AD 2005-12-51

[zedzil]

I am new to the forum so some of the questions might have been discussed before.

After many years of being away from this type of airplane (though not from aircraft structural engineering - I was a DER in the past), I am involved in an annual inspection of an SNJ-5 and of course was asked to look into this AD.

After studying it I feel that it is a very onerous and unreasonable one.

Questions:

1. I couldn't find anywhere an analysis that will support the requirement to repeat the inspection every 200 hours. Why 200? Does anyone have the statistical data showing how many T-6s/SNJ lost their wings because of attach angle failure since 1937? Since 1967? Since 2007?

2. Has anybody done a crack propagation study/test on the angles?

3. Has there been any remedial action generated that will eliminate the requirement for repeat inspections? A rework of the angles, fasteners, etc.?

4. Do you people think that a fix that will eliminate the requirements of the AD is worthwhile to look into?

5. Has anybody found the AMOC offered by NATA a worthwhile investment?

6. Have you operators found the burden of the AD so small that it is not worthwhile to address the issues listed in the questions above?

Any feedback will be welcomed.

Jake

[CraigQ]

I am new to the forum so some of the questions might have been discussed before.

After many years of being away from this type of airplane (though not from aircraft structural engineering - I was a DER in the past), I am involved in an annual inspection of an SNJ-5 and of course was asked to look into this AD.

After studying it I feel that it is a very onerous and unreasonable one.

Questions:

1. I couldn't find anywhere an analysis that will support the requirement to repeat the inspection every 200 hours. Why 200? Does anyone have the statistical data showing how many T-6s/SNJ lost their wings because of attach angle failure since 1937? Since 1967? Since 2007?

2. Has anybody done a crack propagation study/test on the angles?

3. Has there been any remedial action generated that will eliminate the requirement for repeat inspections? A rework of the angles, fasteners, etc.?

4. Do you people think that a fix that will eliminate the requirements of the AD is worthwhile to look into?

5. Has anybody found the AMOC offered by NATA a worthwhile investment?

6. Have you operators found the burden of the AD so small that it is not worthwhile to address the issues listed in the questions above?

Any feedback will be welcomed.

Jake

As an A&P who has set up more than a few T-6/SNJ's for this inspection I can tell you the AMOC is well worth the investment. For the owner it is cheaper hands down. With the AMOC the labor costs pulling about 11-12 bolts on the lower attach angles for the 200 hr eddy current inspection is far and away faster and less labor intensive. Pulling all the bolts upper and lower every 200 hrs and doing fluorescent dye pen is not something I personally would/do not look forward to doing.

What is unreasonable about detecting a crack in a wing attach angle that could prove catastrophic? The incident that brought about the AD resulted in the loss of two lives.

As for the rest of your questions give Fed Guerin of the Los Angeles Flight Cert office and have a talk with him. His contact info is in the AD.

[zedzil]

CraigQ

As someone who has set up more than a few T-6/SNJs for this inspection, do you recall how many cracks were discovered by these inspections?

Jake

[CraigQ]

CraigQ

As someone who has set up more than a few T-6/SNJs for this inspection, do you recall how many cracks were discovered by these inspections?

Jake

None to date I have been involved with. By others I cannot say.

Again, it's the FAA you have to convince. The FAA says do it, it gets done, it's not an option. You don't like it or agree with it then you have to convince them it's unnecessary. You mentioned having been a DER, you should know the road to take.

[shrike]

CraigQ

As someone who has set up more than a few T-6/SNJs for this inspection, do you recall how many cracks were discovered by these inspections?

Jake

None to date I have been involved with. By others I cannot say.

Again, it's the FAA you have to convince. The FAA says do it, it gets done, it's not an option. You don't like it or agree with it then you have to convince them it's unnecessary. You mentioned having been a DER, you should know the road to take.

Has the FAA ever withdrawn a non-emergency AD? It doesn't cost them anything to keep it in place, and by allowing as it may not have been truly necessary, they fear opening themselves to legal action.

[CraigQ]

CraigQ

As someone who has set up more than a few T-6/SNJs for this inspection, do you recall how many cracks were discovered by these inspections?

Jake

BTW, as an aside to this, while we have not found any cracked attach angles. We have found corrosion during the process that required replacing a lower attach angle.

[bdk]

Yes, more intergranular corrosion discovered than cracks. This AD is forcing people to look at stuff that should have been obvious with a good visual inspection.

[Stoney]

The North American Trainer Association sells the AMOC for $350, contact # is 360-256-0066.

[bdk]

Just my free opinion here... You get what you pay for!

Questions:

1. I couldn't find anywhere an analysis that will support the requirement to repeat the inspection every 200 hours. Why 200? Does anyone have the statistical data showing how many T-6s/SNJ lost their wings because of attach angle failure since 1937? Since 1967? Since 2007?

What good does this data do you? Compliance with an AD note is mandatory. One lost wing is too many!

2. Has anybody done a crack propagation study/test on the angles?

This is likely done by fatigue analysis of the part configuration and the alloy used for the attach angles.

3. Has there been any remedial action generated that will eliminate the requirement for repeat inspections? A rework of the angles, fasteners, etc.?

