Background
On the morning of the accident, Brown Field Municipal Airport (SDM) in San Diego, California, had parallel runways 8R/26L and 8L/26R. The air traffic control tower combined local and ground control positions, staffed by a local controller (LC) supervising a developmental controller (LC trainee) who transmitted instructions.
Sequence of Events
The Cessna 172 (N1285U) pilot requested touch-and-go landings in the VFR traffic pattern. Approximately 13 minutes before the collision, the LC trainee cleared N1285U for a touch-and-go on runway 26R, but the pilot executed a go-around and was advised to expect runway 26L. After completing a touch-and-go on runway 26L, N1285U entered a right downwind for runway 26R.
Meanwhile, the experimental North American Rockwell NA265-60SC Sabreliner (N442RM, call sign Eagle1) was 9 miles west of the airport, requesting a full-stop landing. The LC trainee instructed Eagle1 to enter a right downwind for runway 26R at or above 2,000 ft MSL.
ATC Communications
About 3 minutes before the collision, the qualified LC terminated training and took over radio communications. The LC then controlled nine aircraft. During the next 2 minutes, the LC made several errors, including failing to initially acknowledge a departure request, clearing an aircraft from a wrong runway, and correcting instructions to a helicopter pilot.
Approximately 1 minute before impact, Eagle1 reported downwind midfield and sighted traffic left and right. N1285U was to Eagle1's right, about 500 ft below. Mistaking N1285U for another Cessna (N6ZP) to the left, the LC instructed N6ZP to make a right 360° turn to rejoin the downwind. The N6ZP pilot acknowledged and began turning, but N1285U continued its approach. The LC did not visually confirm that N1285U was turning.
Ten seconds later, the LC instructed Eagle1 to turn base and land on runway 26R, placing the aircraft on a collision course. The LC then noticed the Cessna on downwind (still mistaken as N6ZP) had not turned, and contacted N6ZP, who responded that he was turning. The LC then transmitted to N1285U, which the pilot acknowledged, but the collision occurred as the LC tried to verify N1285U's position.
Collision and Investigation
N1285U and Eagle1 collided. Postaccident examination of both aircraft revealed no mechanical anomalies that would have prevented maneuvering to avoid impact.
Probable Cause
The local controller's (LC) failure to properly identify the aircraft in the pattern and to ensure control instructions provided to the intended Cessna on downwind were being performed before turning Eagle1 into its path for landing. Contributing to the LC's actions was his incomplete situational awareness when he took over communications from the LC trainee due to the high workload at the time of the accident. Contributing to the accident were the inherent limitations of the see-and-avoid concept, resulting in the inability of the pilots involved to take evasive action in time to avert the collision.