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transaeroyyz
Topic Author
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Lauda 004 Questions

Sun Apr 17, 2011 12:26 am

"crashed due to a thrust reverser deployment of the number 1 engine in flight"
My question is aren't the engines supposed to snap off if large irregular loads are applied on them?

"Aviation writer Macarthur Job has noted that, "had that Boeing 767 been of an earlier version of the type, fitted with engines that were mechanically rather than electronically controlled, then that accident could not have happened." [2]
The incident led Boeing to modify the thrust reverser system to prevent similar occurrences.
What was the actual modification?
 
oldtimer
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RE: Lauda 004 Questions

Sun Apr 17, 2011 7:36 am

Quoting transaeroyyz (Thread starter):

"Aviation writer Macarthur Job has noted that, "had that Boeing 767 been of an earlier version of the type, fitted with engines that were mechanically rather than electronically controlled, then that accident could not have happened." [2]
The incident led Boeing to modify the thrust reverser system to prevent similar occurrences.
What was the actual modification?

As you obviously read the wiki report, just read the aircraft accident report as well, which is in the addendum and your questions will be answered.

As to you first question, the loads are somewhat different on a reverser deployed in flight at 0.78 mach, due to lots of strange aerodynamics that I do not fully understand, but its there in the accident report as well.

oldtimer
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tdscanuck
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RE: Lauda 004 Questions

Sun Apr 17, 2011 2:02 pm

Quoting transaeroyyz (Thread starter):
My question is aren't the engines supposed to snap off if large irregular loads are applied on them?

Yes. But reverse thrust is not a "large irregular load", it's a design load that the engine is supposed to withstand on every cycle.

Quoting transaeroyyz (Thread starter):
"Aviation writer Macarthur Job has noted that, "had that Boeing 767 been of an earlier version of the type, fitted with engines that were mechanically rather than electronically controlled, then that accident could not have happened." [2]
The incident led Boeing to modify the thrust reverser system to prevent similar occurrences.
What was the actual modification?

Sync locks. There is a synchronizer shaft between the T/R actuators that keeps them moving at the the same speed (prevents racking the T/R while it's in transit). The sync-lock is an electromechanical lock on one end of the sync shaft. In order to deploy the T/R the hydraulic module has to send hydraulic fluid the right direction *and* the sync lock has to release. The control loops are completely separate so inadvertent T/R failure now requires dual independent failures.

In a sense, it's actually three failures because the hydraulic control modules are internally dual-redundant (two valves have to actuator to deploy the T/R).

Tom.
 
transaeroyyz
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RE: Lauda 004 Questions

Sun Apr 17, 2011 3:52 pm

Quoting tdscanuck (Reply 2):
reverse thrust is not a "large irregular load", it's a design load

but even at 800 km/h? that must be a incredible force
 
tdscanuck
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RE: Lauda 004 Questions

Sun Apr 17, 2011 11:37 pm

Quoting transaeroyyz (Reply 3):
but even at 800 km/h? that must be a incredible force

Thrust drops off with altitude. The engine can't generate as much reverse thrust at altitude as it can on the runway, same as with normal thrust. There would be extra drag from the exposed cascade vanes, but that's not particularly large compared to magnitude of the thrust.

Tom.
 
transaeroyyz
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RE: Lauda 004 Questions

Mon Apr 18, 2011 12:33 am

why couldnt they recover from stall, restow the reverser, apply stall recovery techniques
 
474218
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RE: Lauda 004 Questions

Mon Apr 18, 2011 2:23 am

Quoting tdscanuck (Reply 2):
Yes.

Seems to differ with the FAR?

25.361 Engine Torque
.....

(b) For turbine engine installations, the engine mounts and supporting structure must be designed to withstand each of the following:

(1) A limit engine torque load imposed by sudden engine stoppage due to malfunction or structural failure (such as compressor jamming).

(2) A limit engine torque load imposed by the maximum acceleration of the engine.
 
vikkyvik
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RE: Lauda 004 Questions

Mon Apr 18, 2011 2:44 am

Quoting 474218 (Reply 6):
25.361 Engine Torque
.....

