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MAXís Return Delayed by FAA Reevaluation of 737 Safety Procedures

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MAXís Return Delayed by FAA Reevaluation of 737 Safety Procedures

Old 2nd Dec 2019, 14:21
  #4221 (permalink)  
 
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Originally Posted by OldnGrounded View Post
In secret.
Which must be diagnosed as runaway trim after 3 seconds EXCEPT when it is operating in certain corners of the flight envelope

Which are secret
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Old 2nd Dec 2019, 15:25
  #4222 (permalink)  
 
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Originally Posted by Maninthebar View Post
Which must be diagnosed as runaway trim after 3 seconds EXCEPT when it is operating in certain corners of the flight envelope

Which are secret
There is no definition for "runaway trim" so it is impossible to diagnose it.

What is clear is that if one determines "runaway" as continuously operating, then any such motion will stop at the full-stops, which stops the runaway; ergo, the trim can not, in fact, runaway. No matter what, it will actually stop.

Were I writing manuals I would not use that term, but instead use "undesired trim movement that adversely affects pitch control forces."

Three seconds is not a requirement, but an expectation. The full fatal dose of MCAS nose-down trim is up to 27 seconds of trim run time, 9 seconds at a time. At higher speed the fatal operating time appears to be closer to 12 to 15 seconds (ET302 was nearly 18 seconds in total; 9 + 6 + 3.)

What is missing from the documentation is the pitch control force required to hold level flight and what amount of force should be an indicator to re-trim the plane. It's clear for the ET302 flight that nearly -3 units off of nominal trim did not generate such large forces as to cause the PF to trim that out before cutting out the trim motors. The first manual trim input to counter MCAS did not happen until -5 units delta had been reached and that was after 15 seconds of MCAS AND trim, though only 2 units were offset. However, that remaining -3 units of trim offset would cause the AND force to increase as the speed increased.

I've seen no documentation of expected control forces at any point in either crash flight. .
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Old 2nd Dec 2019, 15:39
  #4223 (permalink)  

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Tex Johnson, in a demonstration flight for Boeing, flew a barrel roll. in a 707. It's probably mentioned in his autobiography "Tex Johnston: Jet Test Pilot". There are a couple of youtube video's of it.
I was watching them yesterday; around the same time a European airline training captain was allegedly regularly doing the same on training flights.

As the Boeing boss said to Tex ďyou know itís safe, I know itís safe but donít do it againĒ.

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Old 2nd Dec 2019, 22:06
  #4224 (permalink)  
 
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Originally Posted by golfyankeesierra View Post
and it isnít referenced to pitch angle either
It certainly can be., if you define it that way.

On aircraft with a fuselage mounted AOA sensor, it makes sense to use the fuselage as the reference, not some hypothetical wing chordline. Which is moving around and varies along the span as well.

The AOA definition used for 2D sections isn't very transferable to a full aircraft.
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Old 2nd Dec 2019, 22:39
  #4225 (permalink)  
 
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Originally Posted by Mad (Flt) Scientist View Post
It certainly can be., if you define it that way.

On aircraft with a fuselage mounted AOA sensor, it makes sense to use the fuselage as the reference, not some hypothetical wing chordline. Which is moving around and varies along the span as well.

The AOA definition used for 2D sections isn't very transferable to a full aircraft.
I agree, the presence of wing twist and variation in section to account for spanwise flow changes makes wing sections a less desirable reference on an aircraft.

Pitch is still not AoA even if referenced to the fuselage because AoA includes both vertical and horizontal oncoming relative wind components. An aircraft operating at a certain pitch can have differing AoA readings from horizontal to climbing to descending flight. A plane may remain in a stall at 25 degrees pitch and, as horizontal airspeed bleeds off, convert from 25 degrees AoA to the unfortunate nearly 90 degree AoA.
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Old 2nd Dec 2019, 23:02
  #4226 (permalink)  
 
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AoA: "the difference between where a wing is pointing and where it is going"
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Old 2nd Dec 2019, 23:28
  #4227 (permalink)  
 
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Originally Posted by MechEngr View Post
There is no definition for "runaway trim" so it is impossible to diagnose it.

What is clear is that if one determines "runaway" as continuously operating, then any such motion will stop at the full-stops, which stops the runaway; ergo, the trim can not, in fact, runaway. No matter what, it will actually stop.

Were I writing manuals I would not use that term, but instead use "undesired trim movement that adversely affects pitch control forces."

