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737 MAX future

Old 11th May 2019, 09:06
  #61 (permalink)  
 
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Originally Posted by 737 Driver View Post
Based on historical experience, the MAX will be certified to fly again, there will be some initial public avoidance, but after a year (maybe less) most passengers will get over their qualms
I'm not flying in one.

And nobody has answered the following question (in any forum I've asked it): Are there any other unstable airliners out there which I may wish to avoid?
Gertrude the Wombat is offline  
Old 11th May 2019, 09:23
  #62 (permalink)  

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Originally Posted by Gertrude the Wombat View Post
I'm not flying in one.

And nobody has answered the following question (in any forum I've asked it): Are there any other unstable airliners out there which I may wish to avoid?
The words "unstable airliners" is meaningless. What do you mean by "unstable?"

Trying to guess your intent. In general terms every airliner is unstable at the limit. Push hard enough it will depart. However, at the edge of the envelope, it needs to be predictable. So to answer the question I think you are asking, is... Yes. All airliners are unstable. Avoid all airliners.
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Old 11th May 2019, 10:17
  #63 (permalink)  
 
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Originally Posted by PEI_3721 View Post
The modified MCAS - https://www.boeing.com/commercial/73...e-updates.page (17Apr - any later version) would only require two sensors to disable MCAS.
The acceptability of this depends the ease of flight for ‘abnormal conditions’ and the probability of occurrence. This should not be a problem, MCAS is only used in a small part of the flight envelope, not likely to be encountered often. However, given that previous 737s are sensitive to nose up pitch with high thrust - GA mode, then the acceptability of ‘abnormal’ flight in the 737 Max without MCAS might be more questionable.
Also consider the extent of the differences between the 737 Max and previous models - ‘it will be the same’, except for MCAS, etc. Are the normal flight handling qualities of the MAX sufficiently similar to previous aircraft - margin to certification limit - this is not the same judgement as ‘same type rating’.

The confidence in the modified design might be further questioned by the discovery of inoperative AoA Disagree elements in some aircraft. The effect of this depends on interpretation - either a simple pin program error (customer option), or a software error preventing the option from working, N.B. where - AoA Disagree is now a major aspect of the modification. https://finance.yahoo.com/news/boein...205151888.html (In the ‘continued’ section)

The objective of the modification is to prevent large trim changes which could reduce the ability to fly the aircraft. If this is not assured, then MCAS would require much higher integrity - flight with MCAS disabled is judged unacceptable, or the software has insufficient integrity.
Then the system might require three vanes or alternative means of cross checking / use of sensors. Such integration will take time and may involve complex certification assessment given the history of events.

Re preflight vane checks; the validity of electrical connections might be checked, but not the accuracy of the AoA value, which like an aircraft requires the vane to be ‘flying’.

Re stick shake; AoA for Vsw is an alerting function - cross check with triple speed display.
AoA for MCAS is high-order safety action function - system disabling, no alternative.

Yes but also needs to be noted is a issue known even with the NG and prior, is the ineffectiveness of the trim wheel under some conditions. actually "ineffective" is an understatement.

Does MCAS have or can have an effect on this well known manual trim deficiency?
Bend alot is offline  
Old 11th May 2019, 10:21
  #64 (permalink)  
 
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Originally Posted by Bend alot View Post
The aircraft is certified if an AoA fails the stick shaker goes off, possible a requirement to get certification - the aircraft still operates the same regardless of where you are in the envelope.

The difference is in the MAX you get more than the stick shaker with an AoA failure you get a change of aircraft characteristics in certain areas. That change is "unknown in quantity" close to a stall and that change is known to be outside certifiable limits.

I expect it is very easy to get certification with a MCAS U/S, but I very much doubt it can be done without detailed training best done in the simulator - so there is a reduced startle factor with less experienced pilots.

Keep in mind where MCAS is actually required is in a small window of variable conditions and to NEED to be there, it is probably not a walk in the park day. So best not to have more surprises and start learning along the way when workload is already high.

Example - above 1,000 ft flaps up AP on - Birds! pull up, AP disengages miss birds, Another flock of birds again pull up in MCAS area now and it trims. You then trim to level as birds seem gone (MCAS deactivated) yet another flock of birds - pull back, this time the coulomb just comes right back aft into your crouch just like a cable has broken. Startle factor for more than a fraction of a second and it is in a stall, at best a few thousand feet AGL.