(b) For turbine engine installations, the engine mounts and supporting structure must be designed to withstand each of the following:

(1) A limit engine torque load imposed by sudden engine stoppage due to malfunction or structural failure (such as compressor jamming).

(2) A limit engine torque load imposed by the maximum acceleration of the engine.

My immediate question would be: are those irregular loads?

Basically, they are loads that the engine already has to withstand, but just maximized in this case. I don't think they would warrant an engine breaking off. But I'm no expert  
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".
 
Okie
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RE: Lauda 004 Questions

Mon Apr 18, 2011 2:53 am

Quoting transaeroyyz (Reply 5):

why couldnt they recover from stall, restow the reverser, apply stall recovery techniques


The simple answer would be that they did not recognize exactly what the problem was nor had time to respond.
When you are cruising horizontal at .8 mach and all the sudden are travelling vertical at .8 mach you only have only a seconds to respond before finding terra firma. It is pretty easy after the fact to determine what the issue was and to throttle the engine back until the reverser was restowed. The concept was that the reverser could be deployed in flight was so remote that one would assume that was probably one of the last things that would cross the pilots mind was reverser deployment.

Okie
 
tdscanuck
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RE: Lauda 004 Questions

Mon Apr 18, 2011 4:21 am

Quoting transaeroyyz (Reply 5):
why couldnt they recover from stall, restow the reverser, apply stall recovery techniques

They went into what was essentially a snap roll, followed by an extreme drive. The reverser destroyed lift on one wing...this is the same thing that flips DC-10's over when they do a hard landing on one gear. That sort of loading would pretty rapidly overstress the aircraft.

Quoting okie (Reply 8):
It is pretty easy after the fact to determine what the issue was and to throttle the engine back until the reverser was restowed.

The engines was already headed for idle (this is an automatic engine response to a t/r deployment). The issue was that the engine was so big that it took more time to spool down than the t/r took to deploy, so it was still making significant thrust when the reverser deployed. Thanks to interlocks in the thrust levers, you can't command a t/r to deploy without the thrust levers being at idle. This was a previously unanticipated risk since you don't have this long-spool-down time with low-bypass engines.

Tom.
 
474218
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RE: Lauda 004 Questions

Mon Apr 18, 2011 1:10 pm

Quoting vikkyvik (Reply 7):
My immediate question would be: are those irregular loads?

Basically, they are loads that the engine already has to withstand, but just maximized in this case. I don't think they would warrant an engine breaking off. But I'm no expert

I am no expert either, but I can read: This section seems to back up the fact that engines are not designed to fall off:

Subpart B--Design and Construction; General

Sec. 33.23

Engine mounting attachments and structure.

[(a) The maximum allowable limit and ultimate loads for engine mounting attachments and related engine structure must be specified.
(b) The engine mounting attachments and related engine structure must be able to withstand--
(1) The specified limit loads without permanent deformation; and
(2) The specified ultimate loads without failure, but may exhibit permanent deformation.]
 
tdscanuck
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RE: Lauda 004 Questions

Mon Apr 18, 2011 1:46 pm

Quoting 474218 (Reply 10):
This section seems to back up the fact that engines are not designed to fall off:

They are designed to fall off...that's why the pins in the engine mounts are called "fuse pins." But the FAR you're quoting doesn't say they're not designed to fall off, just that they can't fall off up to ultimate load. Ultimate load is 50% above the largest load you should be capable of seeing in service (by definition, the limit load). For obvious reasons, the thing the engine is attached to (the wing) must also withstand ultimate load without failure.

The whole issue of mechanically fusing the engines is for loads *above* ultimate load (an in-flight T/R deployment, by itself, shouldn't be above ultimate load). If you go above ultimate load, something is going to break. The fusing is there to make sure it's the pylon and not the wing that breaks.

Tom.
 
474218
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RE: Lauda 004 Questions

Mon Apr 18, 2011 2:38 pm

Quoting tdscanuck (Reply 11):
They are designed to fall off...that's why the pins in the engine mounts are called "fuse pins."



