What happened
On April 30, 2009, a paramotor, registration PH-9E9, was conducting a local flight along the coast near Scheveningen, Netherlands. While flying at an altitude of approximately 150 meters, the pilot was approached by a police helicopter, registration PH-RPZ, which was performing a flight to check the altitude of the two paramotors present. The helicopter crew intended to identify the aircraft to issue a citation for a potential altitude violation.
During the encounter, the wing of the PH-9E9 partially collapsed. The pilot managed to recover the wing, but the sudden change in vertical speed caused the propeller blades to strike the protective cage, resulting in significant damage to the propeller and the cage netting. The pilot was forced to perform an emergency landing on the beach. No injuries were reported, though the aircraft was rendered unairworthy.
The investigation
The investigation focused on the interaction between the helicopter and the paramotor. While the helicopter crew maintained they approached at a safe distance of 50 to 60 meters and did not observe any abnormal flight behavior, the pilot of the PH-9E9 and a second nearby paramotor reported feeling significant turbulence and shaking caused by the helicopter's proximity.
Investigators examined the meteorological conditions, noting that the wind was light and there was an absence of natural turbulence. This lack of ambient wind meant that the vortices and downwash generated by the helicopter's rotors did not dissipate quickly, potentially lingering in the flight path of the paramotor.
Findings
- The primary cause of the wing collapse was turbulence generated by the helicopter.
- The lack of natural wind and existing turbulence contributed to the persistence of the helicopter's rotor wash.
- The physical damage to the PH-9E9 was caused by the abrupt deceleration of the aircraft when the wing re-inflated after the partial collapse.
- The risks associated with helicopter approaches are not uniform across all aircraft types; aircraft with non-rigid wing structures, such as paramotors, are particularly vulnerable to loss of lift from rotor wash.
Safety action
At the time of the incident, the Dutch Police Aviation Service lacked specific, written procedures for the interception and identification of aircraft. While a new operational procedure was being drafted, investigators noted that the draft version still lacked specific safety criteria or minimum separation distances tailored to different categories of aircraft, particularly those sensitive to airflow disturbances.