What the heck are Blow Out Doors? 14

[cmarinelli]

Hello everyone,

I'm reverse engineering a latch that is used on a "blow out" door of a turbine engine thrust reverser. I like to know exactly what the part's function is, but I'm stumped here. What exactly is the function of this blow out door? Does it simply alleviate an overpressure in the nacelle? Does it operate only in flight, or during thrust reverser actuation? I believe it is located aft of the thrust reverser air stream which makes me believe it is really intended to operate during flight.

Any ideas on this?

Thanks in Advance,
Chris Marinelli
Dynatech Aerospace

 

[MintJulep]

The OP was in reference to reverse engineering A LATCH on a cowling door. I think you are a bit on the melodramatic side here.

Melodramatic?

July 25, 2000
113 people in Concorde crash. The cause of the crash is suspected to be an unapproved thrust reverser part that fell off a DC-10 that took off before the Concorde.

February 24, 1989
9 passengers ejected from the cabin and lost at sea after a cargo door departed in flight. CONTRIBUTING
TO THE ACCIDENT WAS A DEFICIENCY IN THE DESIGN OF THE CARGO DOOR LOCKING MECHANISMS, WHICH MADE THEM SUSCEPTIBLE TO INSERVICE DAMAGE, AND
WHICH ALOWED THE DOOR TO BE UNATCHED, YET TO SHOW A PROPERLY LATCHED AND LOCKED POSITION
CONTRIBUTING
TO THE ACCIDENT WAS A DEFICIENCY IN THE DESIGN OF THE CARGO DOOR LOCKING MECHANISMS, WHICH MADE THEM SUSCEPTIBLE TO INSERVICE DAMAGE, AND
WHICH ALOWED THE DOOR TO BE UNATCHED, YET TO SHOW A PROPERLY LATCHED AND LOCKED POSITION


January 4, 1990
The number 3 engine of a Boeing 727 fell off in flight as a result of “soft body FOD” after maintenance crews neglected to install a seal in the toilet system.

June 1, 2000
Pilot killed in helicopter crash after an unapproved screw in fuel control unit fails.

Sorry, but I can't be so cavalier as to assume that just because a part has a common name like "latch", or is small, or is part of a non-critical system that it can't cause serious harm if it fails.

 

[FieldTeam]

I would think a TR opening in flight would cause quite a bit of concern for a flight crew!
I wonder why the OEM can not provide spares for this part....or is it that they want too much money to produce it? I've seen some very clever fixes that operators perform to get around spending what it costs to fly large aircraft....most ending in heartache and additional cost down the road.
On the other hand, there are very reliable PMA parts on the market that meet or exceed OEM specs. Not all original manufacturer components are reliable in themselves. This is why we have AD's, SB's, service letters and such. If cmarinelli is operating by regulations, he should be fine.

It wasn't like he was asking what a latch was....now THAT would have been scary!!

 

[WKTaylor]

Mintjulip… I have hesitated replying simply due to the way this thread is turning… but I think it is necessary to express a few more thoughts.

YES melodramatic is an excellent expression of Your way-over-reaction.

I’ve moved forward in my career by sticking my “neck-out” and making engineering decisions that have been implemented on real aircraft flown by real live humans. NOTE: I NEVER stick-out my neck-out blindly or stupidly… and lunge forward… I always open my eyes and engaged my engineering brain, FIRST... then proceed forward at a rational pace.

Engineers MUST make critical decisions using the best analytical tools and processes available at the time. The next step is to take ACTION to implement those decisions in a timely manner so that REAL hardware can fly. I have seen analytically skilled engineers, "freeze-up" due to fear and confusion, resulting in NO actions taken. Often, these folks are infused with negative "I can't do that" or "I don't have enough knowledge to do that" or "If something goes wrong... they will blame me" stuck in their brains. Skilled engineers MUST be capable of doing the possible with relative ease... and stretching-hard to work major real-world challenges to develop flight hardware. If we are NOT capable of doing the relatively simple work proposed by cmarinelli, we might as well call this a hobby… not a profession.

Bogus parts are a problem... but there are regulations and proceedures for keeping them OFF aircraft. Likewise there are proceedures to develop and utilize airworthy [approved] parts, from alternate sources by using good reverse engineering practices and and proven fabrication practices.

For every Case You cited above, OEM engineering and FAA approval had been granted.

In the cases of MAINTENANCE ERRORS cited, engineering involvement was hardly a factor: IE work was done improperly. NOTE: By definition, maintainers can ONLY work to approved technical data. NOTE: FAA approved engineers [DFR, Liaison, etc] have authority to generate (create) tech-data where no data currently exists… and/or alter approved design data… such as for alternate parts, materials, processes, repairs, maintenance procedures, etc… when rational/logical/justifiable, to keep aircraft flying.