While Boeing may use "fuse pins" you can not make a "blanket statement that pylons are designed to fall off".

Lockheed did not use "fuse pins" on the L-1011.

McDonnell Douglas did not use "fuse pins" on the DC-10 or MD-11.

I would guess Boeing uses "fuse pins" because they can't meet the FAR's

Its like Boeing and "vortex generators" rather than designing a wing properly they correct their mistakes with "vortex generators.
 
yeelep
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RE: Lauda 004 Questions

Tue Apr 19, 2011 12:26 am

Quoting 474218 (Reply 10):
I am no expert either, but I can read: This section seems to back up the fact that engines are not designed to fall off:

You may be able to read, but still have an issue with comprehension. Nothing in that section of the FARs would preclude the implementation of a strut design that would separate from the wing when ultimate loads have being exceeded.

FAR 25.901 Subpart E powerplant general.

(c) For each powerplant and auxiliary power unit installation, it must be established that no single failure or malfunction or probable combination of failures will jeopardize the safe operation of the airplane except that the failure of structural elements need not be considered if the probability of such failure is extremely remote.

The key word above is need. It seems that manufactures have a choice when designing the strut wing interface based on differing design philosophies.

Quoting 474218 (Reply 12):
I would guess Boeing uses "fuse pins" because they can't meet the FAR's

You guess wrong.
 
tdscanuck
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RE: Lauda 004 Questions

Tue Apr 19, 2011 12:32 am

Quoting 474218 (Reply 12):
While Boeing may use "fuse pins" you can not make a "blanket statement that pylons are designed to fall off".

The alternative is to tear open the wing in a crash...how is this a better outcome?

Quoting 474218 (Reply 12):
Lockheed did not use "fuse pins" on the L-1011.

McDonnell Douglas did not use "fuse pins" on the DC-10 or MD-11.

Are you saying they didn't use fused mounts, or that they didn't use parts specifically called "fuse pins"?

Quoting 474218 (Reply 12):
I would guess Boeing uses "fuse pins" because they can't meet the FAR's

How on earth did you conclude they can't meet the FAR's? All the mounts from all the OEM's meet the FARs. The FAR says you have to take ultimate load without failure. They all do that. Fusing, by whatever mechanism, is only relevant for *beyond* ultimate load cases. All structures will fail somewhere beyond ultimate load...fusing is just a technique to control how it fails. You're way outside the FARs before fuse pins ever come into play.

Quoting 474218 (Reply 12):
Its like Boeing and "vortex generators" rather than designing a wing properly they correct their mistakes with "vortex generators.

Except their last two wings had vortex generators designed in from the beginning so it's impossible that they're corrections for mistakes.

Tom.
 
474218
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RE: Lauda 004 Questions

Tue Apr 19, 2011 2:39 am

Quoting tdscanuck (Reply 14):
Are you saying they didn't use fused mounts, or that they didn't use parts specifically called "fuse pins"?


The L-1011 pylon attaches to the wing mounted attach fittings with five (5) bolts.

The two main attach bolts are 2 1/2" in diameter. The two (2) forward drag strut bolts are 1 3/4" in diameter. The aft drag strut bolt is 2 1/4" in diameter.

All five (5) bolts are made from either H-11 Steel or 13-8 CRES, depending upon the build date.

The pylon attach fittings are attached to the wing structure using H-11 Steel Hi Tigues and close tolerance bolts. The engines mount to the pylon with eight (8) INCO 718 steel bolts.

Sorry but there are just no "fuse pins".

Quoting tdscanuck (Reply 14):
Except their last two wings had vortex generators designed in from the beginning so it's impossible that they're corrections for mistakes.


I find that hard to believe. If Lockheed can design a wing without vortex generators, you would think Boeing could too, if they tried.
 
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notaxonrotax
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RE: Lauda 004 Questions

Tue Apr 19, 2011 3:52 am

Quoting 474218 (Reply 15):

I find that hard to believe. If Lockheed can design a wing without vortex generators, you would think Boeing could too, if they tried.

What if having a certain design wing with Vortex Generators gives you the performance you want, what is the problem with that?

