What happened
On 15 January 2012, a Yak-52, registration G-LYFA, was being prepared for a private flight at Manchester Barton Airfield. The aircraft had been parked on a grass area for approximately eight weeks following a period of inactivity. After completing an engine warm-up, the pilot increased power to begin taxiing along the hard surface of the taxiway.
As the pilot attempted to initiate a turn using left rudder and brake application, the aircraft failed to respond to the controls. The aircraft continued to roll forward across the taxiway surface without any braking effect. This uncontrolled movement resulted in a low-speed collision with an airfield building located on the opposite side of the taxiway. The impact caused damage to the aircraft's propeller and engine cowling, while the building sustained minor damage, including a broken window sill and scoring from the propeller.
Following the incident, the two crew members ensured the engine was shut down correctly and vacated the aircraft. The aircraft was subsequently moved back to its original parking position.
The investigation
Investigators examined the aircraft's systems to determine why the braking mechanism failed during the taxi. An inspection conducted by the aircraft's maintenance organisation identified leaks in the pneumatic system's undercarriage 'down' line. Because this specific line provides the necessary pressure for the pneumatically operated brake units, the loss of pressure directly prevented the pilot from slowing or steering the aircraft.