No. An initial flaw size has to be assumed and crack growth follows that. The NATA AMOC NDI method allows a smaller flaw size to be detected so you can go longer between inspections.

4. Do you people think that a fix that will eliminate the requirements of the AD is worthwhile to look into?

Only if you are willing to get an STC for either thicker attach angles (lower stress, but may not fit the available space) or ones made from a more fatigue resistant material. If you are starting a business that depends on how many you think you can sell, if you are just fixing one aircraft it wouldn't make sense.

5. Has anybody found the AMOC offered by NATA a worthwhile investment?

Probably depends how much you fly. You have to do a cost to benefit analysis based upon usage.

6. Have you operators found the burden of the AD so small that it is not worthwhile to address the issues listed in the questions above?

My wings are removed for restoration so the dye check was easy for me. No bolts needed removal. I got the dye check kit from Aircraft Spruce. That is my one data point. The fastener removal requirement does not seem particularly onerous. You should contact a shop in your area that has done this work to find out how many hours it took and what the cost was.

[Matt Gunsch]

IMO, the AD is more a butt cover than to correct a problem. While there has been attach angles found with corrosion, that is all ready covered by AD 50-38-01, which covers the entire airframe looking for corrosion. I have seen T-6s after accidents with the entire wing pulled off, with the attach angles intact with all the attaching rivets sheared off, but still bolted to the center section. It was a bull excrement AD then, as it is now.
Here is 50-38-01, How can anyone doing a annual inspection on a 6, say they complied with the AD, but then find corroded attach angles during that AD inspection ?

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.

[DELEQ]

Hi Matt,
In my opinion the Problem is that, as you quoted correctly, AD 50-38-01 Applies to All Model AT-6 Series Aircraft, but not the T-6G Model, while the Wing Angle AD does. I was at first also unsure whether AD 50-38-01 is also valid for the “G” Model, but if you pull up the ADs on the FAA website sorted by models, it shows up for all the AT-6 Aircrafts but not for the T-6G.
I have heard that this comes from the fact that all the T-6G were remanufactured from all the different AT-6 models around 1949/1950. At this time they used better corrosion protection, at least that’s what I heard.
So I think AD 50-38-01 is no substitute for the Wing Angle AD, for two reasons:
-It deals with corrosion and detecting it, while the Wing Angle AD deals with Fatigue cracking
-It is only applicable to the AT-6 Aircrafts, while the Wing Angle AD applies to all AT-6 / T-6 models, including the T-6G.

Stefan

[Matt Gunsch]

Hi Matt,
In my opinion the Problem is that, as you quoted correctly, AD 50-38-01 Applies to All Model AT-6 Series Aircraft, but not the T-6G Model, while the Wing Angle AD does. I was at first also unsure whether AD 50-38-01 is also valid for the “G” Model, but if you pull up the ADs on the FAA website sorted by models, it shows up for all the AT-6 Aircrafts but not for the T-6G.
I have heard that this comes from the fact that all the T-6G were remanufactured from all the different AT-6 models around 1949/1950. At this time they used better corrosion protection, at least that’s what I heard.
So I think AD 50-38-01 is no substitute for the Wing Angle AD, for two reasons:
-It deals with corrosion and detecting it, while the Wing Angle AD deals with Fatigue cracking
-It is only applicable to the AT-6 Aircrafts, while the Wing Angle AD applies to all AT-6 / T-6 models, including the T-6G.

Stefan

Stefan, the AD reads ALL AT-6 Series, is the T-6G not part of the series ? The AD does not say SNJ, so are they exempt ? but the SNJ is part of the series as is the T-6G. When the T-6G was remanufactured, they did not replace skins or parts other than those needed to bring the airframe up to a set standard.

The better corrosion protection on the G models does nothing to prevent corrosion caused by in-correct heat treating of the aluminum, that can only be done by replacement of parts.

Last edited by Matt Gunsch on Tue Jun 21, 2016 12:50 pm, edited 1 time in total.

[bdk]

AD 50-38-01 Applies to All Model AT-6 Series Aircraft, but not the T-6G Model, while the Wing Angle AD does. I was at first also unsure whether AD 50-38-01 is also valid for the “G” Model, but if you pull up the ADs on the FAA website sorted by models, it shows up for all the AT-6 Aircrafts but not for the T-6G.

T-6G was in military, not civilian service at the time, so the AD didn't apply. Common sense would seem to indicate it probably applies now.

You could say that the T-6G was made from the AT-6 series aircraft, so those AD notes would still apply. Also, during maintenance aircraft may be "de-modified" using older replacement parts. You could install a replacement wing or tailcone for instance.

The TCDS treats all US built models the same.

[bdk]

I understand the pedantic nature of this thread, but it seems like a lot of effort is being expended to come up with reasons not to inspect something actually quite simple to do. Isn't a corrosion inspection part of every annual? How could you call yourself an IA and not notice intergranular corrosion on a tailcone longeron or around the baggage door?

[Matt Gunsch]

Stefan,
When I go to the FAA web site and pull up ADs, I search for North American Aviation, but there are no ADs, but if I look up boeing, I get ADs for the T-6, so going by your process, there are no ADs against the North American Aviation manufactured T-6 series, but there are ADs against the boeing built T-6s.