Incident Overview
On 11 March 2011 at approximately 11:37 UTC, two Cessna 172 aircraft operating under Visual Flight Rules (VFR) encountered a loss of separation near Famalicão, Portugal. Both aircraft were conducting instructional flights under the operator Nortávia. The incident occurred in Class G airspace, where air traffic control services are limited. No injuries or damage were reported.
Aircraft and Crew Information
The first aircraft, a Cessna 172R (registration CS-DGM, serial number 80548), departed from Porto Airport (LPPR) with one instructor and two student pilots on board. The second aircraft, a Cessna 172N (registration CS-DCU, serial number 67812), departed from Maia Municipal Aerodrome (LPVL) with one instructor and one student pilot.
Sequence of Events
The CS-DGM departed at 10:01 UTC and proceeded to the Guimarães training area, initially cleared to operate between 2,000 and 3,000 feet. At 11:20, the Porto Approach instructed CS-DGM to maintain 2,000 feet or below, a restriction lifted at 11:28 when it was again authorized to operate between 2,000 and 3,000 feet.
The CS-DCU departed at 11:01 UTC and proceeded to the Santo Tirso training area, cleared to operate between 2,000 and 3,000 feet. At 11:26, it was instructed to maintain 2,000 feet or below; this restriction was lifted at 11:30, with authorization to operate between 2,000 and 3,000 feet.
At 11:37 UTC, the two aircraft converged approximately 3 nautical miles northeast of Santo Tirso, with a lateral separation of about 0.5 nautical miles and a vertical separation of 200 to 300 feet. Neither aircraft had been informed of the other's presence. When CS-DCU requested traffic information at 11:37, the controller reported CS-DGM's presence, though it was not visible on radar at that moment. The controller then instructed CS-DGM to move further east due to traffic.
Airspace and Services
The incident occurred in Class G airspace, where air traffic control provides only basic services. The specific classification of airspace and the services provided are governed by ICAO Annex 11. The investigation noted that air traffic control services include flight information, air traffic control (for controlled airspace), and alerting services. In Class G, VFR flights are not separated by ATC; however, controllers may issue traffic information and instructions to enhance safety.
The investigation concluded that the event met the criteria for classification as a serious incident as per ICAO Annex 13 Appendix C and Portuguese decree law.