What happened
On September 18, 1997, at approximately 09:40, a stolen Robinson R22-B helicopter, registration OO-LJR, entered the airspace above the De Geerhorst penitentiary in Sittard, Netherlands. The aircraft had been stolen from Halen airport in Belgium and transported to the site via truck.
As the helicopter approached the prison courtyard, where inmates were being exercised, the pilot flew at a very low altitude. During the flight, the pilot dropped a handgun from the cockpit onto the courtyard. While attempting to maneuver the aircraft within the confined space of the prison yard, the helicopter's tail boom struck a 10-meter-tall light mast. This impact caused the aircraft to become unstable, leading to a catastrophic mechanical failure. The helicopter rolled onto its side and struck the ground, immediately catching fire. The pilot was killed in the crash, while one inmate sustained minor injuries.
The investigation
The investigation conducted by the Dutch Safety Board examined the aircraft's condition, the pilot's credentials, and the sequence of mechanical failures. Investigators determined that the Robinson R22-B was well-maintained and airworthy prior to the incident. However, the investigation revealed that the pilot was unlicensed and possessed extremely limited flying experience, likely consisting of only about 10 hours of instructional flight time.
Technical analysis of the wreckage showed that the horizontal stabilizer had been deformed by the collision with the light mast. Crucially, the investigation established that the impact and the pilot's subsequent aggressive control inputs triggered a phenomenon known as mast bumping. This caused the rotor blades to strike the mast, resulting in the breakage of one blade and the subsequent separation of the rotor mast from the gearbox.
Findings
- The pilot lacked a valid pilot's license and had insufficient experience to safely operate the aircraft.
- The confined dimensions of the prison courtyard and the presence of the light mast significantly restricted maneuvering options.
- The pilot used excessive and abrupt control inputs while attempting to stabilize the aircraft.
- Mast bumping occurred following the collision with the light mast, leading to the structural failure of the rotor system.
- The aircraft's destruction and the subsequent fire made the crash unsurvivable for the pilot.