Incident Overview
A Cessna 525 and a Cessna 172 collided in flight at approximately 3,400 feet mean sea level while on converging courses. The Cessna 525 was heading north, and the Cessna 172 was heading southwest. The closing speed between the two aircraft was about 300 knots.
Flight Details
The Cessna 525 had departed under instrument flight rules and was receiving vectors from air traffic control. The pilot was initiating a climb on course when the collision occurred. The pilot had acknowledged a climb clearance from terminal approach control, but the acknowledgement was interrupted by the impact.
The Cessna 172 had departed from a local airfield located just outside the 30-mile Mode C veil airspace of a terminal airport and was proceeding southwest. The collision happened as the 172 was approaching the Class D airspace of a military tower, and its pilot was initiating radio contact with that tower.
Air Traffic Control and Equipment
The terminal approach controller in contact with the Cessna 525 stated that he did not observe the primary radar target of the Cessna 172. Conflict alert software was not installed in the radar system. The Cessna 172 did not display a transponder signal; the transponder switch was subsequently found in the off position.
Cockpit Visibility
A cockpit visibility study indicated that from a fixed eye position in the Cessna 525, the Cessna 172 was essentially hidden behind aircraft structure for the 125 seconds before impact. The 172 could be seen by shifting the pilot's eye position. From the Cessna 172, the 525 was viewable in the left lower section of the windscreen.
Operational Conditions
Both airplanes were operating in visual flight conditions. Training in the Cessna 525 emphasizes maximum use of the autopilot to allow greater outside scanning by the single pilot. The autopilot controller is located at the rear of the cockpit center-mounted pedestal.
Probable Cause
The failure of both pilots to see and avoid conflicting traffic, and the failure of the 172 pilot to operate the transponder as required by current regulations. Factors were the controller's failure to observe the traffic conflict, the lack of radar conflict alert capability, and the training emphasis on maximum autopilot usage with the autopilot controller placed at the rear of the cockpit center mounted pedestal.