Grumpy Git
On Moderation
I fly maybe 25 times a year. As an engineer there is no way I'll be booking anything on a 737 Max8 when (if) it gets re-certified.
-
Our new ticketing site is now live! Using either this or the original site (both powered by TrainSplit) helps support the running of the forum with every ticket purchase! Find out more and ask any questions/give us feedback in this thread!
Boeing woes
- Thread starter Grumpy Git
- Start date
- Status
Sponsor Post - registered members do not see these adverts; click here to register, or click here to log in
R
RailUK Forums
TrafficEng
Member
I've watched the programme. The way the reconstructions have been edited doesn't give a very good representation of what it was really like. In my view it is overly dramatised and compressed. I'd advise anyone who wants to better understand the accidents to read the accident investigation reports instead.
As an example, it is implied that MCAS started to work as soon as each aircraft left the ground. That isn't the case, MCAS wasn't active until a later stage of the flight. The reconstruction was very 'light' on what happened in the time between rotation and the first activation of MCAS in each case.
I find it more worrying that the media narrative is focused on Boeing, and particularly on the design and engineering. These accidents were just symptoms of far wider and deeper issues within the worldwide aviation industry.
TrafficEng
Member
As an engineer myself (with a non-normal interest in flight safety) I'd say that response is difficult to understand.
If the Max is re-certified we should be fairly confident that a thorough review of all safety critical design decisions has been competently carried out. If not, then we should have no confidence that the worldwide system of aircraft certification is fit for purpose. In that situation stepping onto any aircraft would be unwise.
Boeing themselves need to make the Max (or its rebranded equivalent) safer than anything else flying at the present time. Another crash would have the potential to kill the company, they simply cannot afford to let that happen.
I would have far more interest and concerns over who was sitting in the pointy end of thing. In particular how many years they had been doing the job, and what percentage of that had been spent controlling an aircraft manually themselves, rather than pushing some buttons and sitting back relaxing until shortly before the start of the arrival descent.
DaleCooper
Established Member
I've read your contributions with interest, you are obviously someone with far more knowledge than me on this subject however I can't let this go by without comment:
Two 737MAX aircraft have crashed in similar circumstances with the loss of hundreds of lives. If this isn't about Boeing and their engineering and design then what is it about? If they are symptoms of "far wider and deeper issues within the worldwide aviation industry" why are other aircraft still flying (and not crashing) whereas 737MAX are grounded?
Two 737MAX aircraft have crashed in similar circumstances with the loss of hundreds of lives. If this isn't about Boeing and their engineering and design then what is it about? If they are symptoms of "far wider and deeper issues within the worldwide aviation industry" why are other aircraft still flying (and not crashing) whereas 737MAX are grounded?
TrafficEng
Member
Some good questions there. My initial response would be why do you think other aircraft are not crashing? Is that based on a statistical analysis, or that you've not seen/noticed any others on the news? (That isn't a criticism directed at you btw, it is a reflection on the way the media produce news and how we consume it).
To get a more rounded view of the problems I'd suggest the starting point should be reading the accident report for the AF447 crash in 2009. That wasn't a Boeing, but gives insights into human factors and how pilots deal with situations in the cockpit. It illustrates the 'battle' humans can have trying to understand what complicated computer driven systems on aircraft are doing, especially in situations of stress. Also worth noting that despite the cause of the aircraft loss being unknown, the A330 fleet was not grounded.
https://en.wikipedia.org/wiki/Air_France_Flight_447
The second example worth looking at is the A400M accident in 2015. I'd pick that one not because it is another Airbus case, but demonstrates the issues are not limited to low-cost air transport where cost-savings are a priority. Deadly software issues can happen on military aircraft as well.
https://en.wikipedia.org/wiki/Airbus_A400M_Atlas#Accidents
The third one I'd recommend reading about is the Atlas/Prime flight 3591 from February this year. A Boeing, but a 767 not a 737. After people got bored watching the video footage of the plane plunging from the sky it has all but vanished from media coverage and public awareness. Is that because it was a freighter and 'only' the three crew were killed? What if it crashed a few minutes later when it was over a populated area, instead of a swamp?
https://en.wikipedia.org/wiki/Atlas_Air_Flight_3591
I've added Wikipedia links to all three examples only to allow others to identify the flight/incident in question. I would urge people who are interested to locate a copy of the accident investigation report and read it in full.
