Near Mid-Air Collision at Grenchen Airport Highlights Risks of Uncontrolled Airspace

Casualties unknown • Grenchen Flugplatz (LSZG), SO, CH

A high-speed approach by a business jet and a light aircraft resulted in a dangerous separation of only 0.1 NM near Grenchen, Switzerland.

What happened

On May 1, 2018, at approximately 17:05 local time, a serious airprox occurred near Grenchen Airport (LSZG). An Embraer Phenom 3/300, registration HB-VYS, was conducting an IFR approach from the east, transitioning to VFR flight rules. At the same time, a Robin DR 400/140 B, registration HB-KLE, was performing a VFR approach for runway 06.

As the HB-VYS approached the runway on a direct track for runway 24, the crew was maintaining a high ground speed of approximately 235 knots. Simultaneously, the HB-KLE was on its base leg for runway 06. The crew of the HB-VYS initiated a go-around because the approach was not stabilized. During the climb, the HB-VYS climbed to approximately 500 feet above the HB-KLE, with the horizontal separation dropping to just 0.1 NM.

The investigation

The SUST investigation examined the transition of airspace operations at Grenchen. At the time of the incident, the airport had recently transitioned from an active Control Zone (CTR) to a Radio Mandatory Zone (RMZ), where air traffic control services were no longer provided, and pilots were responsible for their own separation via blind transmissions. The investigation also reviewed the pilot's actions, the airport's communication procedures, and the accuracy of various aeronautical publications used by pilots in the region.

Findings

  • The crew of the HB-VYS demonstrated low situational awareness by continuing an approach on runway 24 despite the active use of runway 06 and the presence of opposing traffic.
  • The high approach speed of the HB-VYS made effective airspace surveillance difficult for the crew.
  • The go-around by the HB-VYS was not announced on the radio frequency, leaving other pilots unaware of the sudden change in flight path.
  • The transition between ATC-controlled airspace and the RMZ creates significant confusion and risk, as evidenced by a series of similar incidents at the airport.
  • Existing aeronautical publications and instructions regarding the RMZ were found to be inconsistent, incomplete, or even contradictory, which can mislead pilots during critical phases of flight.

Probable cause

The near mid-air collision was caused by the high-speed approach of the business jet on a runway contrary to the active traffic flow, compounded by a lack of situational awareness and the inherent complexities and confusion arising from the transition to uncontrolled RMZ airspace operations.

Frequently asked questions

What happened in the 2018-05-01 EMBRAER S.A. EMB-505 accident near Grenchen Flugplatz (LSZG), SO, CH?

A high-speed approach by a business jet and a light aircraft resulted in a dangerous separation of only 0.1 NM near Grenchen, Switzerland.

What aircraft was involved and where did it happen?

The accident on 2018-05-01 involved a EMBRAER S.A. EMB-505, registration HB-VYS, at Grenchen Flugplatz (LSZG), SO, CH.

What was the probable cause of the accident?

The near mid-air collision was caused by the high-speed approach of the business jet on a runway contrary to the active traffic flow, compounded by a lack of situational awareness and the inherent complexities and confusion arising from the transition to uncontrolled RMZ airspace operations.

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