A few questions. One, sometimes when I tell my Toads to "attack area" they will fly in a straight line very slowly and won't respond to any of my orders. Any ideas why this happens?

Also, is there any way to tell how much fuel an aircraft has? I could be missing something completely obvious, but I can't seem to find a way to know.

Finally, in the case of aircraft refueling, what determines whether they will land near the landing pad when they are done refueling, and what determines whether they will return to their previous missions? I'm still kind of a noob to NOTA but it seems like patrolling aircraft will return to their patrol after refuel, but I can't tell about anything else (for instance, if I tell bombers to attack a target, if they lose fuel on the way, they seem to go back, refuel, and land next to the pad rather than continue to attack the target).

Fuel is shown with hitpoints and other stats in the bottom left when they are selected. All aircraft are supposed return to doing whatever they were doing after refueling, but the bombers do seem to lose their attack orders, as you said. I think this bug was introduced last spring version. Unfortunately all the fuel stuff is hardcoded into the spring engine. I don't know about the toads, I don't think I've seen them do that.

Planes will wait in line to refuel if there are no free pads when they turn back for fuel. If you build more pads after the bombers have joined a waiting line you can tell them to refuel which will look for the fastest refuel, not waiting for the original pad to clear.

Last night in a game, I had a few fighters patrolling, and when they ran out of fuel, they just landed. There were free refuel pads at my own and an ally's base, and when I told them to refuel, they did. How come they didn't do this automatically?

That was an engine bug. It is fixed.