Own an aircraft for long enough and you’ll eventually be faced with a modification or repair that’s considered a major alteration. In FAA speak, that’s an official term and a big deal that almost always requires more than a logbook entry for returning the aircraft to service.
In a regulatory climate that’s been somewhat relaxing (especially in the avionics market) one of the most common and difficult questions to answer is whether a given repair or modification needs a special signoff. If you attempt to interpret the regulations, the requirements are more than paperwork. The two pertinent FARs involved are Appendix A to Part 43, which defines major repairs and alterations, and Appendix B to Part 43, which covers the recording of those major repairs and alterations.
Appendix A to Part 43 is extensive and covers major alterations to specific parts of the aircraft “when not listed in the aircraft’s specifications issued by the FAA.” Appendix A should be bookmarked because not only is it a starting point to determine if a given repair or mod is a major or minor alteration, it also covers owner-performed preventive maintenance. But for guidance on signing the work off, look to Appendix B because it deals specifically with the paperwork side.
For owner-performed major mods, it’s possible to bring the aircraft to a general aircraft repair shop (or even complete the work at the shop under its supervision) where an IA can inspect the work and sign off the required FAA Form 337. It’s not uncommon for IAs to sign off work done by A&P mechanics and even people who don’t have a certificate. But in doing so, the IA is certifying that the proper data, required tools and testing procedures were used to complete the modification. The potential gotcha is that few general shops have the kind of specialized equipment to do most major repairs by the book since it could include special tools, special jigs and special test equipment. We know plenty of cases where a designated engineering representative (DER) had to get involved because insufficient data was available-not uncommon on rare and vintage aircraft, for example. That generally costs thousands of dollars and you want to avoid that trap by doing the research before cracking a wrench.
For repairs, you might find more signing capability at a Part 145 repair station because the signed shop work order can often serve as the recording medium spelled out in Appendix B of Part 43. Still, not all Part 145 repair stations can do all major repairs under the Part 145 banner, but only those for which they have been approved by category. Still, a Part 145 shop has more latitude since they have been more carefully inspected by the FAA, and have training programs and written procedures and other requirements in place to assure quality work. Some repair stations even have special FAA approval to use methods and materials unique to their operation that the FAA feels is equal to or better than the factory manual method or parts.
Last, don’t underestimate the importance of having the proper paperwork to chase a major mod or repair because it could bite you when it comes time to sell the airplane. Supporting documentation-or the lack of-can make or break a deal.