What happened
On March 20, 2003, between 12:18 and 12:20 UTC, a separation loss occurred between a military MiG 21 (registration SSR A2451) and a civil Boeing 747 operating flight SIA025. The incident took place within the TSA 60 airspace at flight level 310.
The civil Boeing 747 was operating a scheduled flight from Frankfurt (EDDF) to Singapore (WSSS) via airway UL 984. During the flight, the military MiG 2/1, which was part of a pair performing a mission for the NATINEADS readiness system, approached the civil aircraft from the north in a descending flight. The military aircraft passed the Boeing 747 at the same altitude before turning west. At the time of the encounter, the separation between the two aircraft was less than 4NM. The crew of the Boeing 747 reported the situation to Prague ACC, noting that the TCAS alert had not been triggered.
The investigation
A joint commission comprising representatives from the ÚZPLN and the Czech Air Force (AČR) investigated the incident. The investigation examined radar records, including the Short Term Conflict Alert (STCA) data, and reviewed the communications between the military aircraft and the combat use radar controller.
Investigators found that the military aircraft pair had split up at 12:18 UTC. While the first aircraft continued on a course of 270°, the second aircraft performed a maneuver involving a course of 180° followed by a turn to 270°. During this maneuver, the second aircraft entered a descent and exited the TSA 60 airspace.
Findings
- The combat use radar controller failed to intervene when the second military aircraft approached the southern boundary of the TSA 60 airspace.
- The radar controller did not monitor the aircraft's descent because Mode C altitude information was unavailable and air defense radar altitude data was not being utilized.
- The pilot of the second military aircraft was not informed of approaching traffic upon inquiry; instead, information regarding departing traffic was provided.
- The phraseology used in communications between the military aircraft and the combat use radar controller did not comply with established tactical aviation procedures.
- The military controllers failed to adequately account for the proximity of international airways and the potential for contact with civil traffic, thereby compromising aviation safety.
Safety action
Following the investigation, it was recommended that both military and civil aviation authorities increase their attention to the shared use of airspace. The Czech Air Force command was tasked with ensuring that combat use radar controllers are briefed on the incident and to implement internal measures within their jurisdiction.