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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 8th Jun 2019, 06:33
  #221 (permalink)  
 
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I bet the 777X is not on an accelerated certification schedule anymore....
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Old 8th Jun 2019, 07:41
  #222 (permalink)  
 
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Originally Posted by 568 View Post
Flight museums?
Perhaps Boeing should suspend production ! That of course brings other issues to light. But to build or not to build, that is the question.
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Old 8th Jun 2019, 08:32
  #223 (permalink)  
 
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I thought the software fix was in and that the aircraft had done a few hundred test flights and found to be fine - safe and ready for return.
One has to wonder whether self certification will be the feature of future releases.
Trust is an unquantifiable figure on the balance sheet - except for accountants of course
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Old 8th Jun 2019, 11:57
  #224 (permalink)  
 
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Originally Posted by Gove N.T. View Post
I thought the software fix was in and that the aircraft had done a few hundred test flights and found to be fine - safe and ready for return.
I suspect that the new software isn't what's holding up the show. In the course of examining these accidents some other issues have come to light (like the difficulty in using the manual trim wheel is some situations) and the level of trust in Boeing and the FAA are at an all time low. Some regulators may also require sim training, and there are currently not enough sims to accommodate all the operators. This will take longer than anyone initially thought.
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Old 8th Jun 2019, 14:19
  #225 (permalink)  
 
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Damned if they do and damned if they don't, Boeing want to get the aircraft back in the air asap however the fix has to be 100% because if there is another accident that's the end of the MAX. Boeing would then be left with several hundred unsellable aircraft which have cost them billions to produce and will be worth scrap value. They will lose their bread and butter income and have to survive on the B777/B787 and military contracts for several years whilst they need to fund the development of an all new replacement narrowbody which will be looked at sceptically by potential purchasers.

The British aircraft industry was dominant after WW2 until the Comet disasters, by the time the design flaws were sorted out the type had been overtaken by the B707 and British aviation never recovered. The Chinese C919 is only a couple of years away from first deliveries and might prove to be a credible option for airlines which are unable to secure Airbus A320s. If the C919 is a commercial success, Boeing will struggle to regain their position in the market and could be reduced to number three in the narrowbody arena behind Airbus and Comac. If the MAX is permanently grounded this would give a huge leg up to the Chinese aerospace industry and whilst the C919 currently falls short of current Airbus/Boeing types in terms of performance, once the orders and money start coming in improvements will soon follow.
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Old 8th Jun 2019, 14:44
  #226 (permalink)  
 
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Simulator capacity

Originally Posted by yoko1 View Post
I suspect that the new software isn't what's holding up the show. In the course of examining these accidents some other issues have come to light (like the difficulty in using the manual trim wheel is some situations) and the level of trust in Boeing and the FAA are at an all time low. Some regulators may also require sim training, and there are currently not enough sims to accommodate all the operators. This will take longer than anyone initially thought.
Simulator capacity needn’t be an issue, MCAS is not much more than a bolt on to the existing STS ( speed trim stability) system, therefore it would be relatively easy to put a software package on the NG simulators to mimic the MAX.

Having flown both, from a pilots perspective the NG/MAX are closer to each other than the CL/NG in terms of general handling, indeed this is how it was designed to be!

The crux of this is how to identify and deal with STAB TRIM RUNAWAY, the problem for the manufacture is that the QRH qualifies that statement by adding the word “continuously” to STAB TRIM RUNWAY condition statement and the MCAS does not result in the stab trimming running continuously, but rather 5 secs of stab movement to push the nose down, it only does it once, unless you ( as you will) trim nose up, then MCAS resets and trims down again, meanwhile unless you pull the power back the aircraft continues to accelerate requiring more trim, this whilst you’re trying figure what is going on! eventually you’ll either run out of height or elevator authority from which there is only one outcome.

In in the industry we are already seeing crews in sim sessions assuming that in the LVO section 6 thinking that they have a trim runway when the trim systems start to trim nose up at 400 during the auto land in preparation for a possible dual channel go around and pressing TOGA when in fact all is well......

