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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 29th Jul 2019, 18:20
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Originally Posted by SamYeager
I doubt that Panorama will be overly favourable to Boeing's cause, the title's a clue, but it will be interesting to hear how accurate it is and whether anything particularly new comes out. I doubt there will be much, if anything, new personally.
It appears the BBC Panorama Team has borrowed the headline writer from the Daily Mail.
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Old 29th Jul 2019, 18:23
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Originally Posted by infrequentflyer789
I think (if I understand tdracer right) this particular risk analysis is for debris from one engine impacting the other engine - if it has enough energy to go through the engine and take out the FADEC then both engines are toast anyway, but if it only has enough energy to get to the inboard side and do a little damage, it might be better if it didn't hit the FADEC. But not, in the end, better enough to justify building left and right engines.
Thank you infrequent - that's exactly what I meant. If debris from one engine had enough energy to penetrate through the opposite engine to take out the FADEC or other engine critical system, it didn't matter because the opposite engine was already dead.
You can protect for low energy debris - blade fragments and the like. But when you start talking 1/3rd disc from an engine operating at high power, it's simply not feasible. You're talking inches of armor plate to do any good (and you can't assume a perfect tangential trajectory - I think the range was 5 degrees for high energy debris - so you need to protect a rather large area). I used to work with a couple guys that had worked in the old Boeing turbine division (that's right, Boeing used to make small turbine engines back in the 1960s) that showed me pictures of the damage to their test cell due to a rotor burst - went through armor plate and a brick wall - and that was just a little APU sized turbine.
I'm surprised the FAA allowed their personnel to be quoted in that NYT article (or even talk to the press - even off the record) - particularly during an active investigation. However I knew and worked with at least one of the quoted FAA engineers and I wasn't impressed - classic paper pushing box checker who couldn't see the forest for the trees - couldn't judge if something was safe and compliant, only if they could check their box.
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Old 29th Jul 2019, 19:35
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Strangely enough the BBC Panorama team do have a very nasty well deserved reputation for stirring up hornets nests with the British Government -a recent example being the way Migrants from the Caribbean who came to the UK were treated by the British Government when Mrs May was in charge of the home Office -many were not given the legal rights they were legally entitled to and the Panorama Team were shown to be totally correct in their reporting ---history says that team have been a little too accurate in the past -so watch and make your own viewpoints
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Old 29th Jul 2019, 19:37
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Originally Posted by tdracer
You can protect for low energy debris - blade fragments and the like. But when you start talking 1/3rd disc from an engine operating at high power, it's simply not feasible. You're talking inches of armor plate to do any good (and you can't assume a perfect tangential trajectory - I think the range was 5 degrees for high energy debris - so you need to protect a rather large area). I used to work with a couple guys that had worked in the old Boeing turbine division (that's right, Boeing used to make small turbine engines back in the 1960s) that showed me pictures of the damage to their test cell due to a rotor burst - went through armor plate and a brick wall - and that was just a little APU sized turbine.
Probably yet more thread drift, for which apologies. But I recall that an industrial turbine (which really are not that different from their aircraft-mounted cousins, and in this case was a derivative for the 'other role') has a disk 'go' when in use on an oil rig. The disk fragment went through the entire oil rig, doing the "hot knife through butter" thing as it went, and disappeared off the side. How much equivalent armour plating it went through, who knows. But it hardly slowed down.
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Old 29th Jul 2019, 20:21
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Originally Posted by Dave Sharpe
Strangely enough the BBC Panorama team do have a very nasty well deserved reputation for stirring up hornets nests with the British Government -a recent example being the way Migrants from the Caribbean who came to the UK were treated by the British Government when Mrs May was in charge of the home Office -many were not given the legal rights they were legally entitled to and the Panorama Team were shown to be totally correct in their reporting ---history says that team have been a little too accurate in the past -so watch and make your own viewpoints
They had 30 minutes to get the basics over which they did reasonably well, and I suppose helped inform the SLF what the issue was all about. But absolutely nothing of real interest to anyone wanting a deeper understanding- apart from the comments by the ex Boeing engineer which have already been heavily trailed. Even his comments left me wanting more explanation as to the cost cutting/resource denying he was alluding to.

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Old 29th Jul 2019, 20:29
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Originally Posted by Gove N.T.
It appears the BBC Panorama Team has borrowed the headline writer from the Daily Mail.
Seems quite accurate, they are planes, and they kill people, 339 so far . . . I suppose you would have the same attitude if your family had been killed on one ? . . . no ? . . . didn't think so . . .
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Old 29th Jul 2019, 20:44
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Thats a fair comment on the programme -but would the average Brit be interested in the more technical bits of what went wrong or what the pilots could have done in a better way-I-don't think the Panorama team did a bad job in the time they had -not a plank pilot but did fly rotary for a few years -
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Old 29th Jul 2019, 20:54
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The point you are all missing is it is one thing to get this old design flying again.

