All, Mike Sigman, the previous owner, and I spoke last night while I was on my way to DFW. He said he had looked at two Ercoupes, an original 415C with no mods and a 415 with bucket seats. The original airplane had two holes on centerline in the shallow 'V" of the main spar cap that the tab on the seat pan fastens to. Most other people I've talked to have these two holes. I believe this is the factory configuration. According to Mike, the 'coupe with bucket seats had exactly the same pattern as my main spar cap-- four holes on the left outboard, two holes on the left inboard, two holes in the center of the "V", two holes in the right inboard, and four holes in the right outboard. Our new theory is that my airplane once had bucket seats. There is no record of this and no 337 or STC in the FAA file, so it was probably just a logbook entry. We think another owner probably removed the buckets and went back to the original seat. The A&P then probably drilled 12 holes in the front lip of the seat pan and installed 10-32 screws rather than leaving the holes open in the main spar cap so the pan fit would flush with the top of the spar cap. Since re-installing the original seat would not require a 337, we are looking to see if there is a logbook entry to confirm this.
Here's the interesting thing-- there are probably a LOT of Ercoupes that had bucket seats installed and had a 337 submitted. By definition, that would mean these are FAA-approved modifications that would have additional holes drilled into the main spar cap to mount the seats. I urge 415 owner with extra holes in the main spar cap to look for documentation and 337's to show that they may have had an FAA-approved bucket seat installation. That doesn't necessarily mean that the additional holes could not be a structural integrity issue, but it would at least prove that the FAA did not think they would create a problem at the time of approval. Mike is going to try to get pictures of the Ercoupe with bucket seats to corroborate this. Unfortunately, without documentation my holes are probably unauthorized. Regards, Dave