To respond to your final point, the global economy turns on the ability of the aviation industry to shift people and goods around the world for a pittance. There is a tacit acceptance that some people will die each year to keep the system going (a similar view applies to road transport). If aircraft were grounded until everything was fixed to a level people might imagine exists then the economic and social consequences would be severe.
Peter Mugridge
Veteran Member
It would, but they tried to counter that by introducing something else which the MCAS was supposed to keep an eye on. I've forgotten what the counter measure was, but I think it's described in the documentary someone else linked to this afternoon.
Another issue is the "15% different" rule for a shorter certification process. It should be changed to be "15% different from the FIRST version of a given aircraft, not 15% different from the most recent version. When you consider that we have had, so far, the following versions:
-100 ( the original )
-200
-300
-400
-500
-600
-700
-800
-900
...then the MAX followed on from there; if all of these were the maximum 15% different from the previous version ( they weren't - this is illustrative only ) then it's easy to see that the 15% rule can result in something that should really be getting the full long drawn out certification process getting put through only the abbreviated procedure. That cannot be good can it?
Edited: Because I made a typo in the initials of the system involved and thought I should correct it!
Last edited:
TrafficEng
Member
This isn't something I've heard of before, although that obviously doesn't mean it doesn't exist. If you can find a source for that information it would be really interesting.
But taken at face value it seems odd that a dynamic system like MCAS would be involved in counteracting something which is static. The impact of the new engines on the centre of gravity doesn't change during flight as their mass and position doesn't alter (significantly). If the engines have changed the balance of the aircraft then the solution is simply to move something else (or add ballast) to restore the CofG. Once that is done then no further action is required. (notwithstanding changes of CofG per flight resulting from passenger/luggage/freight/fuel loading)
The trim system itself would normally be used to manage the control forces required to maintain the required attitude, given those variables in different phases of the flight.
There is another system on the 737 called Speed Trim System (STS). This automatically adjusts the trim in response to changes in thrust/speed. In normal flying the STS will make adjustments (visible to the pilots as the trim wheels spinning round). STS has been 'linked' to the MCAS issue because pilots can become conditioned to seeing the trim wheels spinning (on an apparently random basis) during flight (as part of normal STS operation) and therefore might be less likely to notice when they suddenly start spinning as a result of MCAS activation.
Bletchleyite
Veteran Member
But they didn't only change the balance (though they did change that). They also changed the rotational force around the wing that is exerted by them not being in line with it due to their different position. That is a dynamic change - the effect varies by how much power is being requested from each engine at any given time - the main effect being that powering up will pull the nose up and powering down will let it drop again (which is what MCAS is partly counteracting, though I think airflow over the nacelles also had an effect, hence it needing to know airspeed rather than just throttle position). (Google the Sioux City crash for how that was used to save many passengers, though sadly not all, when crash-landing a basically uncontrollable aircraft).
Greybeard33
Established Member
As I understand it the issue is that, at high angle of attack (approaching the stall), the airflow over the top of the engine nacelle creates aerodynamic lift. Because the nacelle is so far forward of the centre of gravity, this lift creates a substantial nose up pitching moment, additional to, and independent of, the effect of the engine thrust. This pitch up moment opposes the natural tendency of the wing to pitch nose down as the stall is approached. The nose drop tendency is needed to identify the stall as required by the airworthiness regulations - the aircraft will recover from the stall by itself unless the pilot keeps pulling back hard on the stick.
The MCAS is intended to trim the horizontal stabiliser in the nose down direction in this scenario, thereby creating a nose down pitching moment that counters the lift from the nacelles and replicates the stick force characteristics of previous 737 models.
