Attention T-6 Operators

[stumac]

The counterweight bolt you are refering to is technically called a counterweight bearing shaft and I agree with you that it could be a problem because I have had one of these break on one of the T-6's that I have maintained. The symptoms we had after it failed was a moderate vibration, a prop that was very sluggish to cycle back and forth on the ground and you could see the hub cylinder wobbling (not running true).
Did you have fun trying to get the broken threaded part of the bolt out of the cylinder?
I wonder how much of this stuff actually gets reported to the FAA?
They can't fix it if they don't know about it.
I think that this problem could be avoided by greasing the prop properly and more often. I used deal a lot with Bernie from Virginia Propeller (he died a few years ago) and he always preached to me that if it isn't slinging grease then there isn't enough. The pilots hated it.

[Chuck Gardner]

I had a long conversation with Fred from the FAA about the failure and was told that corrosion had nothing to do with the failure, and that it was a stress crack that took along time to devolop. The FAA seems to want a AD, even though it is not needed IMO. I am sorry it happened, but 2 failures is 65+ yrs is not a trend. He kept citing the South African inspection program and that they never had another failure, but he could not tell me how many they found to be cracked and the hrs in service of each found to be cracked. I believe the FAA is over reacting and the attach angles can be inspected as they all ready are, during a annual inspection. When I do a inspection, I look for corrosion, but I also go over the angles with a 10X glass. I have worked on a dozen or more various T-6 versions and have never found a attach angle cracked, I have found corrosion, which has caused me to replaced the angle.

Any added inspection on the attach angles, other than a visual inspection with a 10x or stronger glass is not needed, and will in the long run, cause more damage than it will detect. I have seen too many owners and A&P mechanics that did not know how to strip paint from aluminum correctly, I have seen them using steel wool, steel brushes, sanders, wiping paint stripper away and not netrulizing it with water. A large number of owners, if they have to strip the paint from the angles are going to leave them bare to make the next inspection easier, and that will open them for even more corrosion damage.

There is a more critical failure point in the T-6 which the FAA does not care about because no one has died, YET. The counter wieght bolt on the Ham standard prop has failed on 3 different planes I have worked on, and there was nothing in common, all had different times, were overhauled by different shops. 2 failed on T/O which almost caused the loss of the plane and crew, and 1 was caught before it failed.

Wow, this is a very intelligent post! Thanks Matt, well said.
Remeber that the aero-news article stated that the FAA was asking for imput towards a fix for this problem by the end of this week. Contacting them with good suggestions will help us all. We are all in this together.

[HarvardIV]

Remeber that the aero-news article stated that the FAA was asking for imput towards a fix for this problem by the end of this week. Contacting them with good suggestions will help us all.

Who is the contact in the FAA, and who will step up to the plate to contact them. I can forward the applicable portions of this discussion to them in MS Word.

[Rob Mears]

Does anyone have a photo showing the wing attach angles? I'd be interested to see a detailed shot of the area in question.

[bdk]

An important posting from the EAA:

http://www.warbirds-eaa.org/news/12005%20-%2005_31%20-%20FAA%20Seeks%20Important%20Information%20from%20T-6%20Owners_Operators.html

Here is the South African procedure (including instructions on jacking and removing wing bolts):

http://www.warbirds-eaa.org/southafrican_sb.pdf

The FAA's Airworthiness Concern Sheet:

http://www.warbirds-eaa.org/T6_airworthiness_sheet.pdf

[bdk]

Does anyone have a photo showing the wing attach angles? I'd be interested to see a detailed shot of the area in question.

This isn't very good, but on short notice...

http://www.at6parts.com/page10.html

[Brad]

This is an email that I recieved as a courtesy copy from a long time T-6 owner and airshow pilot. It was sent to other people with the FAA/EAA that are interested in this subject.

"I'd like to bring to your attention that most of these warbird wing failures are the result of over G's, in mock air combat. Air combat, unlike normal aerobatics, uses lots of barrel roll type maneuvers to gain advantage of reversing position.
Rolling G limits in fighter aircraft is generally 2/3 of the normal maximum G limits. The stress of the climbing wing could be exceeding the limits on that wing while the G meter is indicating within the limits.
Air combat operations that don't address this issue give the whole community a bad rap. Novice air combat competitors can whip on an over G before the instructor can stop them.
The only way to really know what the rolling G loads that have occurred are to have recording G meters in the wing tips. If they could be electrically presented to the cockpit, that would be better, but some type of devise for this event should be incorporated with air combat operations."

I don't know if the Florida accident had anything to do with pretend combat flights or not, but in light of the T-34's recent trouble and that potential in other planes, the g meter idea might not be bad.