Another to convince the public to fly in it.

All those pictures of grounded Max’s will fuel massive renegotiations from potential buyers.

Remember how Lockerbie helped to bring about the end of PanAm?
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Old 29th Jul 2019, 20:54
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you mean this sub-thread, (which seems to live on even though it is insignificant in its contribution)

Relative to the engine Uncontained Hazard

The regulatory requirements treat this against a statistical threat, i.e. like weather, birs, ice, etal. its impossible to protect against all threats so it accepts a level of protection that history has demonstrated does not significantly contribute to risk of a catastrophic outcome compared to all other threats.in total

It basically looks at "lessons learned" (from history) and design protections that have worked in the past i.e. redundancy, separation and shielding.

Adding to the historical experience are some field tests of small fragment penetrations of actual aircraft structure to define residual energies and the liklihood of defeating the design protections.

The FAA typically take the most simplistic approach of determining compliance against their pocket lists of what is typically used in other designs, without any detailed analysis of energies, fragment sizes or shielding robustness. While the engine installer looks at a very complex analysis akin to what is used in the military to assess vulnerability against hazards in a hostile environment.

As I hinted in an earlier post, the B737max issue of larger overhanging engines threatening the aircraft from a vulnerability standpoint is burred in the minutiae and only dilutes the original thread subject
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Old 29th Jul 2019, 22:10
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[pax] Having just watched the BBC. Panorama programme about 'Boeings killer aeroplane' I wonder why can't the software be set such that the yoke has ultimate and overriding authority ? If the pilot wants something why not give it to him?
Mind you, in airbus vehicles, why can't the display show the side stick inputs from the other seat in case some one goes rogue.
Doesn't seem difficult to me.
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Old 29th Jul 2019, 22:31
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Are we not losing the plot here?
The possibility of an engine breakup seems to me an entirely different matter from the flight control failures that have killed more that 300 trusting passengers.
This thread deals mostly with the latter and there is a lot of serious issues to address. The engine issue perhaps deserves its own thread, but should not be allowed to become a red herring in this inquiry.
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Old 30th Jul 2019, 00:50
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Well, it really started as a result of the LEAP being moved, a factor common to both potential dangers.
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Old 30th Jul 2019, 00:59
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If the pilot wants something why not give it to him?
That is already the case.
The control column and elevator did not stop working.
More importantly use of the trim switches overrides MCAS and will return the aircraft to an in trim state.
Manual trim also overrides MCAS.
That is why on the flight before the Lionair crash the crew were able to maintain control and complete their flight. They used the available resources.
That is also why the flights stayed in the air for as long as they did. The aircraft was controllable but required significant control inputs which is daunting for crews who rely on the AP to operate the aircraft.
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Old 30th Jul 2019, 01:01
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It would seem to me that the root cause of the issues around the MAX are most obviously demonstrated with the rudder cable issue. The issue is black and white, the MAX does not meet certification standards.

So, the question is how was the decision made to grant a let from the certification requirements

What should be: ODA's demonstrate and document compliance with the certification standards. The regulator has to sign off on any deviation from those standards and they alone get to make the call

What was: ODA's decided that compliance was not necessary and the FAA said OK without any apparent review.

It is hard not to think that this is the culture that made something like the MCAS fiasco inevitable and now the genie is out of the bottle. It sure seems like the deeper people dig into how this aircraft got certified the uglier it gets

Here is something else to think about. How come it is OK that the MAX is the only in production airliner anywhere that does not have the capability of separating the Captains and Copilots control wheel/stick in the event of a control jam.

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Old 30th Jul 2019, 01:35
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Originally Posted by Loose rivets
Well, it really started as a result of the LEAP being moved, a factor common to both potential dangers.
No, the rotor burst risk did not change due to moving the engine forward - the rotor burst risk changed because the potential rotor burst debris got larger due to a larger diameter engine.

Big Pistons, did you read the NYT link? The ODA didn't approve rotor burst, the FAA manager did, overriding the concerns of some FAA personnel in the process.
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Old 30th Jul 2019, 01:39
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Originally Posted by Big Pistons Forever
How come it is OK that the MAX is the only in production airliner anywhere that does not have the capability of separating the Captains and Copilots control wheel/stick in the event of a control jam.
I beg to differ.
To date there has been no indication that the MAX was different from the NG in this respect.
Moreover the diagram in the interim reports do seem to indicate that the Captain and FO control columns actually separated.



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Old 30th Jul 2019, 02:30
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No, the rotor burst risk did not change due to moving the engine forward - the rotor burst risk changed because the potential rotor burst debris got larger due to a larger diameter engine.
Quite so, but the reason the thread drifted and indeed split, was I'd guess, the assumption of the cable vulnerability.
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Old 30th Jul 2019, 04:55
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Originally Posted by tdracer
No, the rotor burst risk did not change due to moving the engine forward - the rotor burst risk changed because the potential rotor burst debris got larger due to a larger diameter engine.

