Primary Airframe Structure?

[GDGR]

I've been rooting through POH, Maintenance Manuals, Service Manuals, but I have yet to find what I'm looking for...

I need to know whether Mooney classifies the vertical stab leading edge skins as primary structure??? 

Having the Skins removed, replaced this weekend, and my AME-S is wondering if he's going to require an AME-O sign off or not? 

TIA Everyone! This site has been a wealth of information. 

[KSMooniac]

Yes, that would be primary structure.

If you're who I think you are, good luck! I sent you pics of an empennage a couple evenings ago.

Sent from my LG-US996 using Tapatalk

[GDGR]

@KSMooniac much appreciated. It’ll be repaired either way this weekend. Just uncertain if it’ll need a second signature or not. 

[PT20J]

1 hour ago, KSMooniac said:

Yes, that would be primary structure.

Not necessarily disagreeing, but I’m curious why this would be. I believe FAA defines primary structure as structure carrying flight, ground or pressurization loads the failure of which would affect the structural integrity of the aircraft. Probably the same in Canada. Hard to see that the leading edge skin carries significant structural load. If it really matters, I’d ask Mooney. Or, maybe @M20Doc can weigh in. I’d be interested in his answer.

Skip

[GDGR]

Just now, PT20J said:

Not necessarily disagreeing, but I’m curious why this would be. I believe FAA defines primary structure as structure carrying flight, ground or pressurization loads the failure of which would affect the structural integrity of the aircraft. Probably the same in Canada. Hard to see that the leading edge skin carries significant structural load. If it really matters, I’d ask Mooney. Or, maybe @M20Doc can weigh in. I’d be interested in his answer.

Skip

The structural guy doing the skin repair is saying that it needs to be called out in the POH or Maintenance manual as a Primary Structure. I don’t see it anywhere in there. Either way, he’s got his AME-O ready and willing to sign off on it, so no big deal. 

I was more curious myself to see if anyone has seen it called out. 

[Guest]

There is no Structural Repair Manual for this airframe, the structures section references the AC43.13, you could contact Mooney to see what their definition of primary structure is.  

By the CARs definition you could argue that your S rated AME could make the repair.  If your S rated AME has an AMO willing to inspect and sign off the repair and it doesn’t add greatly to the cost I’d do it.  If your insurance company is paying for the repair they won’t question it.

Clarence

[GDGR]

And the answer straight from Mooney Engineering:

 

Yes - It is Primary Structure - Also you may want to check some other items:
Inspect the following:
1.        Check free play of empennage.
2.        Empennage and aft tailcone for deformity and sheared rivets.
3.        Stabilizer trim hinges, trim actuator brackets, trim actuator fitting at empennage, and attaching hardware.
4.        Hardware attaching top hinge brackets to tailcone.
5.        Rudder push/pull tubes.

 

[jaylw314]

15 hours ago, PT20J said:

Not necessarily disagreeing, but I’m curious why this would be. I believe FAA defines primary structure as structure carrying flight, ground or pressurization loads the failure of which would affect the structural integrity of the aircraft. Probably the same in Canada. Hard to see that the leading edge skin carries significant structural load. If it really matters, I’d ask Mooney. Or, maybe @M20Doc can weigh in. I’d be interested in his answer.

Skip

Wasn't there an accident where a commercial aircraft had a catastrophic loss of control and crashed after losing the leading edge skins on the horizontal stabilizer?  

[GDGR]

Showed a friend who flies my Mooney from time to time these photos. Told him, "Anyone who leads this DC-3 repair in the Antarctic, and can get the plane back home, is more than free to work on my Mooney!"

 

[PT20J]

3 hours ago, jaylw314 said:

Wasn't there an accident where a commercial aircraft had a catastrophic loss of control and crashed after losing the leading edge skins on the horizontal stabilizer?  

I don't know; I don't recall it. I do recall the Airbus that had the vertical stab come off after a rudder hard over doublet applied by the pilot flying. But my quest was just to understand the question in terms of the definition of primary structure. The aircraft manufacturer is the final authority and Mooney says it is primary structure, so that's the answer. I think this is an excellent example of a case where there can be a lot of opinions, but only one correct answer.

[GDGR]

Just now, PT20J said:

I don't know; I don't recall it. I do recall the Airbus that had the vertical stab come off after a rudder hard over doublet applied by the pilot flying. But my quest was just to understand the question in terms of the definition of primary structure. The aircraft manufacturer is the final authority and Mooney says it is primary structure, so that's the answer. I think this is an excellent example of a case where there can be a lot of opinions, but only one correct answer.

Precisely. My AME-S Buddy is willing to do the work, but wanted to know if he could sign off on his own (if it was not Primary), or required an AME-O to do that for him. 

As @M20Doc suggested, there isn't a structural manual for older Mooneys. Mooney did send me the copies for Structure and Stabilizers for the M20R, and stated it's more in depth and is also built the same way as the old ones. He followed up by asking engineering, and they confirmed it's Primary. 

As a primary structure, AME-O must sign off. Not a big deal, as he's under contract with one, and it will be done in accordance with Transport Canada Rules and Regulations. 

 

[jaylw314]

12 minutes ago, PT20J said:

I don't know; I don't recall it. I do recall the Airbus that had the vertical stab come off after a rudder hard over doublet applied by the pilot flying. But my quest was just to understand the question in terms of the definition of primary structure. The aircraft manufacturer is the final authority and Mooney says it is primary structure, so that's the answer. I think this is an excellent example of a case where there can be a lot of opinions, but only one correct answer.

Ah, found it...

https://en.wikipedia.org/wiki/Continental_Express_Flight_2574

From the NTSB report

"The failure of Continental Express maintenance and inspection personnel to adhere to proper maintenance and quality assurance procedures for the airplane's horizontal stabilizer de-ice boots that led to the sudden in-flight loss of the partially secured left horizontal stabilizer leading edge and the immediate severe nose-down pitchover and breakup of the airplane. Contributing to the cause of the accident was the failure of the Continental Express management to ensure compliance with the approved maintenance procedures, and the failure of FAA surveillance to detect and verify compliance with approved procedures."