What happened
On 4 November 2022, a Saab 340B operated by Pel-Air Aviation Pty Limited was taxiing for runway 32 at Flinders Island Airport. During the initial stages of the take-off roll, the aircraft veered toward the left, and the crew noted that acceleration was not meeting expectations. The pilot subsequently decided to reject the take-off.
Following the incident, an inspection revealed that all main landing gear tyres were deflated and one tyre exhibited a flat spot. Runway evidence showed significant tyre marks from all four main wheels, which began early in the roll and continued until the aircraft came to a stop. The change in the pattern of these marks—from solid lines to parallel lines—indicated that the weight of the aircraft was being supported by the wheel rims, confirming the tyres had deflated during the roll.
The investigation
The investigation focused on why the brakes were dragging and why the tyres deflated. Analysis of the flight data recorder and engine parameters confirmed the issue was related to the braking system rather than propulsion. The investigation found that the heat generated by the dragging brakes caused the fusible plugs in the wheel assemblies to melt, leading to the loss of tyre pressure.
Evidence suggested that the parking brake handle was likely not completely seated in the console. This improper positioning caused the common hydraulic return line for both the inboard and outboard circuits to be partially obstructed. This obstruction prevented hydraulic fluid from flowing out of the system efficiently, meaning pressure was not fully relieved when the brake was released.
Findings
- The primary cause of the brake dragging was the incomplete resetting of the parking brake handle, which left residual pressure in the hydraulic system.
- This residual pressure caused the brakes to remain partially applied during taxi, generating significant friction and heat.
- As the aircraft accelerated during the take-off roll, the heat increased rapidly, eventually causing the fusible plugs to activate and the tyres to deflate.
- The pilot's taxi speed was noted to be slower than usual to allow cabin preparation, which may have masked the presence of the dragging brakes.