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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 22nd Mar 2019, 08:10
  #2321 (permalink)  
 
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Do I get it correctly that "blowback" of the elevator would be a situation when the actuators for the elevator are not powerful enough to overcome the aerodynamic forces on the elevator, due to high speed (and perhaps an already high angle)?

Is there any indication that a 737 elevator (with nominally working actuators) can be in this situation in some flight regime?
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Old 22nd Mar 2019, 08:50
  #2322 (permalink)  
 
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Originally Posted by fgrieu View Post
Do I get it correctly that "blowback" of the elevator would be a situation when the actuators for the elevator are not powerful enough to overcome the aerodynamic forces on the elevator, due to high speed (and perhaps an already high angle)?
Is there any indication that a 737 elevator (with nominally working actuators) can be in this situation in some flight regime?
See, related: Boeing advice on "aerodynamically relieving airloads" using manual stabilizer trim

and B737 RUNAWAY STABILIZER NNC
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Old 22nd Mar 2019, 09:07
  #2323 (permalink)  
 
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Originally Posted by Smythe View Post
.

[It is amazing the amount of Boeing bashing on this forum. Boeing has made tens of thousands of safe & efficient airliners for more than half a century & that's why there are more Boeings than anything else.]

They pushed the MAX too far, a quick band aid to counter the neo.

A software fix to counter an unstable platform...

tale of the tape...why is MCAS required for certification?
In my humble opinion, they should have started again with the 73 about the time of the -300/-400 and completely redesigned it. As it stands, they seem to have cobbled together systems as they became available or desirable and bolted them where they could find space. (The “computer fuel summing unit” - can’t remember its exact name - is fixed outboard above the F/Os head - why not in the avionics bay?). The F/Os seat cannot be moved vary far back because of the C/B rack behind it. The elevator feel unit has its own pitot probes each side of the fin.

I only have experience of the -300/-400, but that aircraft is a mish-mash of mechanical and electronic devices, seemingly not properly integrated, but just about working. The ‘Classic’ autopilot does not trim ailerons or rudder, so when you take out the autopliot you often have to spend a mile or so on short finals getting the thing trimmed. The Cockpits of the -300/-400 look as if they were “designed” by firing a shotgun at a blank panel, and fitting the instruments and indicators whereever there was a handy hole. Generators have to be manually switched on to the buses. Later models without the round generator dials, still use the old panels with the cut-outs for the round dials rather than making a new panel....how cheap is that?

It seems to me that as each new requirement or problem came along, instead of doing a redesign, Boeing developed a standalone fix or widgit to solve the problem - but they don’t appear to have always thought it through in terms of the way the whole aircraft works, or how the pilots would interface with it.

As to why the 73 is so popular, I think South West have a lot to do with that, (they are also indirectly partly responsible for the arrested development of the 73). I have been told that Boeing also have some very creative fleet purchasing schemes for airlines.

As to MCAS, instead of affecting the THS trim, why not simply have it modify the elevator feel at hiigh AoA - which is, after all, the problem caused by the engine nacelles. Or insert a gentle down input to the elevators? But not the trim. Secondly, why have only one AoA probe, or even two? For such a critical device, why not have five?











Last edited by Uplinker; 22nd Mar 2019 at 10:01.
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Old 22nd Mar 2019, 09:11
  #2324 (permalink)  
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Originally Posted by BrandonSoMD View Post
the stall AOA varies with configuration and weight and other things...
I agree stall AoA varies with configuration, Mach # and others however, I don’t think that, given all other values constant, weight changes AoA. Ie, a wing stops being a wing at the stall AoA, regardless of how much lift is demanded..