So you have just done two avoidance's in a B737, then third was in a fighter jet. Best to have some fighter jet training if that is what can happen.
Even if the MCAS was disabled the STS would still be operational and this works to increase column force required in the event of a high pitch up at low speed.

once the MCAS is disabled any erroneous data can be eliminated using memory items followed by check lists for unreliable airspeed, AP off AT off F/D off pitch either 10-80% with flaps extended ( in this instance MCAS is not active anyway) or 4-75% clean, if MCAS has been disabled due to erroneous signals then at 4 degrees NUA and 75% you are going nowhere near the stall environment, moreover you are in control and not some sub system putting in NDA stab inputs, of course the system has to ensure controlled flight in all phases of flight, the only problem is that we know that at full column deflection the airflow load over the stab can exceed the electric or manual trim capability and Boeing recommends reducing these loads by momentarily releasing back or forward pressure and using the electrical or manual trim, not so easy to do this when you are hurtling towards the ground.

what we really need to know is why these aircraft had erroneous data in the first instance, was this a build fault, manufacturing fault, poor system maintainance, bird strike or other?

Ive been flying the Classic, NG & MAX since 2005 through to a week before it’s grounding and have never once needed to use the trim cut out switches, the MAX is a beautiful bit of kit to fly albeit with a now discovered fatal flaw.

Just how we rebuild passenger trust is going to be a real challenge especially if like us we have mixed fleet where we might be rostered an NG and then for operational requirements change to the MAX.

Even now given the publicity surrounding the MAX grounding we have a number of passengers on nearly every flight asking if this is a MAX, not helped by the fact that the briefing card says 737-8/ MAX, I think many people will either avoid airlines flying the 737 MAX or avoid Boeing aircraft, then of course every time there is an incident involving a 737 ( MAX or otherwise) the media spotlight will focus again on MCAS.

If i were Boeing I would be starting design on a clean sheet replacement for the 737 rather than the middle of the market replacement. I have total faith that Boeing will get this right? maybe continue with NG production along side the MAX giving customers an option at a heavily discounted price.

They are probably going to have to discount the MAX unit price in any event.
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Old 11th May 2019, 10:40
  #65 (permalink)  
 
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Cows,
‘… what else slipped through the regulatory net? ‘

Like the inability to recover the aircraft after a trim runaway - this is not changed by MCAS cutout - problem as per Bend alot #64. Reduced confidence in the procedure after the accidents and sim demo. The drill depending on pilot recognition and timely action, and a complicated ‘yo-yo’ manoeuvre.
This relates to an industry wide question of how much credit can be taken for human involvement in rare or surprising situations. Then the insolvable debate about training; those who can, those who can’t, and those who think they can, but do not perform at the critical time because the situation is not recognised or too difficult (where’s the ‘trim fail’ light).

Another ‘slip’ is the AoA display on EFIS. With AoA failure the gauge displays may not be removed, crews cannot determine which one is accurate - hazardous misleading information.
Also, why have a separate AoA display when the same information is shown overlaying the EFIS speed scale, that scale is associated with more meaningful dual cross-monitoring IAS (ADC) Disagree alert.
Unnecessary display clutter.
safetypee is offline  
Old 11th May 2019, 10:50
  #66 (permalink)  
 
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I have to say that if I got a stick shaker after takeoff, my first thought would not be «I have a faulty AOA sensor».
I would think stall and configuration. I would lower the nose to increase speed. Then start to find out what was going on.
And if my aircraft did not have the AOA disagree caution installed, AOA sensors may or may not be on my list of causes for the stick shaker. A SMYD failure would be more likely since I have never had a AOA failure on the NG in the 20 years I have been flying it. I don’t understand why it fails when it’s installed on the MAX?
This is a response to 737 Drivers claim that AOA sensor failure would be on the top of the list when a stick shaker goes off after takeoff.
ManaAdaSystem is offline  
Old 11th May 2019, 11:09
  #67 (permalink)  
 
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One pilot joins up just last month, and then makes over 200 posts, leaving no doubt
at all that he/she thinks the plane is fine and the pilots are not up to it.
One guess,,, which city this pilot is based! I wonder who his/her employer might be?
Was there talk that Russia used social media to influence an election? Could this be
a home grown equivalent?
Deepinsider is offline  
Old 11th May 2019, 11:11
  #68 (permalink)  
 
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EIFFS,
MCAS / STS, interesting points, and other aspects agreed
The ‘use’ of STS questions why it was not used in the first instance: - speculation, that the particular stability deficiency was AoA / manoeuvre related and thus not manageable with speed. Is STS applicable flaps up.
What more might this indicate about the extent of the aerodynamic problems, albeit in a small part of the flight envelope.

General question; does the Max have the two-stage (double press) TOGA selection, which is related to pitch attitude/rate; is GA /TOGA available with flaps up, and if without MCAS would the pitch-up be excessive (N.B. several incidents in NG).

Bend alot,
… ineffectiveness of the trim wheel under some conditions, actually "ineffective" is an understatement.
As noted by EIFFS, this is a serious problem to add to the recertification discussions.