Big Pistons, did you read the NYT link? The ODA didn't approve rotor burst, the FAA manager did, overriding the concerns of some FAA personnel in the process.
The engine certification including containment is not dependent on the size of the engine, the outcome for the blade separation is constant. For a ruptured disk, history has shown that no design is able to be protected from the release of the disk, and no real protection exists beyond avoiding having disk failure. Control system redundancy is nice to have, no doubt, but the A380 burst was looking at a wing fire as much as any other outcome, in an aircraft that had redundancy, which was mostly lost from the destruction wreaked by a single failure...

SWA 1380 lost #13 fan blade on the CFM56-7B just outside of the dove tail. That liberation resulted in the subsequent failure of the nacelle, and liberated components of the nacelle caused the decompression and fatality of the passenger. The earlier SWA3472 liberated a blade forward of the the nacelle, and the nacelle was destroyed by the out of balance loads. As devastating as that outcome is, the fan blade was technically contained in both cases. Had a disk failed, then all bets are off, disk rupture usually results in 3 and occasionally 4 major sections of the disk being released, and each one has catastrophic kinetic energy levels, as in it doesn't matter what flavour the plane is, you don't want to be any where near it. The LEAP engine fan blade is required to be mitigated by the cowl, as the -7B was, a disk, is mitigated by clean living, religion and good maintenance inspections.

As frustrating as the MCAS shambles has been, and the manual trim issue, I would have thought that the manufacturer was justified in the position of the control issues notwithstanding queries by the FAA TAD that may have occurred.

The probability of a disk failure is expected to be an extremely remote event. The disruption of the rudder cable would require the part of the disk, (say 3 items liberated...) with about a 1' arc at about 20 radius hitting the cable/cable supports etc. that ends up being 3 x (1+1) /126 or about 5% likelihood of impact, if you assume that the release is able to be of 3 parts at the same time. The physics of the release don't permit that to be the case, they are released with a slight latency, which reduces the likelihood of a specific part being hit. The rough likelihood of hitting the rudder control is less than 5% on a liberation, between 1.5-3.5%... of an extremely remote initial failure.

The CFM 56 is approaching 1 billion hours of engine operation, and a liberated fan blade caused a single fatality in that time, and no failure of a rudder control has occurred from any disk failure. Halve that time for the aircraft flight hours, and it is still well outside of the area of interest as a risk factor for a certified design.

The rudder control has a risk from being severed by a meteor strike that would be similar levels of likelihood.

Assuming that a failure occurs, then the catastrophic outcome that has caused gnashing of teeth, wailing and renting of cloth is not certain to lead to a hull loss unless it occurs at high speed on a take off roll, and in the early stages of the takeoff flight path up to around V2 +40. Above that speed, control can be maintained effectively with aileron alone, but at the cost of an increased stall speed, well above a normal "in balanced flight" stall, due to the vagaries of yaw-sweep-spoiler rise and the resultant AOA increase required for a given flight path. (the "40kts" is the amount that the actual stall was increased in the RAAF B707 accident off Sale in the late 80's, where a double asymmetric demo was undertaken with rudder boost inhibited... the resultant roll rate was enough to throw an engine off the pylon). A disk failure surprisingly doesn't have a propensity to occur on a takeoff, they happen at idle, cruise, power reduction, and more or less anywhere the 600lb gorilla wants to sit, they are random in nature, and therefore the probability of their occurrence on any takeoff where a loss of a rudder control would then be catastrophic is a function of exposure alone, and that is about 0.25%-0.5% of the total flight time of the B737... multiply that by the overall likelihood, and the likelihood of a consequent rudder problem and you are much more likely to get taken out by the meteor.

I don't object to control systems that have redundant and separated control architecture, that is just good design practice particularly coming from a military background, but I don't think that amongst the other serious issues that have been raised that hysteria is helpful to successfully getting Bill Boeing back in the air with an adequate product that does a fair job for the industry.

The risk following a fan blade failure is that the stabiliser is severely damaged by the subsequent loss of the nacelle, shades of foam shedding on the SST.

Last edited by fdr; 30th Jul 2019 at 05:12.
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Old 30th Jul 2019, 07:03
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Originally Posted by tdracer
No, the rotor burst risk did not change due to moving the engine forward - the rotor burst risk changed because the potential rotor burst debris got larger due to a larger diameter engine.

Big Pistons, did you read the NYT link? The ODA didn't approve rotor burst, the FAA manager did, overriding the concerns of some FAA personnel in the process.
The FAA manager named in the article would have directed closure of the FAA issue paper that raised the concern about rudder cable protection. He would not have approved the rotor burst analysis.

Last edited by Dave Therhino; 30th Jul 2019 at 07:22.
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Old 30th Jul 2019, 09:36
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Remember how Lockerbie helped to bring about the end of PanAm?
But not the 747.
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