On November 15, 1993, at about 0718 eastern standard time, a Piper PA-60, N91WW, registered to Cherokee Leasing Inc., operating as a 14 CFR part 135 on-demand air taxi flight collided with a Cessna 172, N1753V, registered to Flight Express Inc., operating as a 14 CFR part 91 aerial observation flight, while taxiing. Both airplanes sustained substantial damage. Both commercial pilots and one passenger in the Cessna 172 were not injured. Visual meteorological conditions prevailed. An IFR flight plan was filed by the Cherokee Express pilot, and no flight plan was filed by the Flight Express pilot. Both flights were originating at Orlando Executive Airport. The pilot-in-command of the Cherokee Express airplane stated in an interview with the NTSB investigator-in-charge that he observed two Cessna airplanes in the runup area for runway 07 as he was taxiing to the same runup area. The Cessna airplanes had their engines running, and were parked one behind the other. Upon entering the runup area the pilot stated there was some ground fog and the sun was directly in his eyes. The pilot observed a Cessna airplane which he thought was the front airplane, which in reality was the rear airplane. He continued to turn and collided with the airplane. The pilot-in-command of the Flight Express airplane stated in a written statement, I was parked in the ramp area waiting for takeoff clearance clear of taxiway golf. I heard an engine that sounded like it was doing a runup. I saw an Aerostar coming right at me. I saw the pilot looking down and the left prop coming right for my left wing and fuel tank. At this time I tried to move away from the Aerostar to prevent impact. The Aerostar never stopped and ran right into me. The nearest weather reporting facility at the time of the accident was on the Orlando Executive Airport, Orlando, Florida. There were no reported restrictions to visibility at the time of the accident. Review of sun and moon information for the Orlando Executive Airport, revealed official sunrise was at 06:52.