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

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

Old 14th Jun 2019, 02:50
  #401 (permalink)  

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That graph is completely insulting to any professional logic. If ever you need an illustration for the old adage about lies and statistic, this is as bad as it gets.

What a strange metrics, hull loss per type. Heck, burned toasts per house windows?

... CFIT, LOC-I, terrorism - including military,.... it must be a quick satisfying job to produce an impressive colourful piece without putting any work into it.
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Old 14th Jun 2019, 02:54
  #402 (permalink)  
 
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See:
https://en.wikipedia.org/wiki/Ethiop...nes_Flight_409
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Old 14th Jun 2019, 04:04
  #403 (permalink)  
 
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Originally Posted by FlightDetent View Post
That graph is completely insulting to any professional logic. If ever you need an illustration for the old adage about lies and statistic, this is as bad as it gets.

What a strange metrics, hull loss per type. Heck, burned toasts per house windows?
On the contrary, hull loss per (million) departures, grouped by type, is a long standing metric tracked in the industry.

In fact Boeing's Aviation Safety group has been updating and publishing the above chart every year for at least 20 years!

Originally Posted by infrequentflyer789
Updating the chart to add the MAX
This might not be statistically valid since the MAX doesn't have enough departures (<< 1 million) relative to the other data points.
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Old 14th Jun 2019, 04:16
  #404 (permalink)  

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Originally Posted by futurama View Post
On the contrary, hull loss per (million) departures, grouped by type, is a long standing metric tracked in the industry. In fact Boeing has been updating the above chart every year for at least 20 years!
Only as long as they come at the winning end of it. It is completely meaning less. How do these add in
- military shoot downs
- hijack crashes
- midair collisions caused by the other involved ac
- maintenance losses

As the hull losses - heaven and all hard working people sent - become a scarce occurrence, the outlier events distort any purpose it may have had. And I suggest it never did. It is a PR stunt for the Instagram generation, oh wait..


​​​​
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Old 14th Jun 2019, 04:33
  #405 (permalink)  
 
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Originally Posted by FlightDetent View Post
Only as long as they come at the winning end of it. It is completely meaning less. How do these add in
- military shoot downs
- hijack crashes
- midair collisions caused by the other involved ac
- maintenance losses
​​​​
Um, the chart title in big bold type spells "Accident Rates by Airplane Type". Most of the items you list above (except midair collisions) are not considered accidents by ICAO definition, and therefore excluded. For statistical purposes, midair collisions are commonly included as separate events.

Boeing has been publishing variants of this data since 1959 (and as I mentioned, in the present form for at least 20 years). I wasn't aware that Instagram pre-dated the moon landing.
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Old 14th Jun 2019, 08:02
  #406 (permalink)  
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Originally Posted by GlobalNav View Post
I'm m

How can you be sure the standards are inadequate? I think it’s more likely the process of delegation and signing off on compliance. If exiting standards had been complied with, this would not have happened.

Item 1. 25.255 requires a maximum demonstrated out of trim of 3 seconds at applicable trim rate, that then will provide controllability for the pilot to manage the pitch to be able to pull 1.5 g with no more than a normal short term limit of force applied by a single pilot. The MCAS exceeded the trim rate applicable so that misses the target, available pitch to achieve g was not available, and it appears the force applied comes from two pilots, in excess of the single pilot short term force...

Item 2. Whatever it is called, MCAS was a SAS system, and the consequences from a failure of any SAS system, as well as the warning/alert seem to be way off the mark IMHO.25. 672


If pitch control is inconsequential then there is no problem. The smoking hole in the ground suggests that is not the case.



NB: my reservations on the compliance of the design does not mean the design cannot be acceptable, all applicants in a PSCP may propose an ELS to meet the requirements of certification. In this csse, that would need to have considerable safety training or additional system architecture to be reasonable.

​​​​​​Out of trim is a global issue for systems with manual trim as the reversionary mode. That is not just the Max, or NG.

The Max happened to introduce a new vector towards pain. The earlier designs are less likely to get so far into the rough but they can and then they all have the same handling issue. Adding a high torque backup would be a major undertaking, but that is what exists on many Boeing like the 777, 747betc. The Airbus has a manual trim backup.... But that the control of the hydraulic motors of the THS.Lose both hyd sys and no THS changes possible.




