4 ms·

I suspect what needs to happen is that someone (ASTM?) comes up with a spec for unleaded 100 octane avgas, and then the FAA can give a blanket approval for that

by jabl 3y ago

I suspect what needs to happen is that someone (ASTM?) comes up with a spec for unleaded 100 octane avgas, and then the FAA can give a blanket approval for that spec for any plane certified for 100LL.

sokoloff 3y ago
Can't (realistically) be done. The specification for most airplane engines say "100LL" and the specification for 100LL is a composition specification (ASTM D 910), not a performance specification. If your fuel meets ASTM D 910, it contains lead. If it doesn't contain lead, it doesn't meet ASTM D 910 and therefore definitionally isn't 100LL, so if your engine type certificate data sheet calls for 100LL, it unavoidably calls for lead. If you are flying an aircraft that is thus-certified, flying it with a different fuel is, per the FAA definition in 14CFR3.5, flying an unairworthy airplane. "Airworthy means the aircraft conforms to its type design and is in a condition for safe operation." That's the legal reasoning that the Gami STC is required: to change the TCDS of the engine and airframe to permit a fuel other than 100LL and still be considered airworthy. (The STC process is totally workable and, IMO, doesn't need to be "fixed" and Gami has basically done the work you're asking to be done AFAICT.)
- jabl 3y ago
  Weren't many of the planes in operation today certified before 100LL became the only available grade (excluding things like 115/145 or even more exotic brews which I guess today are used only at Reno air races and such)? E.g. 80/87 for lower performance engines, and 100/130 for higher performance ones. So presumably they were somehow grandfathered in when 100LL replaced these grades? So why can't the same be done for a hypothetical "100UL" spec?
  - sokoloff 3y ago
    Based on the type certificates for the common airplanes and engines I looked at, the type certificates were re-issued with 100LL as an/the approved fuel under the type design. (This would be done after testing as required by FAA.) That’s what the STC process does legally, just being done by the engine/airframe manufacturer instead of third party (presumably because they wanted to continue selling engines/airframes).

by jabl 3y ago

sokoloff 3y ago

Can't (realistically) be done. The specification for most airplane engines say "100LL" and the specification for 100LL is a composition specification (ASTM D 910), not a performance specification. If your fuel meets ASTM D 910, it contains lead. If it doesn't contain lead, it doesn't meet ASTM D 910 and therefore definitionally isn't 100LL, so if your engine type certificate data sheet calls for 100LL, it unavoidably calls for lead. If you are flying an aircraft that is thus-certified, flying it with a different fuel is, per the FAA definition in 14CFR3.5, flying an unairworthy airplane. "Airworthy means the aircraft conforms to its type design and is in a condition for safe operation." That's the legal reasoning that the Gami STC is required: to change the TCDS of the engine and airframe to permit a fuel other than 100LL and still be considered airworthy. (The STC process is totally workable and, IMO, doesn't need to be "fixed" and Gami has basically done the work you're asking to be done AFAICT.)

jabl 3y ago
Weren't many of the planes in operation today certified before 100LL became the only available grade (excluding things like 115/145 or even more exotic brews which I guess today are used only at Reno air races and such)? E.g. 80/87 for lower performance engines, and 100/130 for higher performance ones. So presumably they were somehow grandfathered in when 100LL replaced these grades? So why can't the same be done for a hypothetical "100UL" spec?
- sokoloff 3y ago
  Based on the type certificates for the common airplanes and engines I looked at, the type certificates were re-issued with 100LL as an/the approved fuel under the type design. (This would be done after testing as required by FAA.) That’s what the STC process does legally, just being done by the engine/airframe manufacturer instead of third party (presumably because they wanted to continue selling engines/airframes).