AFAIK there is no public domain information on the natural stalling characterisitcs of the MAX with MCAS disabled. Therefore it is unclear if MCAS really is, as Boeing claims, merely an augmentation system that ensures that the "stick force gradient" at high AoA complies with the regulations, or if it is effectively a stall identification system, without which the stall would not be sufficiently evident to the pilot. The distinction is important, because the regulations require that a stall identification system must be fail-operative like a fly-by-wire system, i.e. continue to function properly after any single failure. The existing MAX avionics hardware is fundamentally incapable of fail-operative MCAS capability. A third AoA sensor would be needed (as fitted to Airbus aircraft) in order to vote out a faulty sensor.
Boeing has not released details of its proposed MCAS fix, but it is reported to be software only, intended to make the system fail-passive. If the two AoA sensors disagreed, the MCAS functionality would be disabled automatically.
TrafficEng
Member
Absolutely. My post was a response to the discussion between Gooner18 and Peter which was limited to the impact of the engine change on CofG.
That impact is fixed, in a nose-down sense. MCAS wouldn't be an obvious solution to that.
Sioux City is an incredibly interesting case, and often used as an example of excellent CRM. A valid question is whether any of the three Max incidents would also be cited as examples of good CRM, not withstanding the difficulties Boeing handed them.
Shaw S Hunter
Established Member
Some points worth considering.
The basic architecture of the 737 family is over 50 years old and reflects a now outdated design priority for an aircraft that sits low to the ground. The improvements in jet engine technology have led to much larger diameter engines which have always posed something of a design problem for Boeing even before the MAX. As such Boeing really should have come up with a clean sheet replacement design instead of another 737 iteration. But this would have cost lots of development money as well as risking the continuation of the cash cow that the 737 represents for Boeing. And the likes of Southwest Airlines and Ryanair would have been "disappointed" if continued fleet modernisation had necessitated additional training costs. It could be said that Boeing got fat and lazy!
As well as the issues around MCAS there are also suggestions that there is not enough understanding of the aerodynamic interaction more generally between the engine nacelles and the wing leading edges in the high-and-forward engine configuration adopted for the MAX. Not a good position to be in for certification issues.
There is also an increasingly significant cultural issue which seems to be much worse for Boeing, as an American company compared to Airbus, which relates to the flying experience of pilots before they get near the airline industry. In the US there is significantly more private flying than anywhere else in the world so that some people are learning to fly at the same age as they learn to drive. This is inevitably reflected in the attitude shown both by Boeing and many US commentators to pilot training requirements given that most budding US airline pilots already know all about basic stick and rudder flying. But in less developed parts of the world, which are experiencing massive growth in demand for air services, very few pilots have done any flying at all before starting with an airline. And this is arguably also a problem for the certifying authorities when it comes to the enforcement of consistently high safety standards on a global basis. The continued delay in re-certifying the MAX may well be related to this as much as the obvious technical issues.
As to whether the MAX's woes pose an existential threat to Boeing I suspect not. Profitability at its Commercial Aircraft division may well take a hit for a year or few but its defence contracts are so lucrative that its future as a whole is reasonably secure. And in any case Airbus doesn't have the capacity to replace very much of Boeing's lost production.
The basic architecture of the 737 family is over 50 years old and reflects a now outdated design priority for an aircraft that sits low to the ground. The improvements in jet engine technology have led to much larger diameter engines which have always posed something of a design problem for Boeing even before the MAX. As such Boeing really should have come up with a clean sheet replacement design instead of another 737 iteration. But this would have cost lots of development money as well as risking the continuation of the cash cow that the 737 represents for Boeing. And the likes of Southwest Airlines and Ryanair would have been "disappointed" if continued fleet modernisation had necessitated additional training costs. It could be said that Boeing got fat and lazy!
As well as the issues around MCAS there are also suggestions that there is not enough understanding of the aerodynamic interaction more generally between the engine nacelles and the wing leading edges in the high-and-forward engine configuration adopted for the MAX. Not a good position to be in for certification issues.
