What happened
On August 19, 2006, a Reims F152, registration PH-HGO, was conducting a VFR overland flight from Rotterdam Airport. After climbing to approximately 3,500 feet, the pilot descended to 1,400 feet AMSL while transiting toward the Soesterbog Airbase (EHSB) controlled airspace. Having received permission from Dutch Mil Info to cross the CTR via Utrecht, the pilot proceeded into the area.
Simultaneously, a Schleicher ASK 23B glider, registration PH-774, was performing a local flight at Soesterberg. Following a winch launch, the glider pilot had just reached an altitude of approximately 1,200 feet AAL and was preparing to disconnect from the cable. At that moment, the Reims F152 passed extremely close to the glider, flying horizontally across the winch cable path at a vertical separation of only about 15 to 30 meters below the glider. The glider pilot observed the engine aircraft passing just 30 to 50 meters ahead of them. There were no injuries and no damage to either aircraft.
The investigation
The investigation focused on the unauthorized entry into the airfield traffic zone (ATZ) and the lack of separation between the two aircraft. Investigators found that while the pilot of PH-HGO had requested permission to cross the CTR, they did not specify a height, and because the aircraft's altitude could not be determined via radar, the flight information service could not warn of the potential conflict.
Furthermore, the investigation examined the regulatory discrepancy between the ATZ boundaries and published winch cable heights. While the ATZ extends to 1,500 feet AAL, the Aeronautical Information Publication (AIP) for Soesterberg lists maximum winch cable heights of up to 2,000 feet AAL. This discrepancy creates a false sense of security for pilots flying above the ATZ limit but below the cable height.
Findings
- The primary cause of the incident was the unauthorized entry of PH-HGO into the Soesterberg ATZ.
- The pilot of the Reims F152 failed to maintain safe flight operations by flying directly over an active winch-launch area, despite the known presence of glider operations at the base during weekends.
- A significant safety risk exists due to the mismatch between the vertical limits of the ATZ (1,500 feet AAL) and the published maximum winch cable height (2,000 feet AAL).
Safety action
The Dutch Safety Board recommended that the Human Environment and Transport Inspectorate (IVW) revise the vertical dimensions of ATZs for controlled military airfields. The goal of this revision is to ensure a safe margin between the edge of the traffic zone and the maximum published winch cable heights.