What