There is also an increasingly significant cultural issue which seems to be much worse for Boeing, as an American company compared to Airbus, which relates to the flying experience of pilots before they get near the airline industry. In the US there is significantly more private flying than anywhere else in the world so that some people are learning to fly at the same age as they learn to drive. This is inevitably reflected in the attitude shown both by Boeing and many US commentators to pilot training requirements given that most budding US airline pilots already know all about basic stick and rudder flying. But in less developed parts of the world, which are experiencing massive growth in demand for air services, very few pilots have done any flying at all before starting with an airline. And this is arguably also a problem for the certifying authorities when it comes to the enforcement of consistently high safety standards on a global basis. The continued delay in re-certifying the MAX may well be related to this as much as the obvious technical issues.
As to whether the MAX's woes pose an existential threat to Boeing I suspect not. Profitability at its Commercial Aircraft division may well take a hit for a year or few but its defence contracts are so lucrative that its future as a whole is reasonably secure. And in any case Airbus doesn't have the capacity to replace very much of Boeing's lost production.
The issue is not that other aircraft don't crash, the issue is that they don't crash at the same rate. Almost 1500 A330s has been built and it has been in service since 1994. When AF447 crashed, it was the first fatal accident with an A330 in commercial service (one crashed in Toulouse during a test flight). There was a 2nd fatal accident a few months later but that is two fatal accidents in 25 years with 1500 planes. And the "sister model" A340 with 380 built has never been involved in a fatal accident during its 26 years of service.
The 737MAX however has crashed twice in less than two years of commercial service with 387 aircraft delivered.
TrafficEng
Member
The raw rate of accidents isn't really a helpful measure given the small numbers involved. What conclusion can you draw if a high rate of accidents happen with a particular model, but the nature and cause of the accidents varies widely?
The approach is also flawed if you compare (say) an A330/A340 with (say) a 737 when the role of the aircraft is very different. Given take off and landing is typically higher risk than cruising you might expect a higher rate of accidents in short-haul aircraft that spend a greater percentage of their lives taking off and landing than long-haul aircraft do.
The specific issue with the Max was that two accidents happened with apparently the same basic cause, and the mitigation steps introduced after the first accident appeared to be ineffective at preventing the second one.
That post (and this one) wasn't a defence of the 737 Max safety record. It was a challenge to the assertion that other aircraft aren't crashing.
That's almost true. The real issue was that MCAS v1 turned itself back on after being turned off in the usual way. In addition, the raison d'etre for MCAS (making the Max fly the same as the NG) meant that many (most?) pilots were never even told it existed.
So yes, had the pilots completed an untrained procedure to turn off a system that they had never been told existed then they would have had a perfectly flyable aircraft.
Edit: Hadn't read far enough in the thread to see these points being raised.
Last edited:
They more than likely didn't leave the throttles on full thrust, that would have been the autothrottle system. It has a "glitch" where, if you level out early during the climb, it will maintain TOGA.
It's a known issue so, you could argue, they should have been able to recover it, but at what point do you stop blaming the pilots for not being able to apply workarounds?
Grumpy Git
On Moderation
The forces on the horizontal stabiliser were so great at the end it was impossible for the pilots to manually operate the jockey wheels.
Last edited:
Peter Mugridge
Veteran Member
It would be either within the documentary someone linked to yesterday, which I watched when it was first broadcast, or would have been within articles in the Daily Telegraph; I don't try to remember where I see things like that as long as I know the source is fairly reliable when I see it.
However, it appears that other posters overnight have already filled in a lot of the detail about it.
I would think it's highly unlikely any commercial manufacturer would add ballast anywhere except as a last resort because of the adverse impact on fuel consumption and reducing the payload.
That's closely related to the point of the issue caused by the 15% difference rule that I mentioned yesterday - they've basically got a half-new aircraft through on less than full certification because each new variant is being compared to the previous one rather than the original one.
