NOTE: SPECIAL CONDITIONS are issued in accordance with 14CFR §21.16 - If the Administrator finds that the airworthiness regulations of this subchapter do not contain adequate or appropriate safety standards for an aircraft, aircraft engine, or propeller because of a novel or unusual design feature of the aircraft, aircraft engine or propeller, he prescribes special conditions and amendments thereto for the product. The special conditions are issued in accordance with Part 11 of this chapter and contain such safety standards for the aircraft, aircraft engine or propeller as the Administrator finds necessary to establish a level of safety equivalent to that established in the regulations.
Two experienced engineers - each with more than twenty years of Composite Materials experience (Lockheed and Boeing) submitted comments to the NPRM. It was their comments that caused us to investigate the SAFETY OF COMPOSITES IN PASSENGER AIRPLANES! Their comments and the FAA’ s response will be the subject of the next NEWSLETTER, but as an Aviation Safety Specialist at the Scottsdale FSDO used to say . . . Jim, I’m not very comfortable with that - meaning he didn’t think my solution to a problem would cover all the regulatory requirements.
Well, I’m not comfortable at all, but let’s look at the FAA document that is supposed to address the problem both the experts were concerned about - a low speed takeoff or landing accident - usually survivable in a “tin airplane” - spilled fuel - and holes in the fuselage. But before...
The FAA’s recommended practice for burnthrough protection is --
Advisory Circular 25.856.2A -
INSTALLATION OF THERMAL/ACOUSTIC INSULATION FOR BURNTHROUGH PROTECTION. (To protect the folks inside the airplane)
“6. EXPLANATION OF TERMS.
a. Burnthrough. The penetration of an external fire into the airplane cabin, typically through the airplane skin, insulation, and sidewall or floor structure. For the purposes of the test, a breach of 0.25” or more in diameter is considered burnthrough.
b. Overlap. The length of insulation material that presents a double thickness of material either against the airplane skin, for the purposes of joining two bags, or abutting airframe structure other than the fuselage skin (see figure 1).
c. Pool Fire. An extensive ground fire originating from fuel spillage from damaged airplane fuel tanks.
d. Thermal/Acoustic Liner. Any materials (for example, a blanket) that are used to thermally or acoustically insulate the interior of the airplane. These materials are typically installed onto the airplane skin or other structure and can form a barrier between the passenger cabin and an external fire. Thermal/acoustic liners consisting of batting encapsulated by a moisture barrier may be known as “bags.”
e. Field Blanket: Thermal/acoustic liner positioned between structural members (frames, for example) and typically fastened on the liner’s periphery.
f. Lower Half: The area of the fuselage below the horizontal line that bisects the cross section of the fuselage. This may be determined using the height of the fuselage as a basis.”
Do you think this is a valid solution?
THE WORD COMPOSITES DOES NOT APPEAR IN THE AIRWORTHINESS STANDARDS FOR TRANSPORT CATEGORY AIRCRAFT - PART 25 . . . BUT IT DOES IN THE THREE OTHER AIRWORTHINESS STANDARDS -
(Part 23 Normal . . . and both helicopter Parts - 27 & 29). If you want the "official words" on FIRE, SMOKE AND TOXICITY you have to google FAA’s Atlantic City Research Facility - Home of the Fire Safety Branch. If you read the "stuf" they have prepared for "fire fighters" - the dangers of composite fires - you wouldn’t want to be near a burning composite airplane. Yes, an innocent overheated brake on a Cirrus light plane can "melt" the wing and . . . . .Cirrus uses wet wings rather than an aluminum fuel tank tucked inside the wing. So any crack in the plastic from an accident turns into a fuel leak, and the planes have had a tendency to catch on fire after crashing. By the way, you don’t have to crash a Cirrus to melt the wing . . . .remember, a simple brake fire will do it! More on simple wheel fires and the Australian Aircraft Fire Fighting Proceures coming soon.
Posted for Jim