I also agree that simply introducing an AoA indication in the cockpit of an airliner will not benefit crews without some education. However, AoA is a fundamental parameter, if it is displayed and obviously in error (deduced by crew education) then it could assist in fault finding. One of the key parts of UPRT (being introduced as mandatory in Europe for all new CommerciL licence training from Dec 2019) is AoA & G awareness. I believe it would be of huge benefit if commercial aircraft had AoA displayed and pilots were educated in its interpretation from day 1 of flying training. P

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Old 22nd Mar 2019, 09:40
  #2325 (permalink)  
 
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Originally Posted by Ian W View Post
There needs to be something like an Failure Modes Effects Analysis that flags up that at this point there are multiple separate warnings being displayed in various ways that will consume the entire cognitive resource of the pilot and not allow his primary AVIATE task any resource.
There needs to be an FMEA which understands the Pilot as being part of the system !
There is extensive FMEA/SSA work done for development and certification of aircraft, but it focusses on the physical systems and makes some simplistic/philosophical assumptions for the pilots. We need to better understand the Pilot as one System out of many which need to work together in an aircraft, which can fail in various ways, can recieve wrong data, can misinterpret things, can follow an inappropriate algorithm (=SOP) etc. Just because the system "pilot" may react sometimes in an unpredictable way is no reason to not include it in the analysis.

We have learned a lot about human factors in the last 20 years, but aircraft design still uses the same man-machine-interfaces like 50 years ago. Some >30 year old design (Airbus A320) is "modern" compared to many other aircraft still being built...
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Old 22nd Mar 2019, 10:02
  #2326 (permalink)  
 
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I've just done a search on PPRuNe for MCAS and the first mention of the phrase at all was December 2018 when news of the Lion Air crash investigation got out. So for a group of several thousand professional fairly nosey/inquisitive bunch of pilots worldwide there hadn't been a sniff of anybody coming across MCAS in some obscure manual and asking what is was. Says it all really.

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Old 22nd Mar 2019, 10:07
  #2327 (permalink)  
 
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Originally Posted by dinbangkok View Post
Regardless of whether you're a pilot or not, surely the question that needs to be answered is simple: How is it remotely OK for Boeing (or any other manufacturer), to sell a passenger aircraft that needs software to correct an aerodynamic imbalance in the design of the aircraft (prone to pitching up)?
By the same reasoning why it was ok in earlier (think 707) models to include an analogue electronic device that does almost exactly the same thing, to bring the 707 in line with the same certification requirement.

Why would it not be ok? All fly-by-wire airliners, i. e. practically all that were developed since the late 1980s, cannot demonstrate unassisted control forces, because it is all artificial. That is even true for fully conventionally controlled aircraft such as the 747. Even the Comet (which predates the 707) had no aerodynamically created control forces, but fully powered flight control surfaces and only a spring-loaded artificial feel system.

Bernd
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Old 22nd Mar 2019, 11:05
  #2328 (permalink)  
 
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Originally Posted by edmundronald View Post
Ok, so we're supposed to believe that the speeded-up certification process of the Max just let ONE bug through.
Or rather, the industry agrees that the best way to search for more bugs is to pull the grounding order, put pilots and SLF in a bunch of planes, and fix whatever happens next.

No wonder the rich refuse to fly commercial.

Edmund
Actually, the rich may not fly commercial but they fly the same aircraft both A and B sell versions of their airliners that have been fitted out as business jets. See Boeing Business Jets



From wikipedia
I have no doubt that there are already 737Max Business Jets.
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Old 22nd Mar 2019, 11:09
  #2329 (permalink)  
 
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Originally Posted by bsieker View Post
By the same reasoning why it was ok in earlier (think 707) models to include an analogue electronic device that does almost exactly the same thing, to bring the 707 in line with the same certification requirement.

Why would it not be ok? All fly-by-wire airliners, i. e. practically all that were developed since the late 1980s, cannot demonstrate unassisted control forces, because it is all artificial. That is even true for fully conventionally controlled aircraft such as the 747. Even the Comet (which predates the 707) had no aerodynamically created control forces, but fully powered flight control surfaces and only a spring-loaded artificial feel system.