Last edited:
TrafficEng
Member
MCAS doesn't switch itself back on. Strictly speaking it is never switched off. The correct procedure on identifying unwanted/unexplained pitch adjustments [from any cause] is to isolate the trim motors. This is done manually by the pilots and cannot be undone by any automatic process.
Much emphasis has been placed on the pilots not knowing about MCAS, but the runaway stabiliser procedure is designed to deal with a symptom (e.g. unwanted/unexplained pitch adjustments) that could have one or more causes. The pilots do not need to know the cause in order to apply (from memory) a 'fix' which at the minimum will stabilise the situation giving them time to carry out further troubleshooting.
Anyone relying on pilots not knowing about MCAS to place all the blame on Boeing should explain what they would expect pilots to do in the event (say) of a short-circuit in trim control system.
The correct procedure is not just trained, it is a memory item. Pilots are expected to be able to do it immediately and correctly without needing to refer to the manual.
Dealing with unreliable airspeed is not a 'workaround'. It is another procedure pilots should be able to complete from memory.
"Item 2. Autothrottle (if engaged)....Disengage"
"Item 4. Set the following gear up pitch attitude and thrust:....[80% N1]" (my emphasis)
I would suggest the point at which the "blame" might stop would be once the pilots had correctly completed the memory items from the Airspeed Unreliable NNC. According to the accident investigation report the First Officer was struggling to even find the procedure in the quick reference handbook.
DaleCooper
Established Member
The impression I'm getting from this thread is:
The pilots were at fault
Boeing did nothing wrong
Other planes crash (but are not reported in the media)
The air transport industry as a whole is to blame
The pilots were at fault
Boeing did nothing wrong
Other planes crash (but are not reported in the media)
The air transport industry as a whole is to blame
Grumpy Git
On Moderation
Me too.
TrafficEng
Member
Where did you read that?
The position that there are many factors involved and no one party is wholly to blame is a lot more reasonable than the alternative (and frequently expressed) view that one party is 100% to blame.
You don't need to take my word for that, just read the independent air accident investigation report for Lion Air 610.
Greybeard33
Established Member
Attempting to apportion blame to the pilots is a Boeing diversionary tactic. These crashes would not have happened if the MAX design had complied with the applicable airworthiness requirements. That is why the aircraft was grounded.
Edit:
It remains to be seen if Boeing can convince the FAA and international airworthiness authorities that the proposed software modifications are sufficient to allow the MAX to go back into service.
Edit:
It remains to be seen if Boeing can convince the FAA and international airworthiness authorities that the proposed software modifications are sufficient to allow the MAX to go back into service.
GRALISTAIR
Established Member
Is the usual ballast DU ( depleted uranium) or is that just internet folklore ?
DaleCooper
Established Member
As I said it is an impression I have received from posts such as:
GRALISTAIR
Established Member
I did 107 flights this year - lowest for 10 years btw- and there is no way I will willingly get on one either
edwin_m
Veteran Member
I think this gets to the nub of the issue. A perfect pilot in perfect circumstances might have been able to recover the situation, but if the pilot is less experienced or less trained, and something else is causing a distraction? Do you blame the pilot or the company? Particularly pertinent is the issue that Boeing were trying to avoid requiring the pilots to take extra simulator training, which might have given them that extra knowledge and confidence about how and when to intervene if the system let them down.
Chesley Sullenberger is a pilot of long experience and probably the public's epitome of the hero in the cockpit, yet... https://sanfrancisco.cbslocal.com/2...ullenberger-boeing-737-max-flight-simulation/
Funny that. Having read the thread this morning I get exactly the same impression.
Grumpy Git
On Moderation
Basically Boeing gave pilots (and the FAA) the impression that flying the Max8 was exactly the same as flying any other 737 and this is clearly far from the truth.
TrafficEng
Member
Not since 1981, apparently.
https://www.pprune.org/tech-log/479994-depleted-uranium-used-ballast-747-a-2.html
GRALISTAIR
Established Member
Exactly and imho the whole crux of the issue
- Status