What happened
On July 21, 2000, at 17:15 UTC, an air traffic incident occurred in the Zurich TMA, east of EKRIT. A Swissair flight, SWR 693, operating an Airbus A321 (HB-IOK) from Lisbon to Zurich, was flying under IFR at flight level 60. While following a prescribed track, the crew spotted the silhouette of a light aircraft approximately 500 meters ahead on a similar heading and altitude.
The crew of the Airbus A321 performed a small dive of approximately 300 feet to pass beneath the unidentified aircraft to maintain visual contact and identify the type and registration. During this maneuver, the crew estimated the minimum lateral separation at 0.1 NM and a vertical separation of 0 FT before the descent. The aircraft was identified as a Mooney (MO-20), registration HB-DET, which was operating a VFR flight from Birrfeld.
The investigation
The investigation established that the Mooney was flying a route toward the Black Forest, following a GPS waypoint. While the pilot was aware of the altitude restrictions within the various TMA sectors—specifically that flight levels above 5500 FT in TMA Sector 4 required ATC authorization—the aircraft exceeded this limit without notification.
Radar analysis confirmed that the HB-DET appeared on primary radar without correlation (lacking identification or altitude data) for approximately 24 seconds, coinciding with the encounter with SWR 693. The investigation found that the pilot of the Mooney had left the transponder in the standby position. Although the pilot had conducted a weather briefing and consulted NOTAMs, no communication was established with the Zurich arrival controller during the unauthorized transit of the controlled airspace.
Findings
- Both aircraft were operating within Class C controlled airspace.
- The Swissair flight was under continuous radar contact and IFR procedures.
- The pilot of the Moont was flying under VFR and had not contacted any air traffic services after departing Birrfeld.
- The Mooney exceeded the permitted altitude in TMA Sector 4 without obtaining the necessary clearance.
- The pilot failed to contact the responsible air traffic control unit, preventing controllers from providing separation instructions.
- The transponder on the HB-DET was set to standby, rendering the aircraft invisible to secondary radar identification.
Safety action
To prevent similar occurrences, a safety recommendation was issued to amend the VFR-guide RAC 1-4. The amendment mandates that for all VFR flights within Class E airspace, the transponder must be set to code 7000, Mode A/C.