Three seconds is not a requirement, but an expectation. The full fatal dose of MCAS nose-down trim is up to 27 seconds of trim run time, 9 seconds at a time. At higher speed the fatal operating time appears to be closer to 12 to 15 seconds (ET302 was nearly 18 seconds in total; 9 + 6 + 3.)

What is missing from the documentation is the pitch control force required to hold level flight and what amount of force should be an indicator to re-trim the plane. It's clear for the ET302 flight that nearly -3 units off of nominal trim did not generate such large forces as to cause the PF to trim that out before cutting out the trim motors. The first manual trim input to counter MCAS did not happen until -5 units delta had been reached and that was after 15 seconds of MCAS AND trim, though only 2 units were offset. However, that remaining -3 units of trim offset would cause the AND force to increase as the speed increased.

I've seen no documentation of expected control forces at any point in either crash flight. .
It did not take 18 seconds for the ET302 crew to recognize the erroneous nose-down trim and respond. Nor was the time to recognize and begin to respond "fatal."

The first MCAS nose-down trim started at 05:40:00 and lasted (uninterrupted) for 9 seconds. It moved trim down 2.5 units from 4.6 to 2.1. The crew responded with nose-up trim at 05:40:12, three seconds after the AND stopped and 12 seconds after it first activated. They trimmed up, but only from 2.1 to 2.4.

The second MCAS nose-down trim started at 05:40:20 (5 seconds after the crew released the MET switch). It trimmed down for about 8 seconds from 2.4 to 0.4 before it was interrupted. The crew trimmed up for close to 9 seconds to 2.3. They then shut off electric trim.

They recognized that erroneous automatic trim had placed the plane in an out-of-trim condition. What was fatal was that they didn't trim back up closer to 4.6 before shutting off electric trim and then made the same mistake after turning it back on.

The time for either Lion Air Captain to recognize and respond to erroneous AND trim was not "fatal" either. The Lion Air report indicates that, on the flight before the accident flight, the crew allowed MCAS to run for the full 9 seconds (or nearly so) 3 times. None of those were "fatal" because the crew trimmed back up to 5-6 units each time. On the accident flight, the first MCAS activation (at 23:25:17) only lasted for 2 seconds before it was recognized and interrupted by the Captain trimming up (the Captain interrupted MCAS with nose-up MET 21 times and never allowed the AND command to run the full 9 seconds). The FO, on the other hand, allowed MCAS to run for the full 9 seconds (or nearly so) twice. He recognized there was a trim problem after the first MCAS activation but only trimmed up by an insignificant amount.

Last edited by Notanatp; 3rd Dec 2019 at 00:04.
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Old 2nd Dec 2019, 23:29
  #4228 (permalink)  
 
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It seems a french test pilot, Jean Franchi and then a british one Brian Walpole both both barrel rolled a Concorde during testing. From the pilot video below it's clear the french were quite familiar with this trick and eager to show their friends across the channel how it was done.

I've heard it said that this is a positive G manoeuver, and can be done with any aircraft, whether that is true I don't know because I don't pilot.

Concorde barrel rolls.

There is a rumor that it was also done during a retirement flight.

Edmund
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Old 3rd Dec 2019, 16:44
  #4229 (permalink)  
 
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A decision soon; or softening up for bad news.

https://www-cnbc-com.cdn.ampproject....offensive.html
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Old 3rd Dec 2019, 17:06
  #4230 (permalink)  
 
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Salute!

Interesting, Safety
I hope they have line pilots at the gala event. don't you? Maybe even a hop in the bird to show what MCAS activation feels like, as well as high AoA without MCAS.

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Old 3rd Dec 2019, 18:48
  #4231 (permalink)  
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India weighs tougher rules for MAX

India weighs tougher rules for Boeing 737 MAX on return to flying: source


By Aditi Shah

MUMBAI (Reuters) - India is considering setting an experience threshold for pilots who fly Boeing's <BA.N> 737 MAX planes, as it moves to ensure safety once the aircraft returns to service, a senior official of the air safety regulator told Reuters.

The 737 MAX, the fastest-selling plane in the history of Boeing, has been grounded worldwide since March, after 346 people were killed in two crashes in five months.

Boeing is making software changes, readying a new pilot training plan and must run a key certification test flight to get approval from the U.S. regulator, the Federal Aviation Administration (FAA), before the planes can resume flying.

