What happened
On June 9, 2001, a Piper PA34, registration HB-LEU, was performing an ILS approach to runway 14 at Bern Airport. The flight was being conducted for training purposes, with a flight instructor acting as a safety pilot to observe the pilot-in-command during a proficiency check. The flight was operating under Instrument Meteorological Conditions (IMC).
Simultably, a REGA Agusta A109 helicopter, registration HB-XWO, requested departure from the Bern tower to transport a patient to Bern University Hospital. The air traffic controller cleared the helicopter to depart along the runway axis with a maximum altitude of 2,000 feet.
As the Piper PA34 continued its descent, the safety pilot noticed the approaching helicopter. While the crew initially maintained visual contact, the helicopter soon descended below the cloud base, breaking visual contact. To avoid a collision, the safety pilot ordered an immediate go-around. The two aircraft eventually passed each other with a lateral separation of approximately 100–200 meters and a vertical separation of only 20–30 meters.
The investigation
The SUST investigation focused on why the aircraft were on conflicting paths. The investigation established that the Piper PA34 crew believed they were authorized to descend to a Decision Altitude (DA) of 1,870 feet. However, because the flight was a training flight, Swiss AIP regulations required a Minimum Descent Altitude (MDA) of 2,800 feet to mitigate noise.
The controller believed the aircraft was adhering to the 2,800-foot MDA. This misunderstanding was exacerbated by technical limitations in the flight plan data display at the tower, which did not clearly show the flight's specific category, making it difficult for the controller to identify the flight as a training mission.
Findings
- The primary cause was the crew of HB-LEU descending to 1,870 feet in violation of the requirements for a training flight.
- Inadequate flight plan data visibility prevented the controller from seeing the specific flight category in the control strips.
- A lack of situational awareness contributed to the incident, specifically from both the controller and the aircraft crew.
- The controller's separation plan relied on the assumption that the aircraft would maintain the higher MDA of 2,800 feet.