Accident Sequence
On 29 June 1994, a Cessna Citation II C-550, registration HB-VIS, operated by Cat Aviation AG, was involved in an accident during landing at Zurich Airport, Runway 14. The flight crew consisted of a female pilot-in-command (born 1950) and a male copilot (born 1967), with two passengers. The previous day, the pilot had noticed a tendency for the aircraft to veer right during taxi and required more power than usual. The parking brake was inspected by the maintenance company, Jet Aviation Zurich, but no defects were found.
On the day of the accident, during the return flight from Bologna, the copilot was at the controls. While leaving the parking position, he noted that the aircraft barely moved at taxi power. The PIC then released the parking brake. During taxi to the runway, a slight right veer was observed. Since no technical fault had been found the previous day, the PIC decided to proceed with the takeoff and performed it herself.
On landing at Zurich, the aircraft suddenly veered to the right. The PIC immediately took over the controls and applied left brake and rudder. Despite her actions, the aircraft departed the runway at low speed with the right brake locked and a flat tire. All occupants were uninjured. The landing gear and flaps were damaged, and runway lights were struck.
Investigation
The investigation revealed that the brake discs and linings of the right main wheel had welded together due to intense heat. This occurred because the valve that returns brake fluid from the hydraulic system did not open fully. A worn pushrod had caused elongation of the parking brake control cable travel, preventing the valve from opening completely. The parking brake valve had accumulated 3,396 hours and 3,940 landings. No periodic inspection of the valve travel was specified in the manufacturer's maintenance instructions.
Cause
The accident was attributed to wear of the parking brake valve, which led to overheating and blocking of the right main wheel, causing the aircraft to veer to the right during landing.