I agree, retro-fitting them on a brand new aircraft-type would imply a design-flaw of some kind, but what if Boeing decides that a few strategic Vortex Generators on the 787 / 797 - wing gives them the aerodynamic parameters they are looking for……..I don´t think we are talking about an "incorrect design", am I wrong?

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tdscanuck
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RE: Lauda 004 Questions

Tue Apr 19, 2011 4:26 am

Quoting 474218 (Reply 15):
The L-1011 pylon attaches to the wing mounted attach fittings with five (5) bolts.

The two main attach bolts are 2 1/2" in diameter. The two (2) forward drag strut bolts are 1 3/4" in diameter. The aft drag strut bolt is 2 1/4" in diameter.

All five (5) bolts are made from either H-11 Steel or 13-8 CRES, depending upon the build date.

The pylon attach fittings are attached to the wing structure using H-11 Steel Hi Tigues and close tolerance bolts. The engines mount to the pylon with eight (8) INCO 718 steel bolts.

Sorry but there are just no "fuse pins".

Makes sense to me, I'm not very familiar with the L-1011. Although the size and material doesn't tell you much...a 747 fuse pin is about 3" in diameter and very high spec steel. It's only called a fuse pin because, by design, it's got the lowest margin in the system so that's where the failure should occur.

Did Lockheed intentionally design the lowest margin point of the mount to be one so that the pylon will separate without tearing open the wing box, or did they just hope it wouldn't come up?

Quoting 474218 (Reply 15):
Quoting tdscanuck (Reply 14):
Except their last two wings had vortex generators designed in from the beginning so it's impossible that they're corrections for mistakes.

I find that hard to believe.

You're welcome to find it as hard to believe as you like, but it's true. And, in the words of Levar Burton, don't take my word for it: it already got discussed on a.net with OldAeroGuy, who actually helped design those wings. In a thread that you participated in. B777-200 Wing, White Squares? (by readytotaxi Feb 11 2010 in Tech Ops). The specific part you're looking for is Reply 34.

Quoting 474218 (Reply 15):
If Lockheed can design a wing without vortex generators, you would think Boeing could too, if they tried.

Of course they can...you seem to be under the incorrect belief that a wing without VG's is automatically better than a wing with them. It just ain't so. If the wing with them achieves the required performance and is some combination of lighter/less draggy/cheaper/easier to build then, by definition, it's a better design.

Tom.
 
vikkyvik
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RE: Lauda 004 Questions

Tue Apr 19, 2011 5:55 pm

Quoting 474218 (Reply 15):

I find that hard to believe. If Lockheed can design a wing without vortex generators, you would think Boeing could too, if they tried.

That's sort of like saying "if Boeing could design a medium-range airplane without an engine in the tail, you would think Lockheed could too."

It's completely ignorant of whatever design and performance specs/compromises went into the decision.
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".
 
Chamonix
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RE: Lauda 004 Questions

Fri May 13, 2011 8:56 pm

 
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jetmech
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RE: Lauda 004 Questions

Sat May 14, 2011 2:22 am

Quoting tdscanuck (Reply 4):
Thrust drops off with altitude.

Just to add to Tds's post. GE / P&W state that the GP7270 has a takeoff thrust of 70,000 lbs, dropping to 12,633 lbs at 35,000ft / M 0.85 (under ISA conditions). The GP7277 has a takeoff thrust of 77,000 lbs, dropping to 13,700 lbs at 35,000ft / M0.85 (under ISA conditions).

http://www.enginealliance.com/gpspec.html

I'm really not sure if we can assume a similar result for reverse thrust, but it does provide some idea of the reduction in thrust at altitude.

Regards, JetMech
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YokoTsuno
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RE: Lauda 004 Questions

Sat May 14, 2011 6:24 am

Quoting tdscanuck (Reply 9):
They went into what was essentially a snap roll, followed by an extreme drive. The reverser destroyed lift on one wing...this is the same thing that flips DC-10's over when they do a hard landing on one gear. That sort of loading would pretty rapidly overstress the aircraft.

