What happened
On March 16, 2008, a Cessna 152, registration OK-LEV, was conducting a navigation training flight for a student pilot. The flight, operated by Flying Academy s.r.o., followed a route through several Czech airfields, including LKLT, LKRO, and LKKB. During the flight, the crew encountered strong crosswinds that caused the student pilot to drift significantly off course toward Karlštejn.
While navigating, air traffic controllers at Kbely (LKKB) requested the pilot to verify the aircraft's Mode C functionality, as radar indicated the aircraft was only transmitting in Mode A. Despite the pilot's confirmation that Mode C was active, radar records and controller observations showed that the transponder was not functioning correctly throughout much of the flight. Between 13:04 and 13:06 UTC, the aircraft was identified as an unidentified target at FL065, despite the crew's intention to maintain a much lower altitude.
The investigation
The ÚZPLN investigation examined radar records from LKKB and radio communications to track the transponder's performance. The analysis revealed that the SSR transponder was only transmitting in Mode C during three specific intervals of the flight, during which the aircraft was recorded at FL067. For the remainder of the flight, the device operated only in Mode A.
Following the incident, the operator had the SSR transponder inspected by a specialized service company. The inspection found that while the device itself was not defective, the contact pins on the connection connector were damaged.
Findings
- The primary cause of the incident was damaged contact pins on the transponder's connection connector, which led to the intermittent failure of Mode C functionality.
- The aircraft's altitude deviation was detected by secondary radar due to this technical malfunction.
- The meteorological conditions, including wind, contributed to the pilot's initial course deviation but were not the cause of the transponder failure.