What happened
On September 19, 2021, a Piper PA-42 aircraft, registration PT-MFL, was performing an air ambulance mission from Barra Grande to Salvador, Brazil. The flight, operated by Piquiatuba Táxi Aéreo Ltda., carried two crew members and four passengers.
During the landing roll at Deputado Luís Eduardo Magalhães Airport (SBSV), the pilot applied reverse thrust and engaged both brakes. At that moment, the pilot experienced a loss of pressure in the left brake pedal. This caused the aircraft to yaw to the right, resulting in a runway excursion where the aircraft exited the side of the runway and came to a stop on the adjacent grass area. There were no injuries to the six occupants, and the aircraft sustained no damage.
The investigation
CENIPA investigators examined the aircraft's braking system and maintenance history. They discovered a hydraulic oil stain on the right side of the fuselage, originating from the brake system drain. Upon inspection, the hydraulic fluid level in the brake reservoir was found to be below the minimum required level.
Further examination of the brake reservoir cap revealed that the sealing elastomer was damaged and worn. Although the aircraft had undergone a maintenance inspection only seven days prior to the incident, the investigation found that the faulty seal allowed fluid to leak out. Additionally, while the crew reported that the aircraft had previously experienced low braking effectiveness, these issues had not been recorded in the aircraft's technical logbook.
Findings
- The primary cause of the excursion was the loss of braking effectiveness due to low hydraulic fluid levels.
- The fluid loss was caused by a leaking brake reservoir cap with a deteriorated sealing elastomer.
- Inadequate maintenance services failed to identify or rectify the worn seal during the recent inspection.
- The absence of recorded technical irregularities in the aircraft logbook prevented the timely identification of the ongoing braking issue.