Questions from a Potential 337 Buyer

wmarion6 · #1 02-25-11, 07:14 PM

I've been thinking about buying a P337 but have been concerned about some of the posts on various forums about the AD's related to wing problems. Is this a closed issue or do I need to worry about compliance and on-going inspections?

Thanks

hharney · #2 02-26-11, 08:36 PM

There are some potential SID's (Supplemental Inspection Documents) that have been proposed by Cessna. This is an ongoing effort pushed by the FAA based on "Aging Aircraft", something all manufacturers will be facing. There is more information on the situation here

http://www.337skymaster.com/messages...ead.php?t=2513

If you study this thread it will help to define the process. For more information and if you really want to learn about Skymasters, join us in Dayton, OH on June 1 for the Anniversary Fly-in event.

The AD that is most current to this aircraft only pertains to those modified with Aviation Enterprises wing extension fuel tanks and winglets. If you don't own a Skymaster yet just beware of any modifications to the wings. Ask questions, talk to a Skymaster experienced owner or mechanic about these before proceeding.

http://www.337skymaster.com/messages...ead.php?t=2771

There is one other AD to have the spar inspected at 5,000 hours but this AD has been published for many years.

Hope this helps

Ernie Martin · #3 02-27-11, 08:27 PM

One point you will find about the SIDs in the reference provided by Herb is that, absent extraordinary circumstances, they will not apply to aircraft on Part 91 operations.

This is clearly spelled out in the FAA order that led to the SIDs and further supported by what has happened to other Cessna twins subject to SIDs (where none of the SIDs apply to Part 91 except one that became an AD after cracks were found in numerous aircraft and there was an in-flight loss of a wing).

Ernie

Denhamblin · #4 02-28-11, 03:13 PM

Quote:

Originally Posted by hharney

There are some potential SID's (Supplemental Inspection Documents) that have been proposed by Cessna. This is an ongoing effort pushed by the FAA based on "Aging Aircraft", something all manufacturers will be facing. There is more information on the situation here

http://www.337skymaster.com/messages...ead.php?t=2513

If you study this thread it will help to define the process. For more information and if you really want to learn about Skymasters, join us in Dayton, OH on June 1 for the Anniversary Fly-in event.

The AD that is most current to this aircraft only pertains to those modified with Aviation Enterprises wing extension fuel tanks and winglets. If you don't own a Skymaster yet just beware of any modifications to the wings. Ask questions, talk to a Skymaster experienced owner or mechanic about these before proceeding.

http://www.337skymaster.com/messages...ead.php?t=2771

There is one other AD to have the spar inspected at 5,000 hours but this AD has been published for many years.

Hope this helps

I just wanted to add that another AD is due out soon that will include 337s modified with Flint Aero tip tanks. This AD will not effect 337 with the 150 gallon main tanks which were offered, I believe, beginning in 1974 and stock in any subsequent year.

Justadude · #5 12-07-14, 12:00 AM

In my search for a 337, today I looked at a 1975 P337 that was in very good shape, good times on airframe and engines, and well equipped. The plane had the engines reman'd and all upgrades done in 204 by the Rocket Aircraft LLC. To my understanding, many were part of Riley back in the day.

The big question for all of the knowledgeable folks on the board is what to do with the AE wing tanks (plus fuel xfer/fuel dump equipment) that Rocket installed in 2004. I've read all of the treads on this board, plus anywhere I could find information. A lot of emotions to say the least. Is it best to walk away from this plane, insist that the seller go through the removal and final AD inspection, or negotiate in a $ value to accommodate the removal (and what would/could that $ amount be?). As an aside, I saw no skin cracks or smoking rivets when inspecting the top of the wings.

Appreciate the help here. I really like what these planes can represent in usefulness, while appreciating the complexity and financial commitment required.

Thanks in advance,
Bob

Denhamblin · #6 12-07-14, 11:37 AM

Quote:

Originally Posted by Justadude

In my search for a 337, today I looked at a 1975 P337 that was in very good shape, good times on airframe and engines, and well equipped. The plane had the engines reman'd and all upgrades done in 204 by the Rocket Aircraft LLC. To my understanding, many were part of Riley back in the day.

The big question for all of the knowledgeable folks on the board is what to do with the AE wing tanks (plus fuel xfer/fuel dump equipment) that Rocket installed in 2004. I've read all of the treads on this board, plus anywhere I could find information. A lot of emotions to say the least. Is it best to walk away from this plane, insist that the seller go through the removal and final AD inspection, or negotiate in a $ value to accommodate the removal (and what would/could that $ amount be?). As an aside, I saw no skin cracks or smoking rivets when inspecting the top of the wings.

Appreciate the help here. I really like what these planes can represent in usefulness, while appreciating the complexity and financial commitment required.

Thanks in advance,
Bob

Hello Bob,

The 1975 models should have the factory long range tanks (150.6 total capacity) as standard equipment (some call this the "long" wing). The wings in these aircraft are stronger than the earlier models. This is because they have "hat" type stringers that extend out to WS 170 (maybe it is 177, I don't recall exactly). At that point they splice into a "J" stringer. On the earlier models this transition occurs at WS 150. I do not know the details of the AD that affected those aircraft modified with the AE extensions but I can say that aircraft modified with Flint Tanks are not affected if they have the factory long range tanks.

One question I have is if the aircraft you are looking at had a gross weight increase over 4630 (4700 for turbo). I believe with some engine mods you could get the gross weight up over 5000 (I want to say 5240 for some reason). If it had a GWI and was operated above 4700 then I would have some concerns about the wings as my engineer didn't think that would be possible even with the "long" though he did not do calculations for a gross weight over 4700.