Bernd
Nobody is saying FBW is bad, it works fine for Airbus! But if a plane is FBW it should be certified as FBW, which means the failure modes of necessary sensors, control algorithms and servos get carefully analysed by a third party for design weaknesses like a single point sensor failure. Which is where the US process failed with the Max 8 failed egregiously.


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Old 22nd Mar 2019, 11:20
  #2330 (permalink)  
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Originally Posted by dinbangkok View Post
Regardless of whether you're a pilot or not, surely the question that needs to be answered is simple: How is it remotely OK for Boeing (or any other manufacturer), to sell a passenger aircraft that needs software to correct an aerodynamic imbalance in the design of the aircraft (prone to pitching up)?
I was trained to fly over 50 years ago. That involved the Trident. It had a yaw damper - a computer system to counter the basic instability of the aeroplane. Aircraft that require computers are nothing new.

Several people have implied it's perfectly OK for fighters to be unstable but not airliners. I simply can't see the logic in this.

The ironic thing is Airbus take the opposite view - for the most part they take the model that the computers should be involved in all manoeuvring actions. As we know, a similar clash between computers and pilots on an A320 ( XL888T) caused a crash but everybody seems to accuse Boeing of inventing this kind of scenario.

It's a curious situation. There are lots of dodgy things about the Lion crash. The Ethiopian event has not yet - to my knowledge - been definitely attributed to an MCAS malfunction. I think we can all agree it would have been better if pilots had briefed about the potential failure behaviour of MCAS but this might simply have been an oversight on the part of Boeing rather than something cynical.
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Old 22nd Mar 2019, 11:28
  #2331 (permalink)  
 
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Originally Posted by Biseker

Even the Comet (which predates the 707) had no aerodynamically created control forces, but fully powered flight control surfaces and only a spring-loaded artificial feel system.

Bernd
Edmund
Well, yes, but with a Q-Pot as well, giving increasing force with dynamic pressure.
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Old 22nd Mar 2019, 12:11
  #2332 (permalink)  
 
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Originally Posted by andihce View Post
SLF here, but with a background in experimental physics dealing with personnel and equipment safety in large-scale, hazardous experimental situations.

Assuming that both 737 MAX crashes were the result (in large part) of faulty AOA probe data, then we already know, from sad experimental evidence, that relying on one probe is unacceptable. With 2 hull losses in N (? - not a terribly large number) flights of this aircraft, the reliability statistics are hardly at the flight-safety-critical level.

Having an "AOA disagree" warning or AOA readouts for pilots is not necessarily going to help. I suggest that as a minimum, with only two AOA probes (and that should be the minimum number), that MCAS should shut itself down in an AOA disagree situation (with notification to the pilots). The principle here is "primum non nocere". The aircraft is not going to have an upset just because MCAS is not there on these rare occasions.

Furthermore, if AOA data is going to be used in this way (possibly killing people if it is wrong), further sanity checks should be applied to the probe data (e.g., AOA pre-rotation on take-off, consistency with inertial and other air data, whatever).

MCAS as currently implemented seems like a horrid kluge to a non-pilot, but I'm inclined to believe, from what I've read here, that with better engineering (and not too drastic a change) the 737 MAX could be restored to safe service.
I worked in fault-tolerant computing for some time and any single point of failure was something to be avoided at all costs. However, along come the mathematicians who say what is (a) the probability of an AoA failure? What is (b) the probability of a crew not being able to switch off a Stab Trim that is trimming against them - what probability do we have to meet. (c) if (a) * (b) is smaller than (c) -extremely improbable- then you meet the requirement. This type of reasoning is common.
Now that it is apparent that crews are not able to cope with some things unless well trained AND airlines are unwilling to pay for the training. I would expect that first officers are about to be automated out (is flying with HAL any worse than flying with a 25hour MPL?) and in some cases aircraft will become autonomous. Note that MCAS was only there because there was a regulatory concern that human pilots could mishandle the aircraft as the control column loads got lighter. MCAS does not operate with the autopilot controlling the aircraft as that is no safety concern.

