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What the heck are Blow Out Doors?
14

What the heck are Blow Out Doors?

What the heck are Blow Out Doors?

(OP)
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

RE: What the heck are Blow Out Doors?

Does this question scare the hell out of anyone else?

RE: What the heck are Blow Out Doors?

(To MintJulep)

Yes.

RE: What the heck are Blow Out Doors?

The question doesn't scare the hell out of me.  The fact that someone is reverse engineering a component (most likely for a passenger aircraft) without knowing the function or design intent of the component.
This probably happens all the time.

RE: What the heck are Blow Out Doors?

yeah, but is anyone going to be helpful ?  

chris, i'd suggest that you start with the airplane's maintenance manual, it should describe the detail function of the door.  failing that, possibly looking at the door and how it's attached to the plane will answer some questions ... if there're electrical sensors and systems around (prox. switches, actuators) it then there are going to be complex activation conditions; if there's just a simple mechanical system (a spring or an over-center mechanism) then there's probably only a very simple (over-pressure) activation.

good luck

RE: What the heck are Blow Out Doors?

(OP)
Gentlemen (except RB1957),

I apologize for not being born with an innate knowledge of all aircraft systems. We typically work on turbine engine components, but are branching out into other areas and trying to LEARN before we start Reverse Engineering. We've asked our airline contacts and haven't gotten a thoughtful response.

We don't make anything without thorough knowledge and complete testing of every component. We partner with companies that have expertise in particular types of components. I'm just trying to get a better understanding of the function of a blow out door other than the obvious.

I have looked at the location and operation of the component, and it has no sensors, actuators, or switches, merely a cable that limits the door opening. We are looking at one of the latches that has a definite break-away torque required to open the door provided by a cam/detent and spring loaded roller.

If you have something positive to add, please do. If you only have negative comments, please keep it to yourself so as not to stunt free and open discussion.

Chris Marinelli

RE: What the heck are Blow Out Doors?

I think that questioning the ability of someone designing aircraft components and asking dubious questions is very constructive.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: What the heck are Blow Out Doors?

Quote:

We don't make anything without thorough knowledge and complete testing of every component

Where does that "through knowledge" come from?  Internet forums?  The airlines?  The people who KNOW what this component does are the good people at GE, or Rolls Royce, or Pratt and Whittney that designed the engine.

How do you test a part if you don't know what it does or how it is supposed to perform?  Besides, "testing" proves nothing.  The Pinto was "tested", it still exploded if you ran into the back end because nobody ever though to test that particular situation.

Counterfiet aircraft components are a real problem.  Airplanes crash because of them.

I'm still scared.

Is that positive enough for you?

RE: What the heck are Blow Out Doors?

chris,

i'd try to get the component (airplane or engine) manufacturer's open source information (maintenance manuals in particular).  i suspect that the flap needs to be rigged in some way to control the opening pressure.

but it sounds like the flap is a simple mechnaical system (a simple input (over-pressure) and a simple response (opening the valve).

as to the other posters ... let them vent, it is their prerogative

good luck

RE: What the heck are Blow Out Doors?

So, why don't you go to the manufacturer and ask them?

RE: What the heck are Blow Out Doors?

just a thought, but i'd think that the manufacturer isn't going to reveal their hard earned technical data (secrets?) to someone planning on competing against them in the markerplace for replacement parts.

RE: What the heck are Blow Out Doors?

Quote (FAA):

Unapproved Part definition: A part, component, or material that has not been manufactured in accordance with the approval procedures in FAR § 21.305 or repaired in accordance with FAR Part 43; that may not conform to an approved type design; or may not conform to established industry or U.S. specifications (standard parts). Such unapproved parts may not be installed on a type certificated product, unless a determination of airworthiness can otherwise be made.

http://www.asy.faa.gov/safety_products/unapprovedparts.htm

http://www.faa.gov/avr/sups/standard.cfm

RE: What the heck are Blow Out Doors?

MintJulep,

consider the possibility that this is a part manufactured under a PMA.  the intention doesn't have to be misrepresentative or "counterfeit"; there are legitimate ways to manufacture approved parts.

RE: What the heck are Blow Out Doors?

> If you have something positive to add, please do. If you only have negative comments, please keep it to yourself so as not to stunt free and open discussion.

Don't agree.