Another question would be whether the aircraft had winglets. Winglets can increase the load as well. We didn't look at that either since the Flints don't use winglets.

Again, you would want to follow the AD that affects the 337s modified with the AE STCs and, while I do think I have a copy of that at the office, I'm not sure of the details. I would expect that AE issued a SB to deal with that AD so you would need to follow that as well.

I can say that with the Flints you do not need to remove the tips. If you have the "short" wing you need a structural retrofit kit which beefs up the wing at WS 150 (a doubler at the rib at WS150 which spans about 3.5" inboard and 5" outboard, 3 stringer doublers that extend out from WS150 to WS177 and a forward spar doubler that does the same). These doublers are put on the exterior of the top wing surface and are provided for free for those aircraft modified before the issuance of the AD that affected the Flint modified aircraft. Labor costs are not included and you are looking at 30-35 hours to install the structural retrofit. If you have a "long" 337 with Flint tips there is no action necessary. Please note that with the Flint tips you have a limitation of keeping 12 gallons in each tip until your gross weight drops below 4330.

I hope this helps.

Denhamblin · #7 12-07-14, 11:45 AM

Quote:

Originally Posted by Justadude

In my search for a 337, today I looked at a 1975 P337 that was in very good shape, good times on airframe and engines, and well equipped. The plane had the engines reman'd and all upgrades done in 204 by the Rocket Aircraft LLC. To my understanding, many were part of Riley back in the day.

The big question for all of the knowledgeable folks on the board is what to do with the AE wing tanks (plus fuel xfer/fuel dump equipment) that Rocket installed in 2004. I've read all of the treads on this board, plus anywhere I could find information. A lot of emotions to say the least. Is it best to walk away from this plane, insist that the seller go through the removal and final AD inspection, or negotiate in a $ value to accommodate the removal (and what would/could that $ amount be?). As an aside, I saw no skin cracks or smoking rivets when inspecting the top of the wings.

Appreciate the help here. I really like what these planes can represent in usefulness, while appreciating the complexity and financial commitment required.

Thanks in advance,
Bob

One other thing. You can't just simply uninstall the Flint tips. You would need to replace the closeout rib in both wings since they are heavily modified when you add fuel tanks outboard of the closeout rib. I'm not sure what AE does with the closeout rib. Finding those ribs may be both difficult and expensive.

Justadude · #8 12-07-14, 11:46 PM

Thank you for the very quick and detailed response. Very much appreciated.

The 1975 model came with 150G. tanks as standard, and guess by default the "long" wing.

The Max Take Off Weight MTOW was increased from 4700 to 5120 through the AE Wing Exetension STC and AE Fuel Transfer STC. Max Landing Weight is unchanged at 4465. No change to standard 225hp turbo engines. The plane does not have winglets.

Regarding removal of the AE tips/tanks, I don't know how/if the close out ribs are modified. Also would assume that sourcing those may be a challenge, and then adding back on standard wing tips or Horton tips since it has the Horton Stol kit installed.

Understand the suggestion for caution for using the plane above 4700 lbs gross weight and potential concern. I have no way to measure how may of the 510 hours of flight time were above that level, since the AE tips were installed.

Once again, thank you for your comments.

Bob

JamesC · #9 12-08-14, 12:02 AM

For peace of mind you might have to search for over-stress micro-cracks in the spar from carrying the extra weight, with dye penetrant or acoustic emission techniques. All at a cost of course, along with removing the tanks.

Denhamblin · #10 12-08-14, 01:29 AM

Quote:

Originally Posted by Justadude

Thank you for the very quick and detailed response. Very much appreciated.

The 1975 model came with 150G. tanks as standard, and guess by default the "long" wing.

The Max Take Off Weight MTOW was increased from 4700 to 5120 through the AE Wing Exetension STC and AE Fuel Transfer STC. Max Landing Weight is unchanged at 4465. No change to standard 225hp turbo engines. The plane does not have winglets.

Regarding removal of the AE tips/tanks, I don't know how/if the close out ribs are modified. Also would assume that sourcing those may be a challenge, and then adding back on standard wing tips or Horton tips since it has the Horton Stol kit installed.

Understand the suggestion for caution for using the plane above 4700 lbs gross weight and potential concern. I have no way to measure how may of the 510 hours of flight time were above that level, since the AE tips were installed.

Once again, thank you for your comments.

Bob

Bob,

If the AE extension carried fuel then they likely needed to modify the closeout rib and replacement of those ribs would be necessary if you decided to remove the AE extensions. I don't even know if you can find new ribs for a 337 but with a 210 the cost of buying new (or reused) ribs is about $3,500 (last time I checked).

What is more important is whether you have to remove the AE extensions to comply with the AD (and if you need the additional fuel). If removal isn't necessary and you actually want the additional fuel then you may just want to do an inspection of the wing to ensure there are no issues with it.

I don't know what limitations may have been in effect to fly the aircraft at 5120. If there was a limitation to keep more fuel in the tips when flying at that weight then that would be a mitigating factor. Fuel out at the wing tips will counter the loads created by increasing the wing area. With my tips, you can not completely empty the tip tanks until your GW drops below 4330. With a GW at 5120 you would have to do the math to figure out if you could burn enough fuel in the mains to allow you to transfer the fuel from the aux tanks. But, again, I would look at the limitations of the STCs involved.