What happened
On July 12, 2020, a Cessna 172S, registration OK-KOD, was taxiing for departure at Prague/Ruzyně Airport (LKPR) when a fire broke out in the right main landing gear assembly. The aircraft was performing a sightseeing flight with a pilot and two passengers.
During taxiing from the South apron toward the intersection of taxiway E and runway 06, the pilot noted a rightward drift, which was attributed to a northern wind. To compensate, the pilot applied braking to the left wheel. During this process, the aircraft experienced a sudden loss of braking effectiveness and began to veer left, eventually coming to a stop on the boundary between the paved taxiway and the grass.
Shortly after stopping, the passengers noticed flames emerging from beneath the right landing gear aerodynamic fairing. The pilot attempted to use an onboard fire extinguisher, but the fire intensified. The pilot and passengers evacuated the aircraft, and the fire was subsequently extinguished by airport fire services using Panther fire tenders.
The investigation
The ÚZPLN investigation examined the aircraft's maintenance records, the pilot's actions, and the mechanical state of the braking system. Investigators found that the parking brake had not been fully released. A functional test of the parking brake mechanism revealed that the control rod's positioning pin did not fully engage the notch in the linkage guide under the instrument panel, leaving the brake partially applied.
Furthermore, the investigation reviewed the pilot's pre-flight procedures and communication with Air Traffic Control (ATC). It was noted that the pilot did not perform the required passenger briefing regarding emergency procedures and failed to verify the exact position of the parking brake lever as prescribed in the aircraft's operating manual.
Findings
- The primary cause of the incident was the pilot's failure to properly execute pre-flight tasks, specifically failing to ensure the parking brake was fully released.
- The partially applied parking brake, combined with the pilot's use of the left wheel brake to correct directional drift, caused excessive heat buildup in the braking system during an unusually long taxi of approximately 5 km.
- The overheating caused hydraulic fluid (Aeroshell Fluid 41) to leak from the brake cylinders and subsequent damaged tubing, which ignited upon contact with the hot surfaces.
- The pilot's actions during the emergency, including an attempt to return to the terminal while the aircraft was on fire and an uncoordinated evacuation, hindered the safety of the passengers.
- The pilot failed to notify ATC that the aircraft had crossed the runway 06 holding point due to the braking malfunction, thereby infringing on the runway protection zone.