But some of them have more onerous AD's and I forget what the AD number is now. The later 500U and S series (Utility category), the 681, 685 and the 690, A and B series. Those are the ones that suffer from dissimilar corrosion form the strap. Basically anything made in the late 60's to mid to late 70's are susceptive. Before that they didn't have the stainless steel strap, and after that they removed it. To eliminate the inspections you need to do the STC, which is a big item. That's $100K fix. Otherwise it's a 36 month recurring inspection where fuel bladders need removing, so it costs around $15K per inspection, or $5K per year in reserves. It's not unsubstantial.