Assuming they would have been able to switch the problem engine off would that plane have been flyable? If so, is this T/R just "a bit of extra" drag, like a deployed landing gear, or is there more to it?
 
DH106
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RE: Lauda 004 Questions

Sat May 14, 2011 10:06 am

Quoting YokoTsuno (Reply 21):
Assuming they would have been able to switch the problem engine off would that plane have been flyable?

The reverser caused an initial gross upset, but no actual structural or systems damage. The reason for the loss was that the upset rapidly placed the 767 in a highly 'unusual attitude', rapidly heading through Vne with stresses & G forces building up. Diagnosis & recovery time was extremely limited - if any at all.
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tdscanuck
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RE: Lauda 004 Questions

Sat May 14, 2011 12:29 pm

Quoting YokoTsuno (Reply 21):

Assuming they would have been able to switch the problem engine off would that plane have been flyable?

Yes, but there wasn't enough time for them to realize what was happening before it was too late. As dh106 said:

Quoting dh106 (Reply 22):
Diagnosis & recovery time was extremely limited - if any at all.

If, for some reason, the engine was at idle or off when the T/R deployed, they'd have been in trouble but probably survivable. But there was no way for the flight crew to know it was coming.

Quoting YokoTsuno (Reply 21):
If so, is this T/R just "a bit of extra" drag, like a deployed landing gear, or is there more to it?

With the engine at idle or off, it's a bunch of extra drag but probably manageable. With the engine running at thrust, it was a huge amount of extra drag *and* a huge disruption of airflow over the wing.

Tom.
 
Tod
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RE: Lauda 004 Questions

Tue May 24, 2011 2:02 pm

Is seems odd that nobody ever mentions that this airframe was one of the 763ER prototype and got put to the task pretty robustly before being converted into a customer product.
 
bueb0g
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RE: Lauda 004 Questions

Tue May 24, 2011 3:02 pm

Quoting transaeroyyz (Reply 5):
why couldnt they recover from stall, restow the reverser, apply stall recovery techniques

Because the tail fin failed within 6 seconds!
Roger roger, what's our vector, victor?
 
Viscount724
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RE: Lauda 004 Questions

Fri May 27, 2011 6:25 am

Quoting Tod (Reply 24):
Is seems odd that nobody ever mentions that this airframe was one of the 763ER prototype and got put to the task pretty robustly before being converted into a customer product.

That's not correct, The aircraft involved in the accident was OE-LAV, the 53rd 763ER built. It's strange that there are no photos of that aircraft in the A.net database.

The one you are referring to was the 2nd 763ER built (and the first with P&W engines). That aircraft is still flying today for US charter carrier Ryan International. After Lauda it spent a few years with UK charter carrier XL Airways until they went bust.


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AustrianZRH
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RE: Lauda 004 Questions

Fri May 27, 2011 1:29 pm

Quoting okie (Reply 8):
The concept was that the reverser could be deployed in flight was so remote that one would assume that was probably one of the last things that would cross the pilots mind was reverser deployment.

I think, probably not, as the first thing when the accident unfolded one of the flight crew said was:
23.30:37 FO: Ah, reverser's deployed.
So they identified the problem very quickly.
WARNING! The post above should be taken with a grain of salt! Furthermore, it may be slightly biased towards A.
 
Tod
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RE: Lauda 004 Questions

Fri May 27, 2011 2:34 pm

Quoting Viscount724 (Reply 26):
Quoting Tod (Reply 24):Is seems odd that nobody ever mentions that this airframe was one of the 763ER prototype and got put to the task pretty robustly before being converted into a customer product.

That's not correct, The aircraft involved in the accident was OE-LAV, the 53rd 763ER built. It's strange that there are no photos of that aircraft in the A.net database.

The one you are referring to was the 2nd 763ER built (and the first with P&W engines). That aircraft is still flying today for US charter carrier Ryan International. After Lauda it spent a few years with UK charter carrier XL Airways until they went bust.

Thank you for the correction.
I mistakenly was considering serial number 23765, Boeing effectivity VL-011.
Converted to customer plane by the 767 Special Interiors Task Force somewhere around 1988.
Sorry
Tod

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