Background
On an unspecified date, a Mooney and a Beech aircraft collided in midair while on the downwind leg for right traffic to runway 24 at Palomar Airport. The air traffic control tower was equipped with a digital bright radar indicator tower equipment (DBRITE) radar system.
Sequence of Events
At 1247, a pilot in the Beech contacted Palomar ground control (GC) to request taxi from its fixed base operator (FBO) to runway 24. The pilot of the Mooney called Palomar tower at 1255:37, reporting a position 10 miles north of the airport for landing. The local controller (LC) instructed the Mooney pilot to enter right traffic for runway 24 and to report downwind.
The LC stated that the DBRITE location in the cab placed it out of the line of sight of the majority of her traffic scan, so using the DBRITE for reference required diverting her attention from the traffic in the pattern and on the runway. She observed the Mooney's identity next to its target on the DBRITE, placed the Mooney on the arrival list, and continued working other traffic.
Radar data indicated that the Mooney's target followed the coastline from Oceanside to a point about 3 miles northwest of Palomar, then turned eastbound and tracked toward the right downwind leg for runway 24. At 1258:08, the LC cleared the Beech for takeoff, and the pilot acknowledged. The Beech's first radar target appeared at 1258:39, and the airplane passed the departure end of the runway at 1259:02. The Beech immediately turned right crosswind.
At 1259:27, the LC transmitted a traffic advisory to the Mooney, advising of the Beech on right crosswind turning to downwind, and also advised the Beech pilot of the Mooney traffic inbound on the 45-degree entry to downwind. There was no response from either airplane. According to the LC, the airplanes collided immediately after this transmission.
At 1259:36, the Mooney radar target crossed the path of the Beech target, at a mode C reported altitude of 1,300 feet mean sea level (msl), and the two targets merged. Measurement on the plot determined that the convergence angle was 124 degrees.
Witness Observations
One witness observed the Mooney, which was light brown with dark brown accents, bank to the right immediately prior to impact. Another witness reported that both airplanes appeared to turn at the last second, but both turned the same way into each other. Witnesses reported seeing the two airplanes merge, followed by a puff of white smoke. A piece of wing fell from the Mooney, and the airplane immediately entered a nosedive, striking the ground at 1259:43, approximately 300 yards from the estimated collision point.
The Beech, which was white with blue accents, banked left and maintained that attitude for a few seconds. To some witnesses, the bank angle approached 90 degrees, while to others it appeared to go to an inverted position. The nose-down attitude became steeper until it nosed vertically into the ground. The airplane landed about 100 yards from one witness, who did not observe any attempts at recovery. The last radar target, received at 1259:48, showed the airplane descending through a mode C reported altitude of 500 feet.
Investigation Findings
During the period that the Beech was taxiing, the ground controller characterized the LC's workload as light to moderate, with no unusual circumstances in the traffic pattern. There were "a few" clouds west of the airport that were close enough to be a factor for departures; they could cause pilots to turn somewhat earlier than normal if necessary to maintain adequate clearance.
Evaluation of all evidence determined that the conflict was detectable both visually and on the tower radar display. When the LC realized that they were in conflict, her actions were too late to provide the pilots with adequate time to maneuver to avoid a collision. The local controller's loss of situational awareness contributed to the accident.
FAA Order 7110.65 "Air Traffic Control" prescribed ATC procedures and phraseology. Paragraph 3-1-1 instructed controllers to provide airport traffic control service based only upon observed or known traffic and airport conditions. A note stated that when operating in accordance with the Code of Federal Regulations, it was the responsibility of the pilot to avoid collision with other aircraft, and that due to limited space around terminal locations, traffic information could aid pilots in avoiding collisions.