PEI_3721 is offline  
Old 11th May 2019, 11:31
  #69 (permalink)  
 
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Originally Posted by Deepinsider View Post
One pilot joins up just last month, and then makes over 200 posts, leaving no doubt
at all that he/she thinks the plane is fine and the pilots are not up to it.
One guess,,, which city this pilot is based! I wonder who his/her employer might be?
Was there talk that Russia used social media to influence an election? Could this be
a home grown equivalent?
Well spotted!
marchino61 is offline  
Old 11th May 2019, 11:57
  #70 (permalink)  
 
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Originally Posted by Deepinsider View Post
One pilot joins up just last month, and then makes over 200 posts, leaving no doubt
at all that he/she thinks the plane is fine and the pilots are not up to it.
One guess,,, which city this pilot is based! I wonder who his/her employer might be?
Was there talk that Russia used social media to influence an election? Could this be
a home grown equivalent?
The tought has crossed my mind. He is also very well informed about all new developments and fixes.
ManaAdaSystem is offline  
Old 11th May 2019, 12:15
  #71 (permalink)  
 
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Chaps, let’s play the ball not the man.
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Old 11th May 2019, 12:18
  #72 (permalink)  
 
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Originally Posted by Bend alot View Post

MCAS has no redundancy, and if there is a failure of MCAS the flight characteristics do change in certain areas of the envelope. You just will not know how abruptly or placid this change might be until you find yourself there (that may never happen just like an engine failure after take-off) or even amount of change v/s speed. What is the difference in a turn? will it try roll you also?
MCAS/STS has two independent channels, so it does have redundancy. I think you may be referring to the fact that the loss of AOA will keep MCAS from activating. The loss of MCAS will not cause the aircraft to fall from the sky. Loss of MCAS will only change the handling characteristics approaching a stall. Most aircraft never, ever get near the stall regime in normal operations.
737 Driver is offline  
Old 11th May 2019, 12:25
  #73 (permalink)  
 
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Originally Posted by ManaAdaSystem View Post

This is a response to 737 Drivers claim that AOA sensor failure would be on the top of the list when a stick shaker goes off after takeoff.
Sorry if I gave that impression. This aspect was covered extensively in the other thread. What I said was if the stick shaker was going off and the aircraft was accelerating and climbing normally (i.e. obviously not stalling), then that would be a clear indication of an AOA issue.
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Old 11th May 2019, 12:29
  #74 (permalink)  
 
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Originally Posted by marchino61 View Post
Well spotted!
A few of us are around 200 posts - again!

Happens more on the rumours section than other areas.
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Old 11th May 2019, 12:29
  #75 (permalink)  
 
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Originally Posted by PEI_3721 View Post

General question; does the Max have the two-stage (double press) TOGA selection, which is related to pitch attitude/rate; is GA /TOGA available with flaps up, and if without MCAS would the pitch-up be excessive (N.B. several incidents in NG).
One press of the TOGA buttons will produce a 1000-2000 fpm rate of climb. A second press will advance the engines to full G/A power. MCAS only operates with the flaps retracted, so it would not be a factor during the initial G/A sequence (which is where one would have any issues with the power/pitch coupling).
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Old 11th May 2019, 12:30
  #76 (permalink)  
 
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except the man is playing all of us, and not the ball! He could declare his interest in all this, and state he has no relationship with big B of any kind..

G
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Old 11th May 2019, 12:31
  #77 (permalink)  
 
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Originally Posted by ManaAdaSystem View Post

The tought has crossed my mind. He is also very well informed about all new developments and fixes.
Well, I do actually fly this aircraft ........ Guilty as charged!
737 Driver is offline  
Old 11th May 2019, 12:32
  #78 (permalink)  
 
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Originally Posted by groundbum View Post
except the man is playing all of us, and not the ball! He could declare his interest in all this, and state he has no relationship with big B of any kind..
Okay folks, getting a little paranoid here, but no I do not have any relationship with Boeing except for the facts that I have flown their aircraft for over 30 years. That should take care of any concerns, right?
737 Driver is offline  
Old 11th May 2019, 12:34
  #79 (permalink)  
 
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Originally Posted by 737 Driver View Post
MCAS/STS has two independent channels, so it does have redundancy. I think you may be referring to the fact that the loss of AOA will keep MCAS from activating. The loss of MCAS will not cause the aircraft to fall from the sky. Loss of MCAS will only change the handling characteristics approaching a stall. Most aircraft never, ever get near the stall regime in normal operations.
Yep, all redundancy except till the AoA's then a single point failure. So is there no need for you to know the change in handling even if it is severe?
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Old 11th May 2019, 13:46
  #80 (permalink)  
 
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737 Max MCAS recertification and return to service

The preceding thread on 737 Max future has been closed, presumably due to inappropriate posts - play the ball, not the person.
Closure appears to be an excessive reaction to a problem which could be managed by other means; as a result the interesting theme being discussed - 737 Max future, return to service, recertification, has been stifled.
Thus, in continuation: ‘737 Max MCAS recertification and return to service’.

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