​​

Last edited by fdr; 14th Jun 2019 at 08:35.
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Old 14th Jun 2019, 09:03
  #407 (permalink)  
 
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fdr # 398
Yes getting close, but two related issues divide our views.

First, ‘… the technique to unload the trim to gain in trim condition again is able to be taught’ assumes that there will be sufficient control to achieve this, and also time, altitude, etc, in which to recover. A solvable technical issue involving many factors, variables, difficult to bound, apart from the flight test risks in proof.

Second ‘… however with training the recovery would be achievable’, continues the assumption that pilots can be taught to remember, recall, and correctly act in a rare, never expected to be seen situation (cf Wind-shear, CFIT accidents, and both with alerting). Actions are easier to teach than ensuring a consistent and correct identification of the situation - knowhow is not the same as know when. A human issue, which cannot be bounded or assured with any equivalence of a technical system.

Human performance can be deficient with respect to a situation, will the industry accept this risk in the specific situation with potential fatal outcome.

[for those who wish to counter argue with ‘failing to flare’ during landing, consider the likely outcome vs aircraft strength requirements (technical), and training and repeated exposure to the situation (human).]


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Old 14th Jun 2019, 09:13
  #408 (permalink)  
 
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Originally Posted by fdr View Post
Item 1. 25.255 requires a maximum demonstrated out of trim of 3 seconds at applicable trim rate, that then will provide controllability for the pilot to manage the pitch to be able to pull 1.5 g with no more than a normal short term limit of force applied by a single pilot. The MCAS exceeded the trim rate applicable so that misses the target, available pitch to achieve g was not available, and it appears the force applied comes from two pilots, in excess of the single pilot short term force...

Item 2. Whatever it is called, MCAS was a SAS system, and the consequences from a failure of any SAS system, as well as the warning/alert seem to be way off the mark IMHO.25. 672


If pitch control is inconsequential then there is no problem. The smoking hole in the ground suggests that is not the case.


​​
FDR you have totally misinterpreted the reason for the requirement contained in FAR25.255.
This standard was developed to address the "jet upset" problems experienced in the early days of jet transports.
The problem was seen as either insufficient elevator power, or stabilizer jack stalling as a result of deliberately or inadvertently applied longitudinal trim.
The regulation required that a defined level of stability and control was available if the mis-trim was:
1. 3 seconds at the no load trim rate;
2. 30 lbf stick force for manual trim:
3. The maximum trim which could be applied by the autopilot before it disconnected due to overload.
Each FAR standard is written as a stand alone requirement, you cannot try to apply a requirement written about mis-trimming to an event which is clearly about a control runaway.
The appropriate paragraphs for B737 stabilizer malfunctions are 25.671, 672 and 677.
Unless you are experienced in interpreting these requirements you may have difficulty working out what is really required.
Please don't forget to read the appropriate AC's as well.
It may also be helpful to read the equivalent paras of FAR 23 and AC 23-8.
I know these are for light aircraft but the guidance material about runaways is more comprehensive, it may give you an idea of how the FARs may be interpreted.
They will also give you some information about control open loop/closed loop recognition delay times used for malfunctions/runaways
You have next to no chance of working out what was required for certification or what tests were made without, copies of all certification meeting minutes, the agreed means of demonstrating compliance and the compliance reports for each FAR standard.
Unfortunately the FAR certification standards, as written, can be just the beginning of a long and complex path before all parties actually agree to the test required and the results expected.

Last edited by zzuf; 14th Jun 2019 at 09:57.
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Old 14th Jun 2019, 09:57
  #409 (permalink)  
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Originally Posted by yoko1 View Post
BTW, there if no "if" about the g-forces. They are included in the published FDR data. The aircraft registered nearly negative 2 g's near the end of the flight. If the pilots had not been strapped in, they surely would have hit the ceiling. At a minimum, the Captain lost some leverage against the yoke as he was attempting to pull back.