What ever the eventual fix it has to be bullet proof.
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Old 8th Jun 2019, 14:44
  #227 (permalink)  
 
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Originally Posted by krismiler View Post
if there is another accident that's the end of the MAX.
If there is another accident attributable to MCAS then the risk is to Boeing as a whole and not just the MAX
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Old 8th Jun 2019, 14:58
  #228 (permalink)  
 
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Unlikely but possible

Originally Posted by krismiler View Post
Damned if they do and damned if they don't, Boeing want to get the aircraft back in the air asap however the fix has to be 100% because if there is another accident that's the end of the MAX. Boeing would then be left with several hundred unsellable aircraft which have cost them billions to produce and will be worth scrap value. They will lose their bread and butter income and have to survive on the B777/B787 and military contracts for several years whilst they need to fund the development of an all new replacement narrowbody which will be looked at sceptically by potential purchasers.

The British aircraft industry was dominant after WW2 until the Comet disasters, by the time the design flaws were sorted out the type had been overtaken by the B707 and British aviation never recovered. The Chinese C919 is only a couple of years away from first deliveries and might prove to be a credible option for airlines which are unable to secure Airbus A320s. If the C919 is a commercial success, Boeing will struggle to regain their position in the market and could be reduced to number three in the narrowbody arena behind Airbus and Comac. If the MAX is permanently grounded this would give a huge leg up to the Chinese aerospace industry and whilst the C919 currently falls short of current Airbus/Boeing types in terms of performance, once the orders and money start coming in improvements will soon follow.
I think a permanent ground unlikely, I guess Boeing could always restart the NG production, something 14% less fuel efficient but in the eyes of the public safe might work as a stop gap, Boeing’s leverage would be on pricing and that fact that Airbus production is sold out half a decade in advance, for 90% of the route market it does the job and on shorter sectors there will be little difference in cost per seat per kilometre, Boeing would have to go for a quantum leap aircraft that puts it way ahead of Airbus narrow body, composite, bleeds less with a nose that looks like a mini Dreamliner or A350 rather than a red London bus, a 20% fuel burn saving ought to be achievable.

I bet Boeing wished they’d trusted their original judgement to go for a clean sheet rather than be railroaded by south west and other big 73 buyers into keeping a common type rating.
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Old 8th Jun 2019, 15:55
  #229 (permalink)  
 
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Simulator capacity needn’t be an issue
Not sure where you are located, but sim time has been at a premium for quite a few years. Used to be, if we wanted to check something out quick, we could just run down to the sim, not anymore. Booked up with all the newbies especially.

The crux of this is how to identify and deal with STAB TRIM RUNAWAY
MCAS isnt stab trim runaway. If it was that simple, there would simply be an off switch. MCAS was a cure for the problems, but doesnt solve the problems.
You have high AoA stall, low speed stall, and high G maneuver stall problems to deal with. That is not a dashboard light and software patch fix.

I thought the software fix was in and that the aircraft had done a few hundred test flights and found to be fine - safe and ready for return.
According to Boeing, the software fix has not been submitted to the FAA for review. It also appears that the 'testing' has been, for the most part, in the sim, not actual flights.

Currently, the Congressional Committee is handing the Lazy B theirs B's.
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Old 8th Jun 2019, 16:22
  #230 (permalink)  
 
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Originally Posted by krismiler View Post
If the MAX stays grounded until the end of this year, which is quite likely, then with current production rates and the number already sitting on the ground, we could be looking at nearly 700 aircraft parked.

Many airlines would be unable to have all their aircraft on the ground at their home base at the same time due to lack of space and rely on the fact that most of the time they will be in the air or turning around at out stations.

