Introduction
On 9 June 2001 at 08:59 UTC, an Airprox (near collision) occurred on final approach to runway 14 at Bern airport, involving aircraft HB-LEU (a Piper PA34 operated by Gribair AG) and REGA 3 (an Agusta A109, registration HB-XWO, operated by Rega). The incident took place in controlled airspace class D under instrument meteorological conditions (IMC).
Sequence of Events
HB-LEU was conducting an instrument landing system (ILS) approach to runway 14. On board were a pilot responsible for the flight and a flight instructor acting as safety pilot. The flight was intended as a training exercise for an upcoming proficiency check. The crew discussed whether the applicable minimum altitude was the decision altitude (DA) of 1870 feet (as per Jeppesen manual) or the minimum descent altitude (MDA) of 2800 feet prescribed for training approaches in the Aeronautical Information Publication (AIP). They agreed that because the flight plan field 8 (Type of Flight) was marked with "G" for General Aviation, they were permitted to descend to 1870 feet.
Meanwhile, REGA 3 requested departure for a medical evacuation flight to Langenthal. At 08:58:20, the helicopter contacted Bern tower and was cleared for take-off along the runway axis, initially not exceeding 2000 feet. The safety pilot of HB-LEU heard the clearance and recognized a potential conflict because HB-LEU was still descending toward 1870 feet. Initially, he maintained visual contact with the helicopter, but when REGA 3 entered a cloud layer, visual contact was lost. He then ordered an immediate go-around at 08:59:35.
At 08:59:15, the controller asked HB-LEU if it was executing a go-around; the pilot replied "Not now, approaching minimum." A brief discussion ensued regarding the authority to descend below the MDA. The two aircraft passed each other with a lateral distance of 100–200 meters and a vertical separation of 20–30 meters.
Investigation Findings
The investigation found that both aircraft complied with all ATC clearances. The crew of HB-LEU firmly believed they were authorized to descend to the DA of 1870 feet, while the controller was convinced that HB-LEU would only descend to the MDA of 2800 feet. The controller based this assumption on recognizing the aircraft as belonging to a local flight school, primarily used for training.
The flight plan of HB-LEU had field 8 marked with "G," but this information was not visible on the control strips available to the controller. Field 18 (Other Information) contained "1 ILS APCH" in abbreviated form.
Weather at the time (METAR Bern 0850) reported: wind 160° at 2 knots, visibility 4000 meters, rain, clouds 1-2/8 at 300 feet, 3-4/8 at 1800 feet, 5-7/8 at 3500 feet, temperature 12°C, dew point 12°C, QNH 1012 hPa.
Probable Cause
The incident occurred because the crew of HB-LEU continued their approach to the decision altitude of 1870 feet following non-compliance with the regulations governing a training flight. Contributing factors were a lack of clarity in the formulation of the flight plan data and a lack of situational awareness by both the controller and the crew of HB-LEU.