Chris - this is a forum, where every opinion - negative or otherwise - counts for something and is encouraged. As long as it is relevant to the question it shouldn't matter. If what you're saying was true, then we would be saying to all of those junior/other engineers out there: "Oh, that's fine just go ahead and build your proposed design. I won't check it because I don't want to point out the negative aspects of your work." How many aircraft would fall out of the sky if we couldn't point of people's design shortcomings? Lots. Engineering is a critical business, if you don't like negative comments you should be in another industry.

Cheers,

-- drej --


------------
See FAQ569-1083 for details on how to make best use of Eng-Tips.com

RE: What the heck are Blow Out Doors?

rb1957,

I recognize that there are methods to gain approval of parts.

The original poster has provided no indication that he has such approval, or is even aware that approval processes exist.

RE: What the heck are Blow Out Doors?

6
cmarinelli

Recommend You get a copy of MIL-HDBK-115 “Reverse Engineering”. I think there is also a book with roughly the same title available thru bookstores. I found this document discusses many practical topics/issues/questions that might help You thru the initial engineering process leading to FAA certification.

Also recommend checking the FAA Advisory Circulars at the following website and searching on key-words “parts” and "certification” for appropriate documents relative to FAA certification issues. http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/MainFrame?OpenFrameSet

NOTE: I am assuming that this is for a civilian aircraft… otherwise military “certification” issues would likely be identified in appropriate “JSSG xxxxx” documents.  

For the rest of You Guys... MintJulip ...  soap-box time…

My favorite intro line(s) for many of the topics I’ve needed to discuss with experts [scientists, engineers, technicians, mechanics, nurses, lawyers, secretaries, waitresses, gardeners… whoever…”] has been:

"I have a dumb question for you"  
or
"I need to ask You a (few) REALLY dumb question(s)".  

Most folks tend to hear what I am asking [next] in a more-positive/relaxed way… ‘cause I am really saying: “help me understand this so I can be informed/guided by Your experiences”.  

If cmarinelli was a student “doing a homework problem”, or a non-engineer asking an “engineering 101” question, then I’d say “red-flag him and good riddance”.

HOWEVER, DO NOT denigrate a fellow engineer asking a “dumb question” like this. He appears to be a sincere, competent engineer asking a “dumb question” because he has a REAL need to understand what the function of a cowling blow-out door is, and any subsequent implications, so he can deal with it and do the assigned work, FAST. He may eventually realize it is too complex/subjective a topic and NOT worth pursuing… he but also he might gain appropriate insight and excel at this tasking.

I have been stuck in some pretty awkward positions [“challenges”] in my +26-yr career… and have had to dig to the root of a topic [problem] FAST to be effective. In doing so I have asked a pile of direct “dumb” questions and been given a gold-mine of understanding in return. OK, I try to do my homework in advance… but that has [undoubtedly] left me realizing what I really DO NOT know about the topic. That’s when I have turned to others asking “dumb questions”.

What amazes me about aero engineering is the relatively vast sum of knowledge out there that is NOT easily accessible or documented… but is available, IF You just know where to look. Getting a peek at a wide/unique variety of topics, thru the eyes of others, has been an invaluable starting point, and on-going practical training, for me.

As for taking on an engineering task in unfamiliar territory... as an old/famous [departed] aero engineer loved to say, when asked why he risked his career/fortune by designing a popular homebuilt aircraft...  “A turtle only makes progress when it’s neck is stuck out”.

Regards, Wil Taylor

RE: What the heck are Blow Out Doors?

Ok, my turn on the soap box.

Counterfeit parts are a real and serious issue.  That is why the FAA has an entire department dedicated to the subject.

Aircraft in flight are intolerant of engine failure.  There have been two recent crashes with fatailites in the New York City area that both appear to have engine failure as the initiating event in the crash.

The original poster may very well be a sincere and competent engineer, and the company that he purports to work for does actually appear to be a legitimate aerospace firm.  However, his responses to being challenged have not convineced me that he is aware of the existing requirements and processes for what he is attempting to do.

Furthermore, asking a "dumb question" on a topic with potential life-safety and legal implications in a public forum such as this does not serve the interests of the industry well.  If the poster is legitimate it certainly seems that he should have a better network of contacts to pose questions to than anynomous names on an internet forum.

