What happened
On August 31, 2005, a Robin DR 400-180 tug aircraft, registered F-GCIG, was taxiing at Toulouse Blagnac airport. The pilot was departing from parking position G, intending to fly to Romorantin. While taxiing approximately 2,000 meters along taxiway P behind an Airbus A320, the occupants noticed a burning smell and smoke emanating from the underside of the wing. Air traffic control notified the crew that the landing gear was on fire and alerted emergency services.
The pilot managed to move the aircraft off the taxiway and successfully evacuated the three passengers on board. Although firefighters responded quickly, the fire had already spread across the entire wing. The aircraft sustained significant damage, including a destroyed wing and heavy fire damage to the fuselage.
The investigation
Investigators examined the wreckage and determined that a brake line connected to the left brake caliper had failed under hydraulic pressure. The inspection revealed that the brake disc showed signs of overheating that appeared to have occurred prior to the fire. While the caliper and piston assembly appeared to be functioning correctly, the central brake handle exhibited a "hard point" at the end of its travel.
Technical analysis of the components showed that the left brake hose dated back to 1988, while the right hose dated to 1990. The maintenance program required these hoses to be replaced every ten years.
Findings
- The investigation established that residual pressure in the braking system, potentially caused by the mechanical resistance in the brake handle, led to an increase in temperature within the brake disc and caliper assembly.
- This overheating caused the hydraulic fluid to heat up, creating overpressure within the brake line.
- The left brake hose, which had exceeded its ten-year service life, lacked the necessary mechanical integrity to withstand this pressure and subsequently ruptured.
- The escaping hydraulic fluid ignited upon contact with the overheated brake disc.
- During the evacuation, although the pilot turned off the magneto, battery, and alternator switches, the fuel mixture lever was left in the full-rich position and the fuel circuit remained open.