Incident Description
Following landing, a Viscount aircraft was taxiing along the runway when a loss of hydraulic system pressure occurred. This rendered the wheel brakes and nosewheel steering inoperative. The aircraft subsequently departed the runway and rolled down a downslope area. The pilot attempted to raise the landing gear but the effort failed due to the hydraulic pressure loss. The aircraft continued its path and came to rest against the control tower.
Investigation Findings
Investigation into the incident revealed a fractured pipe line within the hydraulic system. Additionally, a non-return valve, which was designed to conserve pressure in the event of a pressure loss in the main hydraulic system, was found to be operating faultily. These findings were consistent with the hydraulic system pressure loss experienced during the taxi.