Several articles in the media and statements by President Trump are that aircraft are too complicated. So are aircraft getting too complicated to fly? Or should that be that aircraft are getting too complicated for humans to fly?
In a world where there are unmanned jet aircraft operating from carriers and doing air-to-air refueling, flying a 737 is seen (rightly or wrongly) as a simple task to automate - yes even a Cat II landing in an on the limits blustery cross wind to a wet runway.

And before people ask: Yes I would fly as pax in an autonomous aircraft.
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Old 22nd Mar 2019, 12:20
  #2333 (permalink)  
 
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Originally Posted by HarryMann View Post
Well, yes, but with a Q-Pot as well, giving increasing force with dynamic pressure.
Sure, the point was, all of it was artificial even that early. So why get all worked up about one small system that does the same thing now? That it was perhaps not done and analysed as diligently as it should have is one matter, but the idea of enhancing control forces artificially is literally as old as jet airliners. Perhaps older, I haven't looked into piston-powered airliners in any more detail.

Bernd

P.S. my post is gone, I wonder why it was deemed irrelevant or bad or inappropriate or whatever. But I guess I'll never know. Just because I don't have an ATPL I cannot talk about certification criteria and risk assessment?

Last edited by bsieker; 22nd Mar 2019 at 12:39.
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Old 22nd Mar 2019, 12:57
  #2334 (permalink)  
 
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Originally Posted by twistedenginestarter View Post
I was trained to fly over 50 years ago. That involved the Trident. It had a yaw damper - a computer system to counter the basic instability of the aeroplane. Aircraft that require computers are nothing new.
Sure. All swept wing airliners are susceptible to dutch rolls and require yaw dampers. The 707 had one in all models.

Several people have implied it's perfectly OK for fighters to be unstable but not airliners. I simply can't see the logic in this.
In case you really are serious:

For fighters, maneuverability is supremely important, and maximum maneuverability can only be obtained with relaxed aerodynamic stability. That additional safety layer has been dispensed with in fighters to increase their effectiveness as machines of war. Military transport aircraft are as stable as civil airliners. Airliners might be made a bit more efficient by relaxed stability, but that tradeoff is not appropriate when carrying passengers for whom being killed is not part of the everyday risk.

The fighters, as flown by the pilots, are completely stable, it's just all computer-assisted. Unlike airliners, most modern fighter jets would literally break apart (depending on the speed) and fall out of the sky should all flight control computers fail (as would the B2, but the reason is the stealth-shape, which is much easier to obtain with relaxed stability). So if anything you'd want them to be more reliable than in aerodynamically stable transport aircraft (civil or otherwise).

The ironic thing is Airbus take the opposite view - for the most part they take the model that the computers should be involved in all manoeuvring actions. As we know, a similar clash between computers and pilots on an A320 ( XL888T) caused a crash but everybody seems to accuse Boeing of inventing this kind of scenario.
You seem to have missed that all Boeing airliners (and Embraer, and Bombardier) since and including the 777 have been 100% fly-by-wire. It isn't an Airbus thing. I also don't know why you would call it "ironic".

Also, the XL Airways Crash in Perpignan was very different. Yes, two faulty AoA sensors were a causal factor, but it crashed because the pilots deliberately stalled it at very low altitude, testing the protection system which they blindly believed would save them, but which wasn't working because of the frozen AoA sensors. It was overreliance on automation (and also poor planning and execution of flight tests), but it has nothing to do with computers fighting against humans or any such nonsense. Quite the opposite. It crashed because the computers were not able to save the pilots from themselves. Which a perfectly fine airplane would have done.

Bernd

Last edited by bsieker; 22nd Mar 2019 at 14:09. Reason: Minor typo.
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Old 22nd Mar 2019, 13:10
  #2335 (permalink)  
 
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Originally Posted by Ian W View Post
In a world where there are unmanned jet aircraft operating from carriers and doing air-to-air refueling, flying a 737 is seen (rightly or wrongly) as a simple task to automate - yes even a Cat II landing in an on the limits blustery cross wind to a wet runway.
How about a squall line extending 1,000 miles across the intended flight track?