In the cargo door failure cited: NO Alterations, NO deviations and NO "unapproved parts or repairs" were noted… just faulty design and poor operation/maintenance. Note: we learn from these hard lessons and march on…. or pack-up and give-in.

NOTE: The Concorde was an accident waiting to happen. The entire Concord accident report is available at the following website... so You can judge for Yourself:

http://www.bea-fr.org/anglaise/actualite/concorde-en.htm

This was a thorough report and: every aspect was considered and numerous "tough/hard" findings/conclusions were presented. Systemic complacency, in my opinion, was the PRIMARY cause for that accident. In that case there was a demonstrated weakness in the Concorde design for catastrophic tire failures and subsequent damage mitigation… as indicated by numerous prior incidents. OH Yeah… and there was a mandatory protocol for runway FOD inspection [by ground vehicle] just prior to Concorde take-off/landings, which was neglected by airport authorities [implemented due to known tire-failure issues]. European lawyers would love to presume the simple answer that You proposed, in order to deflect/reduce the blame [and liability] away from the Concorde designers, Air France, and Charles de Galle airport authorities... onto a “fat” American airline company [Continental].



Regards, Wil Taylor

 

[MintJulep]

WKTaylor,

Thank you for your insightful last post. This thread did take some interesting direction, but ultimately I think it has been a useful exercise.

I am willing to concede a bit on the melodrama, after all, the point of melodrama is to make a point. However I disagree about "way-over-reaction".

The initial post is quite disturbing (to me, and apparently some others) as it suggested the possibility that unapproved parts might be making their way into the supply chain. I have no regrets about raising the flag on that original post. Eventually it became clearer that the poster is most likely a legitimate manufacturing who is aware of and will follow the established procedures and regulations for producing non-OEM parts. Had that information been disclosed earlier this thread would have been much less "active".

If we all take nothing else out of this thread, perhaps we have learned that sometimes how and where a question is asked is important.

 

[monkeydog]

cmarinelli,
I have backed off comments on this thread based on what wktayor stated above. After you elaborated in this thread, I have to eat my words that were implied towards you. You apparently are doing the right thing, and just came on this web site to hopefully gain more insight on the design.
Anyone have salt and catsup?

 

[787tech]

Blow-out doors can be found in several areas of an aircraft, mainly in areas where there is a risc for a powered system failure.
Think of it as a pressure valve, its purpose to efectively "blow out" and in doing so preventing ar minimizing the damage to the aditional structures or engine by releasing pressure. Most common are in the engine cawling and some in the wing to body fairing.
Usually these are rather basic assemblies but their importance could not be understated. They are designed to fail in certain conditions thus making them too strong minimize their effectivenes.

 

[Sparweb]

Cmarinelli, et. al.,

Forgive me WKTaylor & MintJulep, but we've had enough philosophy for one thread, IMHO, and should just get on with the topic. So I'm going to share a secret with you; one that I haven't revealed before on the forum, but I just want to move things forward.

Overhaul shops are great places to visit to chat with the folks who work with this equipment daily. They know it inside and out. But the gleaming OH facility is only one stop on the journey. These guys also have junk bins that are pure diamond mines for inquisitive engineers looking for parts to reverse engineer. Get some tossed-out latches plus some of the other key parts of the system, if you can, and take them back to your office. Not only will you see how it works, but you'll also see why they FAIL. After all, they were thrown out for a reason...



Steven Fahey, CET

 

[Nigel]

I would rather ask a question and be a fool for 5 minutes that not ask and be a fool forever.

Come on people, have we never asked a question others think we should have an answer for? If it is a genuine question, and they are not students, give them the decency of answering it without ridiculing them.


Nigel Waterhouse B Eng (Hon's)
Can-Am Aerospace,LLC, Canadian Aircraft Certification Centre

http://www.canamaero.com

 

[rb1957]

g'day nigel,

see some of my earlier posts

 

[ckmns]

Hello, I work in a big company which conceives and makes reversers . If I understand the question, doors serve in case of high pressure and can open in flight. The cable which holds them serves for protecting hinges and openings of trapdoor.
I worked on the development of A380 and in particular on these trapdoors.
Cordialy

 

[harrisj]

There are two quite different facets to the original question.

First, there is condemnation because cmarinelli is designing a 'reversed engineering component'. That has implications for Intellectual Property Rights, for safety issues, for reliability and many other aspects. Maybe the company he works for should be criticised for this, maybe not - we don't have all the facts. But I doubt that the author embarked on this project without instruction from his management, who are the ones who make the decision. It may indeed be a bad decision.

In asking the technical question, cmarinelli is making a good engineering call. How can he undertake a design review without understanding the function? Why shouldn't he post the question on Eng-Tips? I expect he will have asked other sources as well as this. He's making the best he can of an awkward technical problem and should be commended for asking the question. Long live engineers with enquiring minds.