The MAXs already in service at the start of the grounding are reasonably well dispersed worldwide, however with the number already produced since they stopped flying and 40-50 more coming out of the factory doors each month, where are Boeing going to store them ?
Perhaps they can be stacked? But it will make quite an interesting photo... a few hundred brand new 738Ms parked somewhere. And when return to service does occur, it will take several months at least for the stored backlog production to be delivered, accepted and entry into service.
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Old 8th Jun 2019, 17:54
  #231 (permalink)  
 
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Smythe, et al.
There was no need to change the basic MCAS algorithm. It was ‘tried and tested’, and certificated.
The safety issue involved the integrity of the AoA input to the computation, where an error resulted in unanticipated trim operation due to weaknesses in the implementation - design good, engineering and certification not so. Without changing or improving the AoA vane, the initial solution (1) concentrated on limiting the effect of an erroneous value; cross comparison of sensors, limiting the extent and rate of trim.
Apparently this did not meet with regulatory approval, thus a revised version is being considered.
Most system testing and validation could be completed with ground simulation / stimulation of the overall system. A test flight would validate the integrity enhancement with ‘simulated’ in-flight failures. Also it would be expected that the certification authorities require demonstrations of flight handling with MCAS disabled and any limitations in operation.

The extent of the flight tests is surprising and more likely to be related to other issues arising from the accidents; particularly the trim runway drill and the apparent inability to use the trim wheel or elevator to pitch the aircraft.
This might involve additional modification and flight testing; see tech discussions earlier in this thread.

1) https://www.boeing.com/commercial/73...e-updates.page



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Old 8th Jun 2019, 17:55
  #232 (permalink)  
 
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Salute!

Not so sure the Max will survive, and even with more and low-priced NG variants, folks will still be leery of buying the planes as long as it has "737" in the model number.

Back in the day Lockheed bit the bullet on the Electra and did major hardware/aero fixes. The result wound up as the P-3 ASW platform and served for over 4 decades, and even now being replaced by P-8's. However, public trust had been lost and Lockheed walked away from the commercial market and sold P-3 planes to all comers.

The looming, myriad of trials has yet to begin, and their publicity will not impress folks that discover their ride to visit grandma is one of the "fixed" Max platforms.

Only way Boeing can survive is to stop selling the MAX with MCAS. Fix the aero problem and advertise "no MCAS required", or simply stop selling the model and take the $$$ hits.

Gums opines...

Last edited by gums; 8th Jun 2019 at 18:57.
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Old 8th Jun 2019, 18:25
  #233 (permalink)  
 
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Yo gums,
As discussed previously, an aerodynamic correction (‘fix’) might not be particularly easy, if at all; and / or it could affect the economics aircraft operation. Aero fix might not sell so well, MCAS fix might require extensive PR / discount to improve sales, but does not guarantee commercial success.

As you note, a key parameter is public opinion. Historically, adverse perceptions fade or can be ‘adjusted’ - e.g. power of fake news, but the depth of feeling in this instance is unknown. Overseas operators, not on US soil, might be easier to dispel than would a home grown accident, but - the unknown effects of home certification error and poor oversight.

Beware the fickle human. Aviation safety has ranged from the domination of technical failure, through human ‘error’, to systems views, where in the widest sense the public within the ‘system’ has an input via media and politics.

It would be unfair to make a direct comparison with the demise of turboprops in the US regions. It happened, perhaps without great fanfare or body count, but it changed the operational industry and over time the marketing of newer types - the power of commerce, money talks.

If MCAS mods are approved, which appears likely, then why spend money on Aero fixes, but if other problems dominate - trim, then aero fixes could address both issues. Expensive and time consuming; requires balance, but as yet perhaps not Boeing’s call.
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Old 8th Jun 2019, 18:30
  #234 (permalink)  
 
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Smythe, et al.
There was no need to change the basic MCAS algorithm. It was ‘tried and tested’, and certificated.
The safety issue involved the integrity of the AoA input to the computation, where an error resulted in unanticipated trim operation due to weaknesses in the implementation - design good, engineering and certification not so.
Tried and tested...certificated??? You are posting in jest, no? Such a simple fix, yet so far 87 days on the ground?

From 0.6 to 2.5 without notifying the FAA? What was tested? Test pilots dont appear to have tested 2.5?

What about the low speed stall, push the nose down 2.5 degrees at low speed, and presumably low altitudes?

High G issues? push the nose down 2.5 degrees on a high G manuever?

It is not that one of the AoA sensors failed, look at how they are wired. They are not coupled to a single source, each one is wired to different sources. That is a rewire, not just a software issue.