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Old 22nd Mar 2019, 13:14
  #2336 (permalink)  
 
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I read a lot of Airbus Boeing finger pointing but I think in both one needs to understand the systems to fly. As hopefully everybody understands now how to disconnect the horizontal stab from it’s muscle I rest my case. It looks like basic understanding of airplane fundamentals still goes a long way even today and both crews should have never flown the airplane without it, assuming the Ethiopian plane had the same problem as the Lion air of course.
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Old 22nd Mar 2019, 13:43
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Originally Posted by efatnas View Post
I read a lot of Airbus Boeing finger pointing but I think in both one needs to understand the systems to fly. As hopefully everybody understands now how to disconnect the horizontal stab from it’s muscle I rest my case. It looks like basic understanding of airplane fundamentals still goes a long way even today and both crews should have never flown the airplane without it, assuming the Ethiopian plane had the same problem as the Lion air of course.
That's fine efatnas, providing you know that those airplane fundamentals have changed... aren't we being told that communication and documentation from Boeing on MCAS was lacking or certainly insufficient .. considering this system messed in a previously unheard of way with the stabiliser trim ?
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Old 22nd Mar 2019, 13:47
  #2338 (permalink)  
 
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You're right, Harry, Boeing should have told the crews. "If you're out doing flaps up stalls in your MAX, you will get an intervention from MCAS. Also, if you get a continuous stick shaker on take off rotation & are stupid enough to accelerate, clean up the flaps, & try to continue the flight with the stick shaker, you MAY get a repeated intervention from MCAS 'cause it thinks the airplane is stalling".
The second sentence here is only true if Boeing had realised that this could be the outcome of a single AOA source failure. If they had that knowledge and did nothing about it, then the courts will no doubt take that into account in due course because the failure to communicate it or manage the risk would indeed be seen as cynical. Please don't construe this as Boeing bashing - that would be as unhelpful as trying to shift responsibility to the perceived shortcomings of the two operators concerned. Play the ball rather than the man.

Regardless of what manufacturer or operator is involved, the question for me is whether the fault tree analysis (or whatever process was used) and the subsequent sentencing of risk regarding 'system X' during its design and checkout provided sufficient evidence to the regulator that system X was safe to be fielded. And IF the regulator falls into the trap of regulatory capture (still to be determined...) or does not have the necessary resources to satisfy itself that the manufacturer's claims are accurate, then the regulator could and should be held to account. In a safety-critical environment it should never be possible for a manufacturer in any country to mark its own homework.

If you would like an example of how this situation can occur anywhere, take a look at the airworthiness failure that killed 14 UK servicemen in Afghanistan in 2006 - you can read the lawyer's analysis of the process failings here
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Old 22nd Mar 2019, 13:48
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Originally Posted by aterpster View Post
How about a squall line extending 1,000 miles across the intended flight track?
The FOC/Command Center/Network Manager would deal with that in the same way it currently does. If the UA was flying completely autonomously, then that kind of major weather system would be one of the use cases that it was designed to meet. There is research in hand with Decision Support Tools to provide just that kind of assistance to self-dispatching operators. Aircraft these days fly in a sea of usually discarded/disregarded information.
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Old 22nd Mar 2019, 13:59
  #2340 (permalink)  
 
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As we know, a similar clash between computers and pilots on an A320 ( XL888T) caused a crash but everybody seems to accuse Boeing of inventing this kind of scenario
. The Perpignan accident was brought about by testing to the stall an aircraft which had been standing long term at end of lease, and then had major maintenance work done - at 2,000 feet. And the AOA detectors being tested did not work. Quite why they were practicing a stall at a height you wouldn't even attempt in a Cessna on a PPL skill test is not apparent. It's like the Habsheim incident, playing about at a ludicrously low altitude. Let's call it an Andy Hill moment. Except that for these ones they then tried to stick it on the automation.
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