aero forces as a function of speed and elevator and stabilizer position

Over 40 years ago, used a heavy duty magnetic clutch - basically a magnetic disc/motor with metal particles in oil surrounded by a dc winding to evaluate torque versus speed for large drillmotors and getting a torque versus speed curve ( mostly linear ) and then a simple calc to get horsepower.

Thus, IMHO a relativively simple device could be used to duplicate aero loads as a simple computed function resulting from elevator position and stabilizer position and airspeed ( based on actual flight data ) and then tied to the trim wheel- cable system equivalent in the simulator. Drive it backwards is also possible. But of course it might cost a few thousand dollars per simiulator plus flight test data costs.

against a million $$ per plane cost for not doing it ??

By god we will save a million dollars no matter how many Billions and a few hundred lives it costs.