After pulling the aircraft of the hangar with his automobile due to ice and snow covered ramps; the pilot of an SR22 fails to remove towbar from the aircraft prior to takeoff.

Narrative

I was preparing to depart on a Part 91 positioning flight to pick up passengers for a Part 135 air taxi flight. It was over 1 hour before sunrise so I performed the preflight inspection inside the warm; lighted hangar instead of outside on the completely unlighted ramp. Other than the towbar still being attached to the nosewheel; the plane was ready. My normal procedure is to pull the plane out of the hangar by hand and stow the towbar in the baggage compartment. On this day; though; the ramp was covered with ice and snow and I didn't even attempt to pull it out by hand. Instead; I backed my car up to the airplane; attached the towbar to the car and slowly pulled the plane out of the hangar. I got out of the car; closed the hangar; disconnected the towbar from the car (but NOT from the airplane) and moved my car from the ramp to the parking area. I then went to a different hangar to use the restroom; then walked back across the still-dark ramp to the plane. I 'knew' that the preflight was done; so I got into the plane; started up; taxied and departed. Upon landing after the 20-minute flight; the Tower Controller advised that I appeared to have a fire underneath the airplane. I immediately killed the boost pump and pulled the mixture; coasted to the nearest taxiway; and exited the airplane. There was no evidence of a fire or even of excessive heat. There was; however; the remains of the towbar still attached to the nosewheel and trailing behind it; and ground down where it had been pressed against the runway on landing. This obviously sent up a shower of sparks which is what the Controller had seen. The main cause of the problem was my failure to do one last walkaround of the airplane (with a flashlight!) before departure. Contributing to the problem was the introduction of a nonstandard procedure -- using the car to pull the plane out of the hangar -- which interrupted my normal sequence of events. Another contributor was the ice and crunchy snow covering the ramp. While taxiing; there were so many unusual sounds that I did not hear the towbar dragging across the pavement. In the future; my standard procedure will be to make one complete walkaround of the airplane before entering -- always -- even if the preflight has been completed In addition; my standard procedure will include leaving the aircraft keys in the baggage compartment door lock any time the towbar is out of the baggage compartment. This isn't foolproof; of course; but it would help.