TIL. There's still a problem that running the engine till fuel starvation is not exactly a practical option, but then arguably you could make it so that standa

TIL. There's still a problem that running the engine till fuel starvation is not exactly a practical option, but then arguably you could make it so that standard shut down depended on at-tank cut off valve (going to make certification a PITA). And of course you can't reuse original fuel runs because for majority of aircraft, the tank won't fit where existing tanks are. I'm still unconvinced that you could avoid considerable reconstruction of the fuel lines - there are reasons why propane/LPG have different hazard classification, and what is easily allowed on a ground vehicle can be a big nope in an airplane. On the more practical side, it would be dead in the water from legal issues - you'd have to recertify the plane, possibly deal with the fact that there's AFAIK no preexisting baseline for certification, and unlike 100UL you'd also add pilot & mechanic retraining - at this point you might have better ROI by shooting for the stars and going the cryogenic hydrogen route. While there are some CNG & LPG conversions around, pretty much everything seems to fall under experimental classification - something wildly different from the goal of getting G100UL declared fully equivalent to AVGAS 100LL, which would allow everyone to just switch supply.