You have to keep in mind that in this flight region beyond Vmo, the aircraft would be reacting very differently than normal to control inputs. There were already plenty of signs that the ET302 Captain was not particularly comfortable with hand flying, and that was with an aircraft within the flight envelope. If you've ever been an instructor pilot and seen a student pilot make very tentative control inputs because they are nervous about what will happen, then that's the closest example I could give of why the Captain was not more assertive with making the necessary trim adjustments.

The recorded g is measured at a station near the mid section of the wing. Under either negative or positive accelerations other than 1g, the flightdeck load experienced can be much greater in either sense than recorded. Conventional simulators are limited in achieving the forces experienced under pitching conditions. Where the pitching rate is high, the difference can be noticeable. The vibration at the cockpit can be very noticeable as well, it may be low amplitude but can uncage your eyeballs.

At high MACH there is a tendency to a pitch down coming from the development of normal shock on the underside of the wing.which reduces lift, and that results in a flightpath that tends to reduce towards a ballistic path. case is odd, the lift being reduced. The pitch trim case mitigates the pitch change to an extent but the nose still lowers unless AoA is increased to recover CL. The Cp doesn't move much, the moment reduces but the flightpath degrades, lift is greatly reduced for a given AoA. Increasing pitch gets towards buffet boundary, but increase in AoA reduces the lower normal shock.. If you are closed loop, the crew notice an increase in backforce to maintain level flight, but if you are open loop or at a control limit, then the nose will drop until MACH number starts to reduce with increasing temperature. Both of these cases however did not get into compressibility issues, these effects occur well beyond MMO, but are noticeable before Md.

If the above doesn't gel with AP3456A, or AFNA etc, I was surprised by the hi res DES/LES 3D study of the wing. I expected to see a Cp shift rearwards, was not expecting a collapse of CL. Where stab and elevator maintain the authority to increase AoA, the effect is not overly dramatic. If you are open loop, it is much more eventful.

Enough of that.

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Old 14th Jun 2019, 10:52
  #410 (permalink)  

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Originally Posted by futurama View Post
Um, the chart title in big bold type spells "Accident Rates by Airplane Type". Most of the items you list above (except midair collisions) are not considered accidents by ICAO definition, and therefore excluded. For statistical purposes, midair collisions are commonly included as separate events.

Boeing has been publishing variants of this data since 1959 (and as I mentioned, in the present form for at least 20 years). I wasn't aware that Instagram pre-dated the moon landing.
It did not, exactly my point.The whole thing is barnumesque (mid 1800's) irrespective of audience.

It implies there is causal connection between aircraft models (not types, and still dubiously applied) and hull loss accidents.

If you do the little work and sort the graph by rate and not EIS, the message buy modern, buy Boeing screams out. Both understandable conclusions. Without these being possible, the chart would had not existed.

​​​​​​Surely there must be robust methodology and properly validated inputs behind. But the message is void and I cannot see what is the expertise field inside aviaiton industry where such comparison makes any meaningful sense. Sales? Definitely. Ops? Nada.

Let's see the updated one with T7 and Max events. For the latter, there is already two tragic data points too many. Though it might well be discontinued claiming possible errors in interpretation due to different operating theatres, human error being the key reason of mishaps anyway and similar.
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Old 14th Jun 2019, 12:31
  #411 (permalink)  
 
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there's a theme running through a lot of the posts and media postings that I'd like to counteract. The theme is this was an unforseen situation or a unique failure point or something never seen before or a multitude of little issues adding up or a complex engineering/HF scenario etc.

IT'S NOT. It's a basic basic basic engineering flaw to build a system that controls a flight surface based on a single input. Boeing is proud to have years and years of engineering heritage so it knows full well the design was flawed and cheap even as soon as the first person said "we could get away with just 1 input". 100 other engineers would have immediately said no way not ever. But obviously somewhere a commercial person stepped hard enough on the Engineers to get the single input design commissioned. Everything else is just collateral damage. I can even understand though not like the decision to have a primary control surface move just to send feedback back to the stick, rather than add a servo to do the job. All the bits were there so it was too tempting to add some lines of code and voila!

G
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Old 14th Jun 2019, 15:56
  #412 (permalink)  
 
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Too tempting...