How do you explain the certification process with EASA and the FAA used MCAS at 0.6, and never revealed the 2.5 change to the regulators? The AoA light on disagree doesnt work? ooops. In reality, if 2 sensors disagree, well then, what, pick one you like? (while the ac is nosing down because it thinks its stalling...

all
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Old 8th Jun 2019, 20:11
  #235 (permalink)  
 
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As they all have troubles with these lqtest generation engines.
I wonder really on a 737 flight how much it saves between a stansted to barcelona flight. The only thing you read is that they are more efficient so how much more ?
I live under a flight path in belgium well not actually the flight path , but just because they are not allowed to fly over brussel that much the take off to the south and then head west and then fly around brussel to go east again to germany for example.
But I checked the noise and an old 747f doesnt make more noise then a 787 while the 787 was on a shorter trip then the 747f so the super new engines dont really do much in the improvement of noise.
So i am curious if the the leap engine compare to the old CFM56 engine really makes so much up in fuel efficiency or this is just some guy with excel sheets.
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Old 8th Jun 2019, 20:54
  #236 (permalink)  
 
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I wonder really on a 737 flight how much it saves between a stansted to barcelona flight. The only thing you read is that they are more efficient so how much more ?
On the A320 (same engine with a slightly larger fan) the burns are around 15% down on the V2500 version, over the course of a year that is a lot of fuel.
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Old 8th Jun 2019, 21:24
  #237 (permalink)  
 
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The Max burns a little over 2000 KG an hour. Approx the same as the E190, but with 70 or so extra passengers.

On a 5 hour flight you should save approx 2500 to 3500 KG of fuel over a CFM56. It is pretty amazing how engine efficiency has changed in the last 20 yrs.

High G issues? push the nose down 2.5 degrees on a high G manuever?
According to the information I have the MCAS will still only trim .67 units for the high speed (high G) increasing AOA. The 2.5 was the mod for low speed to create the necessary stick pressures. .67 still worked for high speed, but it needed to be adapted. Ooops.

Tuff
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Old 8th Jun 2019, 21:47
  #238 (permalink)  
 
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Did anybody properly "preserve" their aircraft?
Where all fluids drained and purged?
Time to start thinking about "long term storage procedures" and how to "preserve" those aircraft.

Non flying aircraft also collect moisture in the strangest places so also start thinking about corrosion inspections.

On the same level; Is there an approved "return to flight status" procedure??

Just some thoughts worth thinking about, because this is not the end, it is just the beginning of the troubles.
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Old 8th Jun 2019, 21:54
  #239 (permalink)  
 
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Smythe, # 234
MCAS in normal operation worked exactly as designed; the system and design description appeared to meet the certification requirements. The AoA ‘failure’ was either not considered in the design, or judged insignificant in the failure effects analysis, thus it might never have been tested, ground or air. Theory and practice may have disagreed, but how can we tell.

0.6 to 2.5 appears to be a simple error; this might have been one of the self certification items without specific ground rig measurements, only software validation.

You appear to overlook that flight tests are not ‘stick free’, so the aircraft will not pitch unless the pilot fails to resist the change of stick force - change in force was the primary objective in the particular conditions. So during flight testing the difference in trim rate over time, opposed to absolute tail angle, would be perceived as a difference in stick force, except there was no lower value for comparison. The pilot would feel a change in force, and that the change (larger than necessary), meet the certification stability requirements which was the objective of MCAS.
MCAS involves stability (stick force); whereas approach to the stall 1.1 Vs is alerted with stick shake - not to be confused with the AoA failure in the accidents which generated a false stick-shake, and the stability certification requirements above 1.1 Vs, similarly comments re stalling Vs; (aircraft don’t think).

EASA generally validates FAA certifications - bilateral agreement, but can intervene at any level including flight tests; e.g NG question about trim.

Re AoA Disagree; see Boeing statement https://boeing.mediaroom.com/news-re...ts?item=130431.
The alert alone is meaningless, has no value in determining failure or action, and even without any drill would only be relevant to the optional installation of the AoA indicators (not fitted).
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Old 8th Jun 2019, 21:55
  #240 (permalink)  
 
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Does anyone, anywhere have any idea when the Max will return to service?
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