T-6 Inspection for Airshow Aircraft

Ken · **Posted:** Sat May 05, 2012 7:39 pm

I've got a buddy with a nice T-6G. He is actively flying the airplane and enjoying it to the max. This has included some flying with the Aeroshell gang and pushing the airplane as hard as they do including snap rolls; certainly no Sunday driver.

Where are the weak points in this airplane that deserve extra inspection attention considering how it is being operated? I am confident that the airplane is being flown within its book limits, but its bones date back to 1941 and, of course, we don't know exactly how she was flown with her previous owner(s).

Any insight on items for walkaround inspection and/or items that can only be accessed during an annual-scale inspection would be appreciated. I want to see my buddy fly many safe & fun filled hours.

Thanks for the input,
Ken

bdk · **Joined:** Sun May 02, 2004 1:16 am **Posts:** 11281

Other than the attach angle AD which stems from a metal fatigue issue, my biggest concern would be corrosion. Look carefully in every access hole (a borescope would not be a bad idea in some areas). Some of the extrusions may be exfoliating in the wings and stabilizers. Probably the worst thing though is shoddy maintenance by civilian owners/stuff put together wrong.

I found a crack in my steel frame (the vertical member just above the uplock). The origin appeared to come from an undercut weld from the factory, and it fatigue cracked from there. The tube was cracked about 2/3 of the way around. I didn't see it until I took my firewall off during the restoration. You never know!

51fixer, Matt Gunsch and Stoney have more experience than I do, so hopefully they'll chime in as well.

Matt Gunsch · **Posted:** Mon May 07, 2012 11:47 pm

if it hasn't been done, replace all the mounting hardware for the Vertical and Horizontals and recheck the torque everytime the tail panels come off, I would also look at the vertical fin VERY closely. I had one that looked perfect, but you could poke your finger thru the ribs. If you have no idea when they were replaced, I would think about replacing the 8 bolts that hold the fuselage to the wing.
Doing acro in the 6 is not that hard on the airframe, since they operating at lower weights than they did in WWII, but doing a snap roll in a 6 scares the willies out of me, that is a lot of twisting on a airframe.

Ken · **Posted:** Fri May 11, 2012 5:43 pm

Good points guys, thanks for sharing. I'll pass this info on - and still looking for more.

Randy Haskin · **Posted:** Sat May 12, 2012 8:05 am

bdk wrote:

Other than the attach angle AD which stems from a metal fatigue issue

Isn't the attach angle issue a product of corrosion?

51fixer · **Posted:** Sat May 12, 2012 8:40 am

Randy Haskin wrote:

bdk wrote:

Other than the attach angle AD which stems from a metal fatigue issue

Isn't the attach angle issue a product of corrosion?

The issue lead to an inflight separation of a wing at low altitude in FL several years back.
A crack in the center wing stress door angle progressed from counterbore edge for a screw to counterbore edge until it grew.
This was a L/H wing which can be exposed to high loads in the case of the wing tip striking the ground in a ground loop.

51fixer · **Posted:** Sat May 12, 2012 8:51 am

AD for the Attach Angle-
http://rgl.faa.gov/Regulatory_and_Guida ... ction_.pdf

From the AD text-
SUMMARY: The FAA is adopting a new airworthiness directive (AD) for Rockwell International
(Aircraft Specification No. A-2-575 previously held by North American and recently purchased by
Boeing) Models AT-6 (SNJ-2), AT-6A (SNJ-3), AT-6B, AT-6C (SNJ-4), AT-6D (SNJ-5), AT-6F
(SNJ-6), BC-1A, SNJ-7, and T-6G airplanes; and Autair Ltd. (Aircraft Specification No. AR-11
previously held by Noorduyn Aviation Ltd.) Model Harvard (Army AT-16) airplanes. This AD
contains the same information as emergency AD 2005-12-51 and publishes the action in the Federal
Register. It requires immediate and repetitive inspections of the inboard and outboard, upper and
lower wing attach angles (except for the nose angles) of both wings for fatigue cracks; and, if any
crack is found, replacement of the cracked angle with a new angle. This AD is the result of a report of
a Rockwell International Model SNJ-6 (AT-6F) airplane crash that occurred on May 9, 2005,
resulting in two fatalities. We are issuing this AD to detect and correct any fatigue crack in the
inboard and outboard, upper and lower wing attach angles (except for the nose angles) of either wing,
which could result in failure of the wing. This failure could lead to loss of control of the aircraft.

