On June 25, 2005, at 1410 eastern daylight time, a Piper PA-28-180, N8321W, impacted a Martin Sonex, N569SX, during an on-ground collision at Padgham Field Airport, Allegan, Michigan. Both airplanes were awaiting takeoff clearance when the Piper PA-28-180 rolled forward while stopped on a taxiway and impacted the Martin Sonex. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 91 personal/educational flight was a Experimental Aviation Association's Young Eagles program flight. Neither airplane was operating on a flight plan. The airline transport pilot and three passengers aboard the Piper PA-28-180 were uninjured. The pilot aboard the Martin Sonex was uninjured. The pilot of the Piper PA-28-180 stated that he was holding in position when he became distracted from holding the brakes while leaning across his right seat passenger to secure the entry door. The airplane then rolled and struck the left horizontal stabilizer and elevator of the Martin Sonex with his propeller. He stated that they taxied with the door open because of the extreme heat and lack cabin air circulation. The 1965 Piper PA-28-180, serial number 28-2496, was registered to the pilot as co-owner on February 27, 2004. The airplane was not certificated nor equipped with shoulder harnesses. Advisory Circular 91-65, Use of Shoulder Harness in Passenger Seats, states: "...The safety board [National Transportation Safety Board] found that 20 percent of the fatally injured occupants in these accidents could have survived with shoulder harnesses (assuming the seat belt fastened) and 88 percent of the seriously injured could have had significantly less severe injuries with the use of shoulder harnesses. Energy absorbing seats could have benefited 34 percent of the seriously injuries. The safety board concluded that shoulder harness use is the most effective way of reducing fatalities and serious injuries in general aviation accidents."