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Confusion about PSE vs FCS for secondary structure.

Confusion about PSE vs FCS for secondary structure.

(OP)
Howdy all,

We are repairing a V2500 thrust reverser used on an Airbus A 319/320/321. In the A320 SRM the entire nacelle is indicated to be secondary structure on pages 5/6. In figure 23 Sheet 4 on page 72, and the key to figure 23 on page 73 it indicates that the trust reverser translating sleeve attachment is a principle structural element, and _not_ a fatigue critical structure. I'm am trying to figure out what I need to have a repair to some minor damage approved.

Is this primary structure?
  • The Venn diagram on page 2 has all principle structural elements as primary structure.
  • It also states any PSE is FCS, but then why have a key that has columns for PSE and FCS and mark the PSE but not the FCS?
Will I need DER approval for this repair?
Will I need a damage tolerance evaluation for this repair?
Am I the only one confused by this SRM?

The damage is a shallow wear grove on the T-hinge on the translating cowl. This is .005" to .010" deep on a structure that is ~.250 thick. This is minor by my estimate, and I want to blend and alodine the wear area and then coat with dry film lubricant.

Thanks for everyone's help.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

RE: Confusion about PSE vs FCS for secondary structure.

2
maybe Airbus are saying the thrust reverser is a critical piece of a system (like the H. Stab pitch actuator) and so a PSE but it (unlike the HSPA) is not subject to fatigue loads (which is a little "odd") or possibly not subject to a rigorous DTA ? The thrust reverser may be safety critical but not fatigue critical ??

I suspect that there are very limited rework limits provided in the SRM, and going beyond these is going to be very difficult to substantiate. Maybe the basis of analysis is a full scale test of a B/P system. If so, it'd be interesting to see how the OEM substantiates typical MRBs in production ??

I think i'd involve a DER, I'd also see what I can get from Airbus fleet support.

another day in paradise, or is paradise one day closer ?

RE: Confusion about PSE vs FCS for secondary structure.

Why dont you contact the nacelle OEM?

RE: Confusion about PSE vs FCS for secondary structure.

(OP)
I went with the nacelle OEM (Goodrich). The first part of their response is brief, and yes, a damage tolerance evaluation will need to be done. Thanks for your help.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

RE: Confusion about PSE vs FCS for secondary structure.

2
Several catastrophic aircraft accidents have been caused by inadvertent thrust reverser deployment [mechanical/structural malfunction] during takeoff or cruise.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

RE: Confusion about PSE vs FCS for secondary structure.

One consideration of whether a part needs to be treated as fracture critical is its level of operational fault tolerance. Typically, safety critical aircraft system parts that have no functional fault tolerance, even if they are not primary structures, are treated as fracture critical. This means the part is subjected to specific design and analysis procedures, careful manufacturing and QA procedures during production, and special inspection practices during service.

RE: Confusion about PSE vs FCS for secondary structure.

The only component that could be classified as damage tolerant PSE structure may be engine mounts, failure of those is catastrophic. But the rest of the nacelle is generally considered Secondary Structure, and for most parts fatigue checks are mandatory.

Aerospace Stress Analysis and FEA Courses
http://www.stressebook.com
Stressing Stresslessly!

RE: Confusion about PSE vs FCS for secondary structure.

engine mounts can be redundant, failure of a TR would probably be catastrophic too

another day in paradise, or is paradise one day closer ?

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