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).
Now let's look at the material/fabric fire protection requirements for CAR-3 Certificated Aircraft.
These aircraft simultaneously make up both the oldest and majority of aircraft found in the U.S. aviation fleet. These are the Beech, Cessna, and Piper aircraft from days of our youth. The 10-year-old kids who hung on the airport fence in the late 1950s are now in their fifties and they are buying these older aircraft and revitalizing them in high hopes of recapturing their four decade old dream.
CAR-3 aircraft that are used for Part 91 operations, with interiors where smoking is not permitted, the interior materials shall be flash-resistant (Ref: CAR-3, Section 3.388). In CAR 3 aircraft interiors where smoking is permitted, the wall and ceiling linings, the covering of all upholstering, floors, and furnishings shall be flame-resistant (Ref: CAR-3, Section 3.388).
When a mechanic buys material in bulk to refurbish the interior, seats, and ceiling liners for a CAR-3 aircraft used in Part 91 operations, a manufacturer's statement declaring that the material meets the American Society for Testing and Materials (ASTM) or similar national standard for either flash resistance or flame resistance for the applicable installation would be acceptable. A manufacturer's statement is acceptable due to the fact that neither the old Civil Aeronautics Administration (CAA) or the Federal Aviation Administration (FAA) has not published an FAA fire standard for either flash or flame resistance for interior materials for CAR-3 aircraft. The FAA accepts and recognizes a national standard, so the mechanic who bought the fabric/material in bulk should reference the manufacturer's statement and the national standard that the fabric/material meets in the aircraft's maintenance records.
If no "standards" statement is made in the aircraft's logs, then the IA will have a problem at the aircraft's next annual inspection. He is looking at a new interior that may or may not meet CAR-3 requirements. In other words, he may have an "unapproved interior" and the fabric might have the flame resistance of a box of matches. So if the IA can't chase down the mechanic who installed the interior and get the necessary "standards" statement in the logbook, then the only other alternative he has, in order to solve this problem, is to have a laboratory check and certify that the fabric meets the ASTM or any other nationally-recognized flash or flame-resistant standard or do a burn test in accordance with Part 23, Appendix F.
A suggestion. To avoid mucking around with the flash/flame/burn federal requirements when you buy interior fabric/material in bulk for CAR-3 aircraft, the best way to satisfy the regulations is to have an appropriated FAA repair station perform and sign off a Part 23 burn test. If your fabric passes Appendix F requirements, then it exceeds the CAR-3, Section 3.88 requirements and you can tell your customers that they are better protected in case of an accident.
What about the fire protection for FAR -23/25 certificated aircraft interiors? Requirements for interiors for Part 23/25 are straightforward, none of this flash and flame duel CAR-3 standards. If you buy in bulk, the fabric and materials must meet Part 23, Appendix F or Part 25, Appendix F burn test requirements. The applicable Appendix F test must be performed by an FAA Repair Station who will certify that all materials and fabrics meet the regulation. This statement must be made part of the aircraft's maintenance records. If you buy interior fabric or materials that will be used on both Part 23 and Part 25 aircraft be sure that the repair station certifies that the material/fabric meets both Part 23 and Part 25 requirements.
If a CAR 3, Part 23, or Part 25 aircraft has an interior installed under a STC, then the new interior is considered a major alteration and the STC number must be noted on Block 8 of the FAA Form 337 and in the aircraft's maintenance records. It is not necessary to state in the aircraft's maintenance logbooks that the interior meets burn requirements of Appendix F of either Part 23 or Part 25. The fact that the STC is FAA-approved data satisfies the burn test requirement. Also, don't forget that under the new law passed by Congress in October of 1996, the owner of the aircraft must have a letter from the STC holder that authorizes the owner to install the STC.
Some Things to consider
A few suggestions that as a mechanic or repair station that are into remods should consider are:
1. Keep copies of all flash/flame/burn tests and certifications with the bulk fabric/materials you have in stock and a copy in a secure place, just in case you are asked by your friendly FAA inspector.
2. Keep samples of fabric and material and their invoice numbers used in the aircraft's interior modifications so replacement is a snap vs. a chore.
3. Be careful of dry cleaning chemicals/soaps/detergents that are used to clean interiors. They can degrade the fire protection of the fabric. Remember on CAR-3, Part 23, and Part 25 aircraft the flash/flame and burn requirements are part of the aircraft's type design. If a mechanic suspects that the interior no longer meets the rule, then samples of the interior fabric should be tested.
4. If your company recently bought a Part 23/25 aircraft or if your company is considering a purchase of a used aircraft, then a burn test of the interior materials is strongly recommended.
How are interiors approved? If you want to completely redo your aircraft's interior, add a wet bar, entertainment center, phones, etc., we are talking a major alteration here. Any major alteration requires approved data. The three ways where you can get approved data are: have a designated engineering representative draw up and approve the data, the STC route, and FAA field approval. A word here about field approvals. FAA inspectors are not in the business to compete with DER or holders of STC. We will do field approvals for the addition of equipment like a TV or a sound system, but full remod of interiors are big projects and literally will take up too much of our time, so a DER or an STC should be your first choice.
FAA repair stations also have an option of taking DER-approved data and making it into a process specification approved under the repair station's operating limitations. For example, Poteen's aviation interiors, a FAA Part 145 repair station has an order from a Learjet operator to remod six of their jets. Since the interiors are all the same, the DER information can be made part of the repair stations' process specifications. The process specifications can be enlarged to cover recordkeeping, Instructions for Continued Airworthiness, and replacement of parts.
Aircraft interior installation and maintenance is perhaps one of the most overlooked components found on an aircraft. The NTSB accident data tells us that many people survive the initial accident, yet many die, because of smoke and fire-related injuries caused by the fires that fed on the aircraft's interior or failure of interior components. I have personally been at accidents where individual(s) have been fatally injured because of something simple like a handheld fire extinguisher was improperly secured and became a lethal missile propelled by the force of impact or a seat belt failed because its corroded attachment bolt was hard to inspect because it was hidden by the interior panel.