[HarvardIV]

Good points guys:

I sent the EAA regulatory rep a letter about this issue, and quoted the most relevant comments forom this discussion. Here was the EAA/FAA response:

I apologize for this canned response but I need to take advantage of this method of communication to keep up with the many calls and emails I have received on this issue. First, thank you for taking the time to respond to the notice and for providing your thought; it is appreciated. EAA and Warbirds of America (WOA) have been actively working this issue, with the primary help of Rick Seigfried WOA Board member and a NTSB designated "party to an investigation" of the recent T-6 accident. In addition, we have been in constant contact with the various FAA offices that are working this issue.

Currently, after review of the information that we have, EAA and EAA WOA concur with the need to inspect the entire fleet for cracks in the lower wing attach angles and, therefore, agree that there is a need for an airworthiness directive to be issued against the subject aircraft.

EAA and WOA are still reviewing the considerable input we are receiving from owners and maintenance professionals regarding the issue outlined in the ACS dated May 25, 2005. So far we have the following proposed suggestions for the FAA:

· The initial AD should NOT be repetitive.

o All owners/operators should be required to perform a dye penetrant inspection.

o Upon completion of the inspection the results, serial number, model number, total time of the airframe and the average hours flown for the last 5 years should be reported back to the FAA.

· A modified version of the South African inspection should be used, not the identical version.

o Under development by Rick Seigfried and others.

· Florescent dye penetrant should not be required but should be allowed as an alternate to non-florescent.

· Alodine should be listed as an appropriate alternative to paint for corrosion protection following the dye penetrant inspection.

· The AD should allow for the flight of the aircraft in the normal category for up to 10 hours to allow for movement of the aircraft to the home base and/or maintenance facility without the need for a ferry permit.

· The AD should not require the inspection if previously conducted within the preceding 12 calendar months and if less than 200 hours have been accumulated since the last inspection.

· The AD should call for annual removal of the wing joint bolting angle cover and the visual inspection for cracks and corrosion of the wing joint bolting angle.

EAA and WOA are particularly concerned that the agency may require repetitive inspections without sufficient data to support the establishment of the required inspection intervals. EAA and WOA are asking the FAA to wait until the initial inspection of the fleet has occurred and the data, along with service life of the fleet, can be accumulated and evaluated by the agency and the industry. Once that information has been evaluated a determination as to the duration of a repetitive inspection can be appropriately determined.

In addition EAA and WOA are concerned with the larger issue of mock air-combat and aerobatic training activities in aircraft. We have a concern that this particular failure, and other similar ones, are a result of aircraft seeing higher and more repetitive stresses than they were designed for. We assert that the real issue is the need to address these high stress operations of aircraft as opposed to implementing new inspection procedures on an entire fleet of aircraft. We acknowledged that we must address the current issue at hand but stress that we are willing and able to address what we believe is the real and long- term solution; the establishment for standards for the use of aircraft in mock air-combat and or other high stress aerobatic operations.

Please continue to send in your comments and let us know your thoughts about our initial position on this issue. Copies of the Airworthiness Concern sheet and the South African procedure are linked to the stories on both EAA and WOA web sites; reference www.eaa.org and http://www.warbirds-eaa.org/.



EXPERIMENTAL AIRCRAFT ASSOCIATION (E.A.A.)

Earl Lawrence

Vice President Industry and Regulatory Affairs

I don't totally agree with it, but I think the technical people in the EAA know a lot than me

[srpatterson]

I totally agree with it...

[jcw]

HarvardIV

Earl Lawrence wrote

"The AD should call for annual removal of the wing joint bolting angle cover and the visual inspection for cracks and corrosion of the wing joint bolting angle".

I agree with the one time inspection within 10 hours, however I do not agree with the repeditive inspection as it is already covered under AD 50-38-01 for all AT6 acft and should be accomplished during the annual anyway. If you can pass this on to Earl Lawrence they might want to review the existing AD's on the acft. There are only 6 current AD's for the acft (AT6C / SNJ4)

I'm waiting for the AD release and then will apply for and alternate method to use eddy current inspection so i don't have to strip the paint.

[Stoney]

I want to let everyone know that NATA is a party to the investigation and Rick is working with us. We have a team of five people on this.


