Originally Posted by JimC
What evidence do you have that contaminants in FBO fuel are causing problems in GA aircraft?
Fuel contamination in the US is not an issue.
I'm going through a CFII refresher, working on a ME add on, and NTSB accident statistics were presented for a decade ending in 2016 (the latest available as settling all causes takes about two years). The attached images are those relating to fuel. The black bar are fatal accidents.
There were two General Aviation accidents related to fuel contamination in that decade and I'm willing to bet that the fuel was not delivered that way. It is possible the contamination came after the fact from extreme condensation within the fuel tanks or an external source like rain or melting snow.
You are 15 times more likely to come up short with planning the fuel for a flight, I'd say especially with a 337 because of the inability to see into the tanks. Same with mismanaging the fuel load, there have been a number of these in pre-"G" Skymasters.
I think my recommendation of avoiding fuel contamination is the best bet. If you cannot see the lettering on a fuel hose, don't use it. If you need it, have the FBO provide a clean bucket and buy a gallon to run the "Clear & Bright" test yourself. That gallon will reveal any contaminants.
Aviation, these types of things, have always been self-policing, at least in this country. I don't have a problem letting the FBO know that they have sloppy practices.