Originally Posted by groundbum View Post
there's a theme running through a lot of the posts and media postings that I'd like to counteract. The theme is this was an unforseen situation or a unique failure point or something never seen before or a multitude of little issues adding up or a complex engineering/HF scenario etc.

IT'S NOT. It's a basic basic basic engineering flaw to build a system that controls a flight surface based on a single input. Boeing is proud to have years and years of engineering heritage so it knows full well the design was flawed and cheap even as soon as the first person said "we could get away with just 1 input". 100 other engineers would have immediately said no way not ever. But obviously somewhere a commercial person stepped hard enough on the Engineers to get the single input design commissioned. Everything else is just collateral damage. I can even understand though not like the decision to have a primary control surface move just to send feedback back to the stick, rather than add a servo to do the job. All the bits were there so it was too tempting to add some lines of code and voila!

G
It was more than tempting - it was just a little add on to the speed trim system in the eyes of B. The fact that the speed trim system itself has been accepted by all involved in 737 ops (I have to say I found it a strange bit of kit when training on the -300 quite late in career) makes the mod even more tempting.
Doesn’t make it right though - and doesn’t make the STS right either.
B have used this method on other aircraft too to achieve various aims (tanker trim for example) so it is a deep rooted solution in the company. It does however grab the aircraft by the balls and all you need then is a Speedy Gonzales coming along to misuse the situation.
I still think it would be worthwhile to replace this feature completely by a direct feel input for all the reasons outlined already - even if the delay/costs are awful - at the end you get an honest aeroplane to sell the customers.
PS for those who don’t know, having grabbed hold of the aforementioned Saturday night equipment Speedy Gonzales then says “May I trouble you for your wallet?”

Last edited by bill fly; 14th Jun 2019 at 21:16. Reason: PS
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Old 14th Jun 2019, 23:09
  #413 (permalink)  
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Is it possible to make a good MAX? Things it would need, in of course, my humble opinion.

Obviate the need for MCAS entirely. The well proven STS? Experienced pilots give feedback as to it being really necessary. Take Occam's razor to anything that inputs to that 47 feet of ultimately powerful flying surface.

The manual trim system is frighteningly disappointing if its design goal is defeated so easily. The number of turns is already high, so you can't have a higher ratio. Is it conceivable that the stabilizer could be hinged forward of the centre of rotation? That would require one heck of a beam to the jackscrew but I'd hazard a guess that it could be contained within the tail profile.

Just think how many problems would go away if that could be implemented. (I know, it's too obvious for there not to be a reason for the way it is, though I'm darned if I can understand the original thinking.) For the system to be meaningful, I'd want to see crews hand flying while using it - right down to the flare. Needles to say, there would have to be almost perfect simulation - which I suggest would be a first for this task.

Whatever the decision, a long hard look at elevator authority. Thinking back 50 years, the BAC 1-11 had a switch that threw away the Q-Feel and gave an electric trim at a fixed 180kts. With care, it worked very well and was a very comforting backup.

A third AoA vane? There is enough varied data for a black box to give more than just a comparison fail warning. A very realistic 'most likely side' fail would be achievable.

Okay, you do all this and what have you got? Experienced forum members seem to like the aircraft, but my old bones itch when I see that ground clearance . . . or lack of it. We've discussed putting a tad of wing down in the past (following a very curly landing) and I was surprised that a few admitted to doing just that. I assume the MAX requires a very flat kick-off on X-wind landings. Fine for the experienced types, but what about the 'Children' who are gaining their first real experience of difficult weather while on line. Is this aircraft as critical to land as would appear? It seems to me to be a costly piece of kit for a crew still having to display P and L plates.
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Old 14th Jun 2019, 23:25
  #414 (permalink)  
 
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Originally Posted by Loose rivets View Post
Is it conceivable that the stabilizer could be hinged forward of the centre of rotation?
I'm struggling to understand what that actually means. Can you elaborate ?

