What happened
On February 4, 2008, a Ventus C glider, registration OK-1834, entered the controlled airspace of FIR Praha (Class C) without the required flight clearance. The pilot had departed from Jelenia Gora (EPJG) and intended to fly a route through Šluknov. Although the pilot had submitted a flight plan the previous day, he incorrectly entered "VFR" in the altitude field, which indicated a flight level of only 1,000 feet AGL. Because of this entry, the flight plan was not forwarded to the Area Control Center (ACC).
During the flight, the pilot climbed to approximately 4,360 meters. At approximately 08:42 UTC, the pilot attempted to establish contact with Prague Radar using the Southeast sector frequency. The controller responded in English, and the pilot communicated in Czech. The controller instructed the pilot to switch to the North sector frequency (118.375 MHz), but the pilot did not acknowledge this instruction. Consequently, the glider entered the controlled airspace at FL 186 without authorization, forcing air traffic controllers to coordinate other traffic to maintain separation.
The investigation
The ÚZPLN investigation examined the pilot's flight planning, the radio communications between the aircraft and ATC, and the performance of the aircraft's equipment. The investigation also reviewed the distribution of flight plans by the Prague Flight Service (ARO) and the procedures followed by the air traffic controllers in the Southeast and North sectors.
Findings
- The pilot incorrectly filled out the flight plan, which led to the ACC not being informed of the intended flight altitude.
- The pilot failed to verify that his flight plan was active and entered Class C airspace without a clearance.
- The pilot used the Czech language for communications in a sector where English is the standard.
- The aircraft was equipped with an unapproved SSR transponder (Trimble TRT 250D) that had been installed by the pilot rather than an authorized technician. The transponder functioned inconsistently, providing Mode C altitude information only sporadically.
- The air traffic controller (EC) in the Southeast sector responded in English to a Czech-language call, which hindered effective communication.
- The controller did not confirm the pilot's receipt of the instruction to change frequencies.
- A flight service error resulted in the flight plan being sent to the wrong office, meaning the North sector controller also lacked the necessary flight information.