The failure of the supervisor/ground controller and the local controller to provide effective separation between the accident airplanes on the runway, resulting in a collision during takeoff. Contributing to the accident was the failure of the pilot and pilot-rated passenger on board N79960 to ensure that the runway was clear of traffic before taxiing onto the runway. Also contributing to the accident was the failure of air traffic control guidance and procedures to incorporate redundant methods of verifying aircraft position for both controllers and pilots.