My aircraft’s, a 1966 Piper Cherokee PA28-180C, Flight Manual states that the fuel must be “91/96 minimum octane aviation fuel.” Does this mean any aviation fuel of the required octane, such as Swift’s 94UL is acceptable or must I still have a STC?
Lycoming Service Instruction 1070AB authorizes the use of 94UL in many of their engines. That manufacturer's authorization is sufficient. And the O-360-A-series is on the list of engines approved for both 91UL and 94UL when they meet ASTM standard D7547.
I had read 1070AB, but as stated in the CAUTION statement, “airframe approval is required.” So my question should be, since Lycoming has approved my O360 for alternate fuels, does the statement in the Flight Manual allow their use in my airframe?
That's my read.
No. The airframe approval comes from the Swift Fuels UL94 STC for the Piper PA-28-180. Go to
If the airframe manufacturer has already approved something, you do not need an STC for that something. The AFM pictured above certainly seems to approve any “aviation fuel” of at least 91/96 octane, which 94UL is. If you have something from the FAA that says otherwise, I'd love to see it.
Now, my Grumman Tiger's AFM says “minimum 100 octane”, so I'll have to pony up my $100 for the Swift STC. But that's only because my Tiger's limitations say 100 minimum, and further says only 100/130 green or 100LL blue, so I'll need another STC for 100UL when it becomes available.