Incident Overview
On an unspecified date, a midair collision occurred approximately 2.8 miles west of Palo Alto Airport (PAO). The aircraft involved were a Cessna 152, registration N152SC, and a Mooney M20J, registration N5201Y. N152SC was executing a left crosswind departure from runway 30. N5201Y, on a traffic watch flight for a local radio station, was transiting the airport traffic area (ATA) from southeast to northwest and descending from 2,400 to 1,500 feet. Both pilots were able to land their aircraft safely after the collision.
Air Traffic Control Actions
The local control position at Palo Alto was staffed by a developmental controller under the supervision of the tower supervisor. The developmental controller had eight hours of on-the-job training in that position. He did not identify N5201Y on his bright radar display. The supervisor observed a potential conflict developing and waited a few seconds before issuing an advisory, hoping the developmental controller would identify and resolve the situation. The supervisor then transmitted a traffic advisory to N152SC, but received no reply. Approximately nine seconds later, the two aircraft converged and collided.
Airspace and Traffic Conditions
The airspace in the area was complex, with five airport traffic areas adjoining each other. The variable floor segments of the Terminal Control Area (TCA) ranged from 4,000 feet over Palo Alto to 1,500 feet over San Carlos. N5201Y had just been given a frequency change to San Carlos Tower to transit its ATA, which was adjacent to the Palo Alto ATA. N152SC was on the Palo Alto tower frequency.
Pilot Actions
Neither pilot saw the other aircraft in time to avoid the collision. Despite the collision, both pilots retained control and landed safely.