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Old 15th Jun 2019, 01:04
  #415 (permalink)  
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Originally Posted by zzuf View Post
FDR you have totally misinterpreted the reason for the requirement contained in FAR25.255.
This standard was developed to address the "jet upset" problems experienced in the early days of jet transports.
The problem was seen as either insufficient elevator power, or stabilizer jack stalling as a result of deliberately or inadvertently applied longitudinal trim.
The regulation required that a defined level of stability and control was available if the mis-trim was:
1. 3 seconds at the no load trim rate;
2. 30 lbf stick force for manual trim:
3. The maximum trim which could be applied by the autopilot before it disconnected due to overload.
Each FAR standard is written as a stand alone requirement, you cannot try to apply a requirement written about mis-trimming to an event which is clearly about a control runaway.
The appropriate paragraphs for B737 stabilizer malfunctions are 25.671, 672 and 677.
Unless you are experienced in interpreting these requirements you may have difficulty working out what is really required.
Please don't forget to read the appropriate AC's as well.
It may also be helpful to read the equivalent paras of FAR 23 and AC 23-8.
I know these are for light aircraft but the guidance material about runaways is more comprehensive, it may give you an idea of how the FARs may be interpreted.
They will also give you some information about control open loop/closed loop recognition delay times used for malfunctions/runaways
You have next to no chance of working out what was required for certification or what tests were made without, copies of all certification meeting minutes, the agreed means of demonstrating compliance and the compliance reports for each FAR standard.
Unfortunately the FAR certification standards, as written, can be just the beginning of a long and complex path before all parties actually agree to the test required and the results expected.
AC25.07D covers the background for 25.255, however the B737 is an aircraft with a powered trim system ergo "it must be possible from an overspeed condition at VDF/MDF to produce at least 1.5 g for recovery by applying not more than 125 pounds of longitudinal control force using either the primary longitudinal control alone or the primary longitudinal control and the longitudinal trim system". The 30lb load is applicable to an aircraft that did not have a powered trim system. This saga has highlighted that the aircraft can be placed in an condition that exceeds the 3 seconds out of trim motion of the trim system. In that respect it is similar to the awareness that grew out of AA587 of the limitations of the term Va in the protection of the structure. The industry learnt from that lack of comprehension and moved on without tails falling off around the circuit. Having an long forgotten technique that exceeds the criteria of 25.255 is hardly comforting, and suggests that remediation is needed, the simplest being by training.
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Old 15th Jun 2019, 02:18
  #416 (permalink)  
 
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Originally Posted by FlightDetent View Post
Only as long as they come at the winning end of it. It is completely meaning less. How do these add in
- military shoot downs
- hijack crashes
- midair collisions caused by the other involved ac
- maintenance losses

As the hull losses - heaven and all hard working people sent - become a scarce occurrence, the outlier events distort any purpose it may have had. And I suggest it never did. It is a PR stunt for the Instagram generation, oh wait..


​​​​
Hull loss rates have been an industry safety benchmark for at least 50 years, and are used, tracked, and published by several aviation safety organizations as well as every major aircraft manufacturer. "Intentional Acts" (terrorism, acts of war, pilot suicide) are routinely excluded as they are obviously not directly related to the aircraft type (I don't know how MH370 is treated since no one really knows if it was an intentional act or not).
Newer aircraft are safer - things like TCAS, GPWS/E-GPWS, improved automatics, more reliable electronic systems, improved warning systems, better engines, etc. have made each generation of aircraft better than the last - do you really want to dispute that simple fact? Even a quick glance at hull loss statistics tell us that the 737NG and the A320 series are amazingly safe (I doubt the small differences between the NG and the A320 series are statistically significant), while outliers like the MD-11 (and yes the MAX) make it obvious that the aircraft type has issues.
Do you think we'd all be better off flying around in 707s and DC-8s?
Or, more to the point, if you don't accept hull loss rates, what metric would you suggest be used for determining how safe various aircraft types are?
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Old 15th Jun 2019, 02:33
  #417 (permalink)  
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Hinged was the wrong word. The axis of rotation I suppose. Right now the H-Stabilizer rotates as though it is hinged well towards the rear. This means it is unstable in the case of failure, though I don't think this has happened but this instability means the load on the jackscrew is almost always there in one direction or another.

As soon as loads leave a theoretical airflow centre, they become exponentially (loosely speaking) greater as the system calls for say, AND. We are now aware of the extreme difficulties caused by this load. We should have been more aware about the jack stalling at least since the Toronto control-unloading emergency which decended 'down to the height of a fuel station sign.'