[Aircraft Mech Paul]

Hi All,

This is my first post in a while, been on vacation. But, if I may offer some info on these wing atach angles. I have been involved in the restoration of a G model for quite some time. We are close to begining the process of mating the wings again. But the only thing that is holding us back on this is the relative cost of the new wing attach angles, both to the wing center section as well as the outboard wing poanles themselves. as the originals are badly corroded with (IG) intergranular corrosion or if you prefer the other accepted term, exfoliation corrosion. I also did so work with PoF East, when the were located in the Minneapolis area and accoriding to their (then) chief mechanic, on T-6 wing attach angles, ANY corrorsion with the exception of very light corrosion that can be removed with gentle rework is PROHIBITED. There is NO rework allowed for thse particular parts do their structural signifigance. And from what I recall these parts are availible from Lance Air, but each section has a starting price of close to $200.00. And on the project I am involved with the, we have a considerable amount of them to replace. This is not an easy job to accomplish unless you have some fair amount of aircraft structural background.

Additionally, performing a flourescent penatrant inspection of these attach angles would best be served by someone who knows and is experianced in this method of inspection. Additionally, intergranular or exfoliation corrosion is hard to inspect for because flourescent penatrant inspection is a SURFACE inspection only. And in that I mean if the top surface "looks" okay, it may have defects beneath the surface the FPI (flourescent pen inspection) will NOT find.

As a side note, and I am not attempting to solicit myself in anyway here, but I make my living now, in performing NDT inspection on aircraft. I am also a fully liscened A&P as well as I am qualified in 5 other methods of NDT as well as FPI, and have a considerable amount of structures experiance, from Warbirds to Jetliners. If I can be of any help...shoot me a note.

One last item, as this is an AD note in the making it seems, when the final dispostion comes through from the FAA. It is MANDATORY to follow the AD Note..AS WRITTEN to the LETTER be be in compliance. No deviations, except those in the proposed AD would be allowed.

Just my two cents...but again...if you need any help...please...feel free to shoot me a note.

Paul

[HarvardIV]

JCW:

Although I don't know near as much as you high time veteran pilots, I agree with you. To me it would be ideal if the EAA would ask the FAA to "strongly recommend" the inspections, and not turn it into an AD. Since, like you said, it's already covered in another AD. I'll pass it on, someone's got to step up to the plate.

[Matt Gunsch]

I guess no one can read. In my conversation with Fred from the FAA, he stated that corrosion did not cause the failure, it was a stress crack, so it is not covered by the 50-38-01( see below). Those who contact the FAA and say it is all ready covered by the AD are wrong and will make it worse. The AD can be admended to include a 10x inspection of the attach angles

My recomendation is a inspection with a 10x glass at every inspection. No need to paint strip the angles if the paint is thin enough.

50-38-01 NORTH AMERICAN: Applies to All Model AT-6
Series Aircraft.
To be accomplished at the next annual inspection and at
each succeeding annual inspection thereafter.
Several recent incidents have indicated that the
inspections presently required are not sufficiently
comprehensive to reveal all areas of the airplane which may
have been adversely affected by intergranular corrosion, and
that the required inspections should be repeated periodically.
Accordingly, in order to minimize the possibility of
structural failure due to such corrosion, the following must be
accomplished:
Inspect all accessible structural aluminum alloy
components for evidence of intergranular corrosion particularly
in the following locations: At the upper and lower deck and
the most forward and two aft bulkheads in the monocoque
fuselage; frame around the baggage door; inboard end of
horizontal stabilizer spars; fuel cell doors in the wing center
section; wing attach angles; two inboard ribs on each outer wing;
trailing edge ribs above flaps; and the outboard rib of the
wings, especially at the trailing edge. Full use should be
made of all access provisions to accomplish as thorough an
inspection as possible.
In conducting these inspections, full reliance cannot be
placed on visual examination alone. A screwdriver or other
instrument should be used to explore for dull sounding areas and
for material which may be penetrated easily by pressure applied
to the screwdriver tip or similar sharp point. Areas adjacent
to joints and sheared edges should be examined thoroughly.
Formed material in particular has been found to be
subject to rapid intergranular corrosion, because of poor
heat treatment of parts, which were formed in the annealed
condition, and later heat treated.
All corroded parts must be replaced.
This supersedes AD 47-41-01.

[jcw]

Matt

As an IA when i do a visual inspection of the wing attach fittings as per 50-38-01 every annual i am not looking for just an indication of corrosion but for anything that will render the part non airworthy and that includes cracks. as i said in the earlier post the PROPOSED AD was going to add an annual visual inspection

Earl Lawrence wrote

"The AD should call for annual removal of the wing joint bolting angle cover and the visual inspection for cracks and corrosion of the wing joint bolting angle".

if you want to get specific on how you inspect it then add that wording to the AD. as for cracks, visual or die penetrant doesn't catch them all, and if that is the intent then you need something else, ie eddy current. I personnally am going to do an eddy current check on mine and when the AD comes out will file for an "alternate inspection method" to make it legal...

take care