Airplanes are just like people; they have personalities, likes and dislikes, and as they get older they begin to fray a bit at the edges. And just like some people, when they are showing their age, they make a trip to aviation's answer to a plastic surgeon and get a makeover. The aviation makeover usually consists of a brand new shiny coat of paint, replacement of windows, state-of-the-art avionics package, and an interior to die for.
Interior makeovers come in all sizes and shapes, from expensive leather to the less expensive polyester, from imported teak wood table tops to Formica privacy doors on the privy. With all the options available it's really easy for mechanics to get a little confused and fall outside of the regulatory guidelines. I hope the following overview and review of certificate requirements for different type certificated aircraft will be helpful and help to reduce the interior confusion.
When replacing interiors, or just a couple of the interior's component parts, the Federal Aviation Regulations still require that the interior repair or alteration is airworthy. Just like we all learned in Aviation 101, "Airworthy means that the interior must meet its original type design or approved alteration and be in a condition for safe operation." Simply put, if you are going to put an interior in a Piper PA-28R-200 Arrow, then that interior must meet the same CAR-3 type design requirements that the PA-28 were type certificated under. If you are installing an interior in a Gulfstream IV, then that interior must meet the same FAR 25 type certificate requirements.
Airworthy's second requirement: "condition for safe operation" means that the new interior is designed in such a way that it can be inspected for wear and be maintained. Another way of looking at "condition for safe operation" is to ensure that on every flight the seats' locking pins, lock, and seat belts are securely attached and the VCR won't leave its rosewood cabinet in rough air and cold cock the vice president of accounting. Although not exactly an "airworthy requirement," a replacement interior should not be so poorly designed that it becomes a maintenance nightmare that consumes hundreds of man hours yearly to open up and reinstall just to perform required airframe inspections.
Interiors come in all shapes, sizes, and complexity. And it is usually the complexity of the interior work that determines if the alteration/repair is going to be major or minor. If the interior change is major, then approved data will be needed to make the mod. If it is a minor alteration or repair, then acceptable data is OK.
For example, if a major interior change guts the cabin, requires the addition of reinforced stringers, new wire bundles, and lead lined doubler plates to suppress the radiation from the nuclear powered port-a-potty the CEO wants installed, no one will argue with you that this is a major alteration and approved data is needed. But is it major or minor repair or alteration if just the soiled headliner, rug(s), and seats' fabric are being replaced?
With all things being equal and the headliner, seat fabric and rugs are being replaced on our Piper, and the replacement fabric and rugs are the same as the original, then the interior work is a minor repair. If the replacement fabric and rugs are different, say instead of the original type design 100 percent polyester fabric and rugs the new material is 80 percent wool and 20 percent polyester, and the new material meets the burn requirements of Part 23, then we have a minor alteration.
The same minor repair/alteration example would hold true if the same components were being replaced on a Gulfstream IV. These changes to the interior are either minor repairs or minor alterations because weight and balance, structural strength, performance, powerplant operation, or other qualities affecting airworthiness were not affected and the minor repair or alterations can be done by elementary operations (Ref: FAR-1 definitions of major repairs/major alterations).
In Part 2 of my tome on field approvals, we will cover current field approval policy found in Change 16 to FAA Order 8300.10.
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