What happened
On January 28, 2008, at 13:55 UTC, two aircraft were performing circuit operations at Cascais Aerodrome (LPCS). The first aircraft, a Cessna 172, registration CS-ASU, was conducting a training flight consisting of landings and takeoffs. The second aircraft, a Cessna 152, registration CS-AVC, was conducting a flight instruction session with an instructor and a student pilot.
During its third circuit, the CS-ASU performed a touch-and-go landing. Shortly after, the CS-AVC departed the runway. The air traffic controller, who was simultaneously managing both the Tower and Ground positions, was aware that the CS-AVC intended to join the traffic pattern, as this information had been communicated on the Ground frequency. However, this information was not relayed to the pilot of the CS-A SU, who was monitoring the Tower frequency.
Unaware that the CS-AVC would be joining the circuit, the pilot of the CS-ASU began a turn to the downwind leg while climbing. In doing so, the pilot cut across the circuit, passing approximately 200 feet below and 300 meters ahead of the CS-AVC. This maneuver forced the CS-AVC to widen its turn to maintain separation. Following the incident, the controller instructed the CS-ASU to perform an immediate final approach and land.
The investigation
The GPIAAF investigation examined the flight paths, the controller's communications, and the adherence to standard operating procedures. The investigation established that the controller possessed information regarding the intentions of the CS-AVC via the Ground frequency but failed to disseminate this information to the CS-ASU, as required by international standards. Furthermore, the investigation looked into the pilot's decision to shorten the circuit and the controller's subsequent instruction to the pilot to land immediately.