GPS Interference Incident Involving a Cessna Citation CJ3+ in Cyprus FIR (SP-CUD)

Incident Overview and Investigation Details On April 29, 2019, a Cessna Citation CJ3+ (C525B) was involved in an incident classified by the Polish State Commission for Aviation Accident Investigation (PAŃSTWOWA KOMISJA BADANIA WYPADKÓW LOTNICZYCH) as an aviation incident. The event occurred within the Cyprus FIR, specifically the Nicosia sector. The investigation, supervised by Jerzy Girgiel, was concluded on June 4, 2019. No fatalities, serious injuries, or minor injuries were reported among the crew, who consisted of a pilot holding an ATPL(A) license. ## Operational Sequence and Technical Failures The incident was part of a series of GPS-related issues reported by the crew during three consecutive flights. On April 27, 2019, during a flight from Poznań (EPPO) to Larnaca (LCLK), the crew observed fluctuations in the GPS synthetic vision system and several GPS switches. The system briefly entered dead reckoning (DR) mode, though the final approach to Runway 04 was completed without further disruption. On April 29, 2019, during a flight from Larnaca (LCLK) to Linz (LOWL), the crew lost indications from both GPS units. This resulted in the emission of synthetic vision, terrain fail, and ADS-B fail signals. The condition persisted for approximately 10 minutes while the aircraft was at approximately Flight Level 400. Later that same day, during the return flight from Linz (LOWL) to Larnaca (LCLK), the crew experienced further GPS fluctuations. After passing the LCA VOR, the GPS indications were lost and the system transitioned to DR mode. An instrument landing was performed. During the turn to the landing course, the GPS signal returned, causing the Garmin map to shift by approximately 2 to 3 nautical miles. The interference ceased on the final approach. ## Probable Cause and Safety Measures The investigation determined that the cause of the events was military actions conducted in the area of the aircraft's flight path, which resulted in external interference with the GPS signal. The operator noted that GPS signal loss in aircraft equipped with G1000/G3000 avionics represents a real threat to flight operations. Following the incident, the operator informed pilots and collected additional information from crews regarding GPS interference. A new Information Notice was issued regarding operational restrictions in certain countries or areas. Additionally, the manufacturers Cessna, Honda, and Garmin were informed of the incident and requested to provide their views on the situation. The operator also issued safety recommendations for crews operating near conflict zones, including the use of alternative navigation means, maintaining two-way radio communication with ATC, and monitoring frequency 121.500 MHz.