Synopsis
On 19 October 1999 at 0600Z, a HS-125-400A aircraft registered ZS-OIF was parked in a hangar at Lanseria. The pilot arrived at approximately 0500Z and began the pre-flight inspection. A person from the maintenance organisation offered to pump the hydraulic system, but the pilot replied that it was not necessary and he would do it later. The aircraft was then towed to the international departures apron for refuelling. While the pilot continued the external pre-flight inspection, the co-pilot arrived. At approximately 0540Z, after completing the external inspection, the pilot boarded the aircraft to complete the cockpit pre-flight inspection.
Sequence of Events
The park brake was set, and the co-pilot proceeded to remove the chocks. Upon removal of the chocks, the aircraft started rolling forward. The co-pilot attempted to re-insert the chocks, but this had no effect as the aircraft rolled over them. The pilot initiated start-up of engine number two in an attempt to build hydraulic pressure. Unfortunately, there was not enough time, and the aircraft rolled into an adjacent hangar, causing extensive damage to the under-belly and wing skin.
Post-Accident Observations
On arrival at the scene, both accumulator gauges indicated approximately 1000 PSI. This implies zero hydraulic system pressure, since 1000 PSI pressure is maintained by nitrogen gas in the accumulators.
Probable Cause
The hydraulic system was not pressurised during the pre-flight inspection of the aircraft. The chocks were therefore removed without adequate hydraulic system pressure available.