If you read the AD it says that if the aircraft is being flown low altitude high G flying such as pipeline surveying or military flying, the wing spar AD must be done at air frame total time of 3,000 hrs and repeated every 500 hrs thereafter. If the aircraft is not flown in high G flying then the AD must be done at 5,000 hrs total air frame time and repeated every 500 hrs thereafter. There are 2 parts to the AD inspection; Eddy Current inspection of 3 holes in the bottom of the front spar just outboard of the the strut, and a dye penetrant inspection of the rear spar web inside the inboard main fuel tank bay. The Cessna drawing that spells out everything we must do to covert an 0-2A or 0-2B from military to FAA Standard Registration, states that we must do the Wing Spar AD no mater what the total air frame time is. After this inspection then it must be repeated every 500 hrs. We have done more than 30 aircraft since specializing in Skymaster aircraft and have never seen a crack. It is true that the dye penetrant inspection part can be done by an A&P, however the Eddy Current parts has to be done by an FAA Repair Station Eddy Current qualified person. The costs for this Eddy Current qualified person varies around the country. I did an accident investigation of the 0-2A that broke apart in flight over central Florida a few years ago and there was no evidence of any cracks where the AD specifies the inspections.
Every thing I have said above about the Eddy Current part of the inspection applies only to the early model 337's and all 0-2's. Late model 337's wings were beefed up and the AD lists the applicable aircraft serial numbers. These late model 337's have rivets where the screws/bolts are in the early model 337's. Cessna's great wisdom in developing the SID inspections forgot to read the applicable aircraft serial numbers in the Wing Spar AD and made a SID inspections almost exactly the same wording as the Wing Spar AD but made it applicable to all Skymasters. The real problem is now in countries outside the US, the SID's are treated as mandatory. (This is another horror story).
The labor intensive part of doing the AD is taking the fuel tank covers off the top of the wings. If all the screw have not been off for a long time, many may have to be drilled out and some nut plates replaced. The problem is that one of the screws in the bottom of the front spar that must be removed to do the Eddy Current inspection, has a nut on the back side and the only access is in thru the fuel tank bay. I know the AD says there is an alternate method to do the dye penetrant inspection, but I cannot see how one could then see the rear spar web.
I bought one of the California Department of Forestry's 0-2A that had 11,000 to 12,000 total air frame time and they said it had a crack at the locations spelled out in the wing spar AD. It turned out that it did not have a crack at the AD locations but it had a crack where the wing tie ring is located.
If you want more information about our experiences give me a call;
Don Nieser, (02&337 parts guy) Commodore Aerospace Corp, 405-503-4686
nieser.02.337parts@juno.com