Synopsis
A Beech 95 (registration N9750Y) and a Cessna 180 (registration N42695) were involved in a mid-air collision while operating under visual flight rules (VFR) and receiving radar services from Stockton Terminal Radar Approach Control (TRACON). Both aircraft subsequently crashed in uncontrolled descents.
Sequence of Events
At the time of the accident, the Beech 95 was tracking south at approximately 185 knots, while the Cessna 180 was tracking 118 degrees at about 147 knots. Both aircraft reported an altitude of 5,500 feet MSL. The two aircraft converged and collided at approximately 5,500 feet MSL. Radar data indicated that N9750Y converged on N42695 from the northeast, about 70 degrees to the left of N42695's nose, while N42695 converged on N9750Y from the southwest, about 48 degrees to the right of N9750Y's nose.
The controller at the Tracy sector was occupied with coordinating two other aircraft that were operating under instrument flight rules (IFR) and required attention to maintain separation. The controller was not aware of the collision until later.
ATC and Radar Information
The collision occurred while the aircraft were receiving radar service under VFR flight following from Stockton TRACON during automated radar handoffs to the Tracy sector controller. The Stockton ARTS II radar system was not equipped with a conflict alert system. The ARTS II was programmed to move non-beacon (VFR) call signs to the tab list after not receiving a transponder reply for five scans (approximately 20 seconds). After an additional 33 scans (a total of approximately 2.5 minutes), the call sign would disappear from the tab list as well.