On Saturday, August 21, 1993, at 0650 hours mountain standard time, an Ultimate 10-80 ultralight aircraft, N51677, collided with an ultralight RX-550 aircraft, N38RJ, on the approach threshold of runway 35, at Stellar Airpark, Chandler, Arizona. The pilot of the Ultimate 10-80, N51677, was completing a local visual flight rules personal flight; the pilot of N38RJ was beginning a local visual flight rules personal flight. Both aircraft sustained substantial damage. The certificated private pilot aboard N51677, the sole occupant, was not injured; the noncertificated pilot aboard N38RJ, the sole occupant, sustained serious injuries. N51677 flight originated at Stellar Airpark at 0600 hours. The pilot of N51677 told Mr. Paul Texter, aviation safety inspector, Federal Aviation Administration (FAA), Phoenix [Arizona] Certificate Management Office, that he observed N38RJ taxiing toward the runway. He also stated that he announced his location on 122.8 MHz, the common traffic advisory frequency (CTAF). The pilot also stated that he heard and felt the collision with N38RJ as the aircraft crossed the landing threshold. He then stated that the design of the Ultimate 10-80 restricts the forward and downward vision of the aircraft. The pilot reiterated his statement to Inspector Texter in the Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1/2, submitted by the pilot of N51677. He stated that due to wires crossing the final approach course he was required to fly at slow airspeed with a high angle of attack and a high sink rate. N38RJ had stopped at the runway threshold/taxiway intersection when he turned onto the final approach. Examination of N38RJ revealed that the airplane was not equipped with any two-way radio communications. The pilot of N38RJ was immediately transported to the hospital and was not available to be interviewed. The pilot did not respond to the Safety Board's request to complete the required Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1/2. According to the FAA, Airman's Record Section, the pilot of N38RJ does not hold any pilot or medical certificate. Federal Air Regulations require any person who operates a registered civil aircraft to hold a pilot certificate for that category and class of aircraft; a properly endorsed student pilot certificate would be acceptable. The regulations also require that the pilot hold a valid medical certificate appropriate to the operation being conducted. Title 14 CFR Part 91.113(b) states: General - When weather conditions permit, regardless of whether an operation is conducted under instrument flight rules or visual flight rules, vigilance shall be maintained by each person operating an aircraft so as to see and avoid other aircraft. When a rule of this section gives another aircraft the right-of-way, the pilot shall give way to that aircraft and may not pass over, under, or ahead of it unless well clear. Title 14 CFR 91.113(g) states, in part: Landing - Aircraft, while on final approach to land or while landing, have the right-of-way over other aircraft in flight or operating on the surface, except that they shall not take advantage of this rule to force an aircraft off the runway surface which has already landed and is attempting to make way for an aircraft on final approach.