John

 

[drawoh]

harrisj,

I am trying to put myself in cmarinelli's shoes. I would not want to be responsible for designing a latch to be used on a mysterious airborne device. I would need to know...

What must it do?

What forces and other environmental conditions are applied to it?

Are there any safety concerns?

What regulations must be met by it?

What is wrong with the current latch that we must reverse engineer it?

Clear design requirements and specifications must come from the customer and the project manager. I cannot see now anybody on eng-tips can answer any of the above in sufficient detail.

JHG

 

[harrisj]

Yes, JHG, I agree with you.
I am suggesting (hoping) that cmarinelli is trying to find out all the facts you have suggested and a lot more besides. I would be appalled if he expects to find all the facts on eng-tips. But getting as much information and background on any design task is a good thing, and I commend him for asking the question.
Hopefully he will educate his management team by showing them this thread and alerting them to the minefield he's in. I don't know if he's a junior designer or the CEO (but assume he's nearer the former, in which case he may be in a difficult position with regard to his career). I would rather he asked the question than blundered on in ignorance.

Sparweb - the 'philosophy' of this design problem interests and concerns me (and, it appears, many others) as much as the technical solution to the problem. So I defend my right to comment on it. This is an open forum and we can all learn from each others' comments, views and questions.

John

 

[Sparweb]

Harris,
You're probably right, but I've already convinced myself that Mr. Marinelli knows what he's doing, and the philosophical discussion is in the way of answering the question. A thousand lines of text have been written, and only two are a direct response. A few dozen more suggest other means of finding info. The rest...

Fodder for a separate thread?

Steven Fahey, CET

 

[RPstress]

Re reverse engineering parts, while it should technically be possible to do so safely, care is obviously necassary. (Duh!) In the case of a latch, particularly a blow-out door latch, it must function correctly in a variety of environments. The original latch supplier should have done salt spray, dust and grit contamination, and many more tests and verified the latch still operates (opens) in the originally specified pressure range. The risk from a latch like this is that if it gets jammed up or too stiff, the cowling that it's a part of can be blown off in the event of a system (e.g. bleed air) pipe rupturing or a leak from the bypass duct. Of course, if it opens at too low a pressure the next ground inspection will find find it open, and then a more thorough inspection will be needed to see if some system leaked or blew. There are quite a lot of false positives from these sorts of doors.

I'm not sure how the tolerancing of the reverse-engineered part would be decided. How would you make a latch that operates in the original pressure range if that range is unknown? I guess this is a direct question for you, Chris. I'm assuming here that as you were unaware of the part's function you don't have the range of pressure for actuation.

-RP.

 

[gwolf]

Did anybody notice that the original poster dropped out a month ago?

)

 

[rb1957]

doesn't stop a good argument ... oops, discussion !

 

[mkholcomb]

blow out doors are a safty feature that relieve the spike pressure resulting from a 'burst duct' overpressure in the engine compartment. we actually designed one reverser without them in the hopes that the structure would 'burp' itself in the event of a burst duct. It is a very difficlt thing to analyize so we just put in a blow out door in most cases.

 

[EDCCorp]

Oye! Come on people! One of my professors used to say never assume because it makes an Ass out of you and me. Just because someone asks a question, never, ever assume they are trying to do things the wrong way! I am glad that there are those who have given Chris some positive feedback and advice. MIL specs and standards have lots of good information and insight regarding testing various components for environmental, strength, etc. issues which can help in reverse engineering components. The PMA (or in Canada here PDA) process is long and involved, especially for some parts because reverse engineering is not as simple as figuring out the size and making the part from something you think works (I.e. bogus parts), but it is demostrating to the FAA, Transport Canada, etc. that the part will meet the intended fuction of the part it is replacing, and in some instances showing that it exceeds the intended fuction of the part it is replacing (I.e. greater life). You cannot get a PMA or a PDA without showing this. Getting PMA or PDA approval does not make the parts bogus. While I know some people are scared by complex parts, there are some aircraft that do not have parts available for sale by the manufacturer and as a result, there are companies who have obtained PMA/PDA approval to supply replacement parts for these aircraft to keep them safe. If we ran away from hard challenge, maybe we should stick to pencil and paper, no lights, walking to work, no cars, no computers, no electricity, etc.! how is that for melodrama

 

[Boathouse]

When I moved from the OEM world to an owner/operator/OEM world, the thought of PMA parts scared the brownstuff out of me...what do they (PMA houses) know about how a fuel nozzle of vane works? Turns out quite a bit in reality. They have to qualify the part by either test and computation or by identicality to the feds and this is an involved process. Experience here has shown that the parts are superior in build/finish quality and so far have operated flawlessly - in fact, our OEM engine supplier sells us PMA "O" rings when their part numbers are no longer available!

Paradigm shifts are a bugger aren't they??