I bet that got their attention.

If the H-Stabilizer was effectively hinged around a point significantly forward of the centre of the surface it would trail like most control surfaces - at least to some extent.

It occurs to me that any beam to the jackscrew would not need to travel the full range of the surface's angular movement behind the rotation point. Neither would it need to be as strong as the surface is now trailing. i.e., trailing the stabilizer at least eases some of the design loads.

Designed from an armchair? Well, just think about the ramp on aircraft carriers.


.
.

Last edited by Loose rivets; 15th Jun 2019 at 02:50.
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Old 15th Jun 2019, 06:25
  #418 (permalink)  
 
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Originally Posted by fdr View Post
AC25.07D covers the background for 25.255, however the B737 is an aircraft with a powered trim system ergo "it must be possible from an overspeed condition at VDF/MDF to produce at least 1.5 g for recovery by applying not more than 125 pounds of longitudinal control force using either the primary longitudinal control alone or the primary longitudinal control and the longitudinal trim system". The 30lb load is applicable to an aircraft that did not have a powered trim system. This saga has highlighted that the aircraft can be placed in an condition that exceeds the 3 seconds out of trim motion of the trim system. In that respect it is similar to the awareness that grew out of AA587 of the limitations of the term Va in the protection of the structure. The industry learnt from that lack of comprehension and moved on without tails falling off around the circuit. Having an long forgotten technique that exceeds the criteria of 25.255 is hardly comforting, and suggests that remediation is needed, the simplest being by training.

1. Once again, FAR 25.255 is about pilot applied mis-trim, it is a stand alone regulation that has nothing to do with system runaways. Do you have any evidence that FAR 25.255 is not effective for the pilot applied mis-trim case for which it was developed?
If you can make a case which proves that pilot mis-trims actually result in a worse situation than addressed by FAR25.255 best of luck getting the regulators, manufacturers and airlines to show any interest.

33. Out-Of-Trim Characteristics -
§ 25.255. a. Explanation. Certain early, trimmable stabilizer equipped jet transports experienced “jet upsets” that resulted in high speed dives. When the airplane was MISTRIMMED in the nose-down direction and allowed to accelerate to a high airspeed, it was found that there was insufficient elevator power to recover
.

2. The dive recovery requirements of FAR25.255 are agnostic as far as the type of trim system is concerned ergo - I don't understand why you choose a to make some point about powered trim systems.
3. This "saga" has not highlighted anything other than that powered systems can runaway and there are a number of FAR requirements to deal with probability, effect, crew action and time intervals for recognition and reaction. Taking a particular case, the certification recognition time could be 3 seconds and the reaction time a further 3 seconds. So the certification standard certainly recognises that runaways can continue for longer that 3 seconds.
These accidents appear to have been the result of an uninterrupted SAS system runaway - I have no idea on the chain of event which lead to these tradgedies.
4. The story of Va is that a misconception of what Va is was somehow generated in the operational section of the aviation industry. This misconception is still widely held despite attempts to explain the the reality. I see no similarity here. The structural design rules with respect to Va are unchanged.
5. Once again, your "long forgotten technique" has no relevence to FAR25.255 - it is not an issue for a compliant aircraft. I understood that it was a procedure developed for the trim runaway case.
6. Without having access to all the cerification committee meeting minutes, compliance plans, compliance reports this is really a pointless exercise.
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Old 15th Jun 2019, 06:42
  #419 (permalink)  
 
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As of less than a week ago, I could not work out if Boeing have submitted the "Fix" to the FAA officially for re-certification or not - does anyone know for sure?
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Old 15th Jun 2019, 06:56
  #420 (permalink)  
 
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Moving on into the 4th month of grounding now, it's notable there is no positive, straightforward announcement of what is going on. You would expect statements about things being tested from both sides, etc. But nothing. One can only presume there is some deep, unacceptable issue that the parties just cannot agree on.

Regarding announcements about service re-entry, Boeing's various statements about dates which have subsequently proved not to be achieved, and to have had no foundation, must surely now come to the attention of the Securities & Exchange Commission for any impact on their share price. Do many expect it back before 2020 now ?
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