51fixer · **Posted:** Sat May 12, 2012 9:07 am

Stoney here on WIX has been a big part of the NATA which all T-6 type owners and pilots should join. http://www.northamericantrainer.org/index2.htm
They have an AMOC (Alternate Means of Compliance) for the Attach Angle AD insp.
Details here-
http://www.northamericantrainer.org/amoc.htm

51fixer · **Posted:** Thu Aug 30, 2012 10:28 am

This was sent to me by local FSDO and is what they use to satisfy whatever FAA order they are following-

N Number: Serial Number: _______________
Model: ___________
Date accomplished: __
Location: ________________
Certification Category: ___________
Last Annual Inspection: ___________________________
Engines Times: #1_________ Hrs, SMOH _________Hrs
Propellers: #1_________,
Last 91.411: Altimeter System inspection/test completed on: _Yes / No__
Date:___________
Last 91.413: ACT Transponder inspection/test completed on: ___________
Last 91.207 ELT inspection completed on: _Yes / No__Date:____________
ELT Battery next due at: Yes / No__Date:_ ________
Airframe TT: _________hours
Hobbs Meter Reading: ________ hours
Last Wt & Bal completed on: ________
Aircraft Registration issued on: __________ Next due at: ____________
Airworthiness Certificate issued on: ___________
Aircrew Parachutes: ________________
Flight Manual: _Yes / No__Date:___________________
Annual Airshow Letter: _Yes / No___________
Seat Belts (TSO Tags): __Yes / No___________

Stoney · **Posted:** Thu Aug 30, 2012 11:19 pm

I agree with everything stated above, anything as old as the T-6/SNJ/Harvard should be treated with respect after all the first flight will be 75 years ago next year.
Remember when your out of T-6s, you're out of fighter trainers.
NATA will have several get-together for the first flight next year, check our web site later this year.

bdk · **Joined:** Sun May 02, 2004 1:16 am **Posts:** 11281

Randy Haskin wrote:

bdk wrote:

Other than the attach angle AD which stems from a metal fatigue issue

Isn't the attach angle issue a product of corrosion?

My understanding is that the fatigue crack issue led to an inspection AD which uncovered a number of aircraft with previously undected (although they probably should have been detected) intergranular corrosion issues.

The fatigue cracking issue emanates from the attach bolt holes. That's why the bolts need to be removed to perform the inspection.

51fixer · **Posted:** Wed Sep 05, 2012 2:19 pm

bdk wrote:

Randy Haskin wrote:

bdk wrote:

Other than the attach angle AD which stems from a metal fatigue issue

Isn't the attach angle issue a product of corrosion?

My understanding is that the fatigue crack issue led to an inspection AD which uncovered a number of aircraft with previously undected (although they probably should have been detected) intergranular corrosion issues.

The fatigue cracking issue emanates from the attach bolt holes. That's why the bolts need to be removed to perform the inspection.

The crack issue seemed to come from the edge of the counterbores done to have a flat spot for the screw heads to sit on that connect the attach angle to the skin and structure of the stress door or wing. If the counterbore tool has a sharp point rather than a radius on the OD of its cutting edge it leaves a sharp transition at the edge of the bore it cuts. The edge closest to the flange of the counterbore cracked and connected to the next one and so on. This was along the fwd side of the angle on the removable stress door on the L/H side of the center section.
This was per a conversation with the FAA Engineer who was listed on the original AD several years ago.
The Stress Door Angle attach design was different on the T-6F designed in 1945. The counterbores were smaller as they used HiLoc Pins and Collars rather than NAS screws and nuts. IIRC I also believe they increased the dia of some of the rivets.
Attach angles do corrode but the AD was in regards to the crack that caused the wing to fail.
The L/H wing does also get wacked on the ground during groundloops far more than the R/H wingtip. That can also increase the load induced and over time could be a factor in this type of a failure.

The Inspector · **Posted:** Wed Sep 05, 2012 3:17 pm

You are more likely to find IGC in things made of 7075 T6 which was a very popular aircraft material in SOCAL, doing 'C' and 'D' checks on an MD-80 would reveal metal that looked like a wet dark gray phone book and 2024 T3 on a 727 or 737 would be more fretting or surface type.

51fixer · **Posted:** Wed Sep 05, 2012 3:54 pm

The Inspector wrote:

You are more likely to find IGC in things made of 7075 T6 which was a very popular aircraft material in SOCAL, doing 'C' and 'D' checks on an MD-80 would reveal metal that looked like a wet dark gray phone book and 2024 T3 on a 727 or 737 would be more fretting or surface type.

I've send a lot of exfoliating on 2024 extrusion as well as pitting, tracks, bubbles.
Some WWII parts and skin used 2014.
Some skin was made from bare and anodized, particularly on Grumman and early war/prewar NAA. Since the surface is already grey you look for bubbles or bumps. Getting the surface wet helps by using the reflections.
Some of the heat treating during the WWII time period leads to corrosion as they were doing such large batches. The time between leaving the oven or heat source and quenching is important. If you get outside a window of time it can effect the materials corrosion resistance. I've seen whole ribs in a flight control not be there, just rivets in the holes and a few very small crusty pieces but every other part was in perfect condition.

Ken · **Posted:** Fri May 03, 2013 6:03 pm

Matt Gunsch wrote:

but doing a snap roll in a 6 scares the willies out of me, that is a lot of twisting on a airframe.

The Aeroshell guys do the 2-ship Avalanche (loop with inverted snap at the top) at each show. They may only be seeing 85-90 MPH at the top, though. IIRC, they have used the same T-6s for years - wonder if they've seen any adverse effects?

Ken

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