What happened
On May 16, 2023, an AT-502B aircraft, registration PS-CGF, was performing a local crop-dusting flight at the Ceolin Grãos e Fibra Aerodrome in São Desidério, Bahia. The aircraft touched down approximately 200 meters beyond the threshold of runway 26. During the landing roll, the pilot experienced a sudden loss of directional control, causing the aircraft to veer toward the left-hand side of the airstrip.
The pilot attempted to use the rudder pedals and subsequently applied the right-hand brake to regain control, but the action was ineffective. The aircraft eventually exited the runway limits and collided with a perimeter barbed-wire fence, which caused the aircraft to rotate abruptly to the left before coming to a stop. The aircraft sustained minor damage to the fuselage, wings, and propeller blades, but the pilot escaped without injury.
The investigation
CENIPA investigators examined the aircraft's braking system, including the brake pads, discs, and hydraulic fluid levels. While the fluid reservoir was found to be adequately supplied, investigators noted that the right-hand brake pedal exhibited a "soft" behavior with long travel and little initial resistance. This condition matched the pilot's report that the pedal sank without providing effective braking.
The investigation focused on why the right-hand brake lost its effectiveness. While the aircraft's maintenance logs were up to date, the committee considered whether air had entered the hydraulic system. Two hypotheses were explored: an inadequacy during a brake pad replacement performed approximately one year prior, or an unlogged maintenance intervention occurring after that inspection that introduced air into the lines.
Findings
- The runway excursion was caused by the loss of effectiveness of the right-hand brake assembly.
- The loss of braking performance was likely due to air entering the hydraulic system.
- The pilot was fully qualified and experienced for the type of operation.
- Meteorological conditions were favorable and well above flight minimums.
- The aircraft was within weight and balance limits and had a valid airworthiness certificate.