What happened
On August 31, 2010, a serious airprox incident occurred near the SOSAL waypoint, approximately 17 km north of Montreux. The conflict involved a Hawker 4000, registered M-KENF, operating under Instrument Flight Rules (IFR), and a Mirage III DS, registered HB-RDF, operating under Visual Flight Rules (VFR).
The Hawker 4000 was conducting a private ferry flight from Geneva to Zurich, maintaining flight level 160. Simultaneously, the Mirage III DS, flying under the callsign EMIR 12, was performing a proficiency check and heading toward Payerne Air Base for an emergency landing practice.
During the climb, the pilot of the Mirage III DS utilized a high-performance military climbing technique. While authorized to climb to flight level 150, the aircraft's rate of climb reached approximately 10,500 feet per minute. This rapid ascent caused the aircraft to overshoot its assigned altitude, eventually reaching flight level 200. This maneuver led to a convergence with the Hawker 4000, resulting in a loss of separation for 41 seconds. At the closest point, the vertical separation was reduced to only 200 feet.
The investigation
Investigators analyzed radar tracks, radio communications between the two different air traffic control sectors (civil and military), and pilot statements. The investigation established that the aircraft were being managed by two separate controllers in different sectors.
While the civil sector's Short Term Conflict Alert (STCA) triggered a proximity warning, the military sector's radar did not receive an alert. The investigation found that the Hawker 4000 was equipped with TCAS, whereas the Mirage III DS was not. The pilot of the Mirage III DS admitted to being momentarily distracted and confirmed that the high rate of climb was intentional to reach the assigned level quickly, which ultimately led to the altitude excursion.
Findings
- The pilot of the VFR flight employed an excessive rate of climb characteristic of military flight profiles.
- The Mirage III DS exceeded its authorized flight level of FL 150.
- The aircraft trajectories converged at a right angle, creating a high-risk situation.
- There is a lack of standardized climb/descent rate limitations for VFR aircraft operating within controlled airspace, unlike the established procedures for IFR traffic.
Safety action
To address the safety deficit, the investigation resulted in a safety recommendation (no. 442) suggesting that the Federal Office of Civil Aviation should require all aircraft operating in controlled airspace to adhere to the same procedures regarding climb and descent rate limits during altitude changes.