Taking risks is easy when it's not your neck that is sticking out.

RE: What the heck are Blow Out Doors?

2
"Counterfeit parts are a real and serious issue."
This is true.

"Aircraft in flight are intolerant of engine failure."
This is not necessarily true. There are many situations where in flight shut downs occur safely.

"Furthermore, asking a "dumb question" on a topic with potential life-safety and legal implications in a public forum such as this does not serve the interests of the industry well. "
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. The OP was not looking to redesign the cowling or the door itself. If anything I think he is doing right by trying to understand the environment that the latch is operating in.

"However, his responses to being challenged have not convineced me that he is aware of the existing requirements and processes for what he is attempting to do."
I would assume that you are refering to his management and quality reps as well who also shoulder that burden.

"Besides, "testing" proves nothing."
That has got to be the most asinine statement I have ever heard. Bad or improper testing proves nothing. Testing is one of the most important things that can be done to assure safety and proper operation.

RE: What the heck are Blow Out Doors?

2
Mr. Marinelli seems to have been given a very narrowly defined problem.  Looking for the bigger picture was the right move, but he could have phrased the question better, and shouldn't have published the company name on his post.  I think he's subsequently made himself clear and we can now get on with the answer.

Firstly, which kind of TR is this stuff for?



                                                or



Since you're branching out into new areas, you could try visiting your "airline contacts" to visit their facilities and see the aircraft for yourself, on the ramp, in the shop, and in pieces on the table.

Steven Fahey, CET

RE: What the heck are Blow Out Doors?

(OP)
I must say I regret asking a question and starting this thread.

Thanks to rb1957, wktaylor, FredGarvin, and SparWeb for understanding why I might ask such a question.

My company has obtained many dozens of FAA-PMA's, and are mindful of FAA regulations governing certification of the same (Order 8110.42A, FAR 21.303, etc.). Our ACO has commended us on the professionalism and thoroughness of our PMA applications. We take flight safety very seriously, and know that lives potentially hang in the balance. Although PMA's may not be held in high regard, there are some out there that are doing what they're supposed to. It is up to the FAA to make sure everyone meets the same standard.

We use MIL-HDBK-115 as a template for our reverse engineering methodology as well as our experience developing (via R.E.) dozens of parts for the US Army, supported by 150 hour engine tests. We scrutinize and document the reasoning behind every dimension, fit, finish or process and perform a failure mode and effects study on every part, no matter how simple.

For every certification project we perform a preliminary design review to evaluate the feasibility of pursuing a particular PMA. Wktaylor hit it on the head in that I was trying to quickly obtain insight into an area I am not familiar with.

SparWeb is correct in that I am only interested in a Latch with a spring loaded cam/detent overpressure configuration. It is on a CF6 translating cowl TR which may very well be the lower picture of SparWeb's post. It is essentially a spring-loaded roller attached to a small bracket that rides on a cam with a notch. The roller 'cams out' of the notch when sufficient torque is applied.

I've visited OH shops in AirCanada and SW, and am scheduling a visit to Lufthansa and possibly Delta. Unfortunately, it is difficult to get significant time in the shop as the technicians need to get their work done.

Thanks again to everyone for sharing their two cents.

RE: What the heck are Blow Out Doors?

Quote (FredGarvin):

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.

RE: What the heck are Blow Out Doors?

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!!  

RE: What the heck are Blow Out Doors?

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

RE: What the heck are Blow Out Doors?

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.



RE: What the heck are Blow Out Doors?

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?

RE: What the heck are Blow Out Doors?

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.

RE: What the heck are Blow Out Doors?

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

RE: What the heck are Blow Out Doors?

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
www.canamaero.com

RE: What the heck are Blow Out Doors?

g'day nigel,

see some of my earlier posts

RE: What the heck are Blow Out Doors?

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

RE: What the heck are Blow Out Doors?

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

RE: What the heck are Blow Out Doors?

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

RE: What the heck are Blow Out Doors?

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

RE: What the heck are Blow Out Doors?

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

RE: What the heck are Blow Out Doors?

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.

RE: What the heck are Blow Out Doors?

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

)

RE: What the heck are Blow Out Doors?

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

RE: What the heck are Blow Out Doors?

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.

RE: What the heck are Blow Out Doors?

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

RE: What the heck are Blow Out Doors?

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??

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