India's Directorate General of Civil Aviation (DGCA) may consider mandating a minimum number of flying hours for pilots of the 737 MAX, the source said, adding a decision would be made once it is clear when the planes are fit to return to the air.

"Pilot training is a serious matter for the DGCA and the airlines will also need to work on building pilot confidence," said the source, who sought anonymity, as the discussions were private.

The regulator will also make it mandatory for Boeing to set up simulators in India and for airlines to carry out comprehensive pilot training before it allows the planes to start flying, the source added.

Reuters could not immediately reach the DGCA to seek comment.

In a statement, Boeing said it was working closely with global regulators on a training program to help enhance pilots' understanding of the updated 737 MAX flight control systems.

"Boeing will continue its commitment to developing training that supports safe, efficient operations and meets regulatory requirements," it said in the emailed statement.

India's DGCA is one of several regulators that have indicated they will perform independent inspections of the grounded planes once the U.S. FAA clears them to fly.

Indian carrier SpiceJet <SPJT.BO> has about a dozen Boeing 737 MAX planes in its fleet and 155 on order - among the largest single orders for the narrow-body plane.

Boeing had delivered close to 400 of the 737 MAX globally before the March grounding, and it has nearly 5,000 orders for the aircraft, a more fuel-efficient version of its best-selling single-aisle 737 series.
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Old 3rd Dec 2019, 19:09
  #4232 (permalink)  
 
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Salute!

India's actions seem rather harsh and maybe even unnecessary.
In all fairness, Boeing's AD after the Lion crash recommending turning off the trim works if you do it at the onset of the MCAS trim or after re-trimming and then turning off the trim.
The problem was not knowing the system was installed, how it was supposed to work, and then recognizing its activation. Good friggin' grief. The previous Lion flight crew survived even tho they did not know that MCAS was the problem. The ET folks waited too long and did not keep their speed down to normal climb schedule. Seems they had not been briefed that the wheel trim switches worked per pervious models and defeated the MCAS.
I personally would have no problem with jumping into one of the jets a year ago, with all its warts and all, if I knew the MCAS was installed and how it worked and having a simple light on the fault panel that said "MCAS" when the system was activated. Wouldn't you?
I am not going along with all the "just fly the plane" arguments from a year ago. Sheesh. I did just fine with several problems that you discover in new planes and have to innovate. But I never encountered one due to a system that could drastically influence my flight controls and was not briefed in academics or from another crew.

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Old 3rd Dec 2019, 19:22
  #4233 (permalink)  
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Originally Posted by gums View Post
Salute!

India's actions seem rather harsh and maybe even unnecessary.
I think what we're seeing -- and not just from India -- is that both Boeing and the FAA have lost the trust of much of the world -- and other CAAs aren't willing to take the risk of accepting those organizations' judgments and decisions without being seen to do their own verification. Even regulators who privately accept that Boeing/FAA are doing the right thing with the MCAS fix are going to be reluctant to let their public see them as rubber-stamping the work of the Americans.

I personally would have no problem with jumping into one of the jets a year ago, with all its warts and all, if I knew the MCAS was installed and how it worked and having a simple light on the fault panel that said "MCAS" when the system was activated.
I think most here would probably agree with that, although it might also be nice to hear about the pitch-up characteristics of the bare airframe in various parts of the envelope.

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Old 3rd Dec 2019, 20:52
  #4234 (permalink)  
 
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Salute!

Agreed, Old.... lottsa trust gaining on heah, ya think?

The comment about pitch up potential has merit, and I remain to be convinced that MCAS was simply a kludge to keep control force vs AoA gradient within requirements. Most folks associate pitch up problems with T-tails, but that ain't always the case. Ask PEI, our resident test pilot. The stick shaker is not anti-stall aerodynamics, but MCAS is close to an anti-stall feature. I flew two that had actual flight control limits to stay outta trouble, although the Voodoo gave plenty of warning when subsonic. The Voodoo "manual command signal limiter" worked when autopilot was not used, and it took over 60 pounds to overcome. Sounds like the 737 control column switches that overcome the A/P or STS or..... So I could keep pulling even tho HAL was telling me not to.

Oh well, just some thots from an old aviator.

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Old 3rd Dec 2019, 21:28
  #4235 (permalink)  
 
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Boeing has invested a lot into the storyline that the two crashes were entirely the fault of inexperienced and poorly trained pilots, so India's response is logical. Boeing can't have it both ways. Either the plane as designed can be safely flown by the (relatively) low hour pilots hired by the low cost airlines that they sell it to, and the crash was the result of a technical defect -- or the plane was technically fine and the pilots who were trained to international standards were deficient. If the latter, then the standards for flying the plane have to be changed, lest we watch more of them hit the ground unexpectedly.
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Old 3rd Dec 2019, 21:49
  #4236 (permalink)  
 
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Gums

You are on to a big problem here.
If the Max is approved with a modified MCAS there is the possibility that someone enter a high AOA with flaps up and the MCAS works as intended.
Lets say on a climbing and turning departure, just for arguments sake!

The MCAS operates with full speed when flaps up, something a 737 pilot is only used to with flaps extended.
There is a remote chance a pilot could pull against it, and as that does not work, trim against MCAS.
As I understand it he is now entering a lighter stick with higher AOA and I can see this ending up with a stall and a spin in an extreme case.

Looking forward to my next sim, as I intend to test this if time permits.

Cheers
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Old 3rd Dec 2019, 21:56
  #4237 (permalink)  
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Originally Posted by LetItBeDone View Post
There is a remote chance a pilot could pull against it, and as that does not work . . .
I think that MCAS 2.0, as so far described, no longer disables the column cutout switches -- which may be relevant to your point, if I I understand it correctly.

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Old 3rd Dec 2019, 22:29
  #4238 (permalink)  
 
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Yo gums, et al.
The emerging views requiring more experience (and training) could relate to the pitch trim operation and ability to detect a trim runaway other than MCAS inhibit; which could also apply to the 737 NG.

The investigation into the Flydubai 737 accident, this forum, elicited the following information from Boeing: - the disclosure of opinion and assumption about pilots experience.
This relates to relatively inexperienced crews - perhaps more prevalent in modern times, the balance of flying P1 / P2 before obtain a command, and significantly that a new 737 Captain could have most prior experience on FBW aircraft - Boeing or Airbus.
Thus current crew experience of manual trim operation could be compared with that pre 707.

Upon the request of the investigation team the aircraft manufacturer, the Boeing Company, responded that the Boeing 737 aircraft documentation does not contain the specific guidance on the general principles of the forces trim. Boeing is of the opinion that the indicated skills are integral of the basic airmanship to perform flights on large transport aircraft. At the same time the manufacturer notes that this documentation is designed based on the assumption that the customers have had the previous flying experience on the jet multi-engine aircraft and are familiar with the basic systems of the jet aircraft and basic flight maneuvers, common for the aircraft of the type. In relation to this FCTM does not incorporate the background information, of which the awareness is considered as prerequisite to familiarize with the concerned document.

Note: Ö at the movable stabilizer introduction into service Boeing has issued the detailed guidance, explaining the general principles of the use of such systems through the Boeing 707 and 720 aircraft. These materials can be found in the Boeing Airliner magazines of April, 1959 and May, 1961 Ö
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Old 3rd Dec 2019, 22:36
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Salute!

Well, Let it, if all the pilots knew about a new system and how it worked and under what conditions, then we prolly would not have lost over 300 souls. We prolly would not have to have sim training or anything else, although I personally would liked to have seen the "with and without" MCAS flight dynamics. You know. Some times the caution lights are not enough.

As of now, I do not believe any 737 sim can turn off MCAS so you can "feel" what the hell it was supposed to "augment". GASP! The whole damned system and its implemantaiton and secrecy and such infuriates me. If I were in the high purple in ALPA or carrier unions I would be a cable news star from day one after discovering MCAS was implemented on my plane.

Gotta back off here, so excuse me a bit.

Gums sends....
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Old 3rd Dec 2019, 22:51
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Salute!

Thanks, PEI.

I was surprised 20 or 30 years ago to find out that many of the heavies moved the stab for trim versus the elevator. Found out after a student of mine pranged at Little Rock and lottsa the CVR had the noise of the trim jackscrew. Then the Air Alaska tragedy.

When I was a yute, fooling around with the horizontal stab was not a great idea, but I knew one good pilot that adjusted the thing on his Yankee to reduce the drag.

My conviction is that there is more of an aero problem with the MAX than we are being told.

Lastly, I do not feel that one must have thousands of hours to safely fly the 737 with or without MCAS ( mainly without, heh he ). The decision to market the plane and claim that no training was required was bad enough. But implementing a screwed up system and not telling the pilots bordered on criminal.

Gums sends...
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