Hello,
I have been playing starflight one, a blast down memory lane. I noticed that I'm not using any endurium. What could cause that? I know that I used it on the original floppy disk for landing and taking off from planets.

Are you only landing on really low gravity worlds? I think the game rounds down the fuel usage in that case to 0.

I've had several trips around the starting solar system, I've yet to use any fuel. it is strange, never noticed this behavior before.

Endurium is used only by the warp nacelles during inter-stellar flight, IIRC; in-system exploration is powered by magnetically energized impulse engines deriving power from the magneto fields of system planets & suns, thus no Endurium is expended during in-system flight.

Not strictly true. If you land on a large world with high G you might need to use fuel to lift off. I've had this situation in game. I landed on a large-ish world, disembarked and poked around a bit. Embarked again and went to take off only to be told you don't have enough fuel for that. I had to activate the emergency beacon to get back to Arth. Obviously the planet wasn't too massive or the ship would have been crushed, but my fuel reserves were on the low side. Maybe 8 units or so...enough to get back to Arth....if I'd been able to take off.