The autopilot was inadvertently engaged while taxiing to the departure runway. The pilot and his passenger attempted to disengage the autopilot by depressing the “A/P” button on the units control panel, but eventually turned off the avionics master switch to completely power down the unit. After reestablishing power to the avionics, the autopilot appeared disengaged. The pilot then attempted a takeoff but the airplane “prematurely” became airborne during the takeoff roll. The pilot immediately aborted the takeoff, but the airplane landed off the left side of the runway, impacting a snow bank and another runway before it came to rest nose-down. The nose landing gear had collapsed, causing substantial damage to the engine firewall.
