What happened
On September 12, 1999, a Boeing 737-300 operating as KLM 1933 was on an intermediate approach to Geneva Airport. While descending through 7,000 feet under radar guidance from Geneva Arrival control, the pilot requested a turn toward the final approach for runway 05. At that moment, the air traffic controller identified an unidentified aircraft traveling in the opposite direction near the Chambéry VOR, flying at approximately 6,500 feet.
To maintain separation, the controller instructed KLM 19 and kept the aircraft at 7,000 feet while providing frequent traffic updates. Despite the clear visual meteorological conditions, the crew of the Boeing 737-300 could not visually locate the unknown traffic. The situation escalated when the aircraft's Traffic Collision Avoidance System (TCAS) issued a resolution advisory, prompting the pilot to climb to avoid a potential collision. During the encounter, the minimum separation between the two aircraft was recorded at 1.3 NM horizontally and 600 ft vertically.
The investigation
The investigation focused on the movement of the unidentified aircraft and the effectiveness of the separation provided by Geneva Arrival control. Radar analysis revealed that the unknown aircraft had entered the Geneva terminal control area (Class C airspace) from the Chambéry TMA (Class E airspace) without establishing radio contact or obtaining the necessary transit authorization. The aircraft was observed descending from 7,700 feet to 6,500 feet before entering the Geneva sector.
Investigators also examined the controller's actions, noting that the controller successfully maintained separation by holding KLM 1933 at a higher altitude than the intruder and even instructed another incoming flight, Speedbird 730, to limit its descent to avoid the hazard. The investigation noted that the unidentified aircraft's route involved traversing multiple airspace classes, suggesting that inaccurate navigation or chart reading may have caused the unauthorized incursion.
Findings
- The primary cause of the incident was an unauthorized incursion of an unidentified aircraft into the Geneva Class C terminal area.
- The unidentified aircraft failed to make radio contact with Geneva Arrival control, entering the sector without authorization.
- The pilot of KLM 1933 was unable to maintain visual contact with the intruder despite the presence of VFR conditions.
- The TCAS resolution advisory was necessary to maintain vertical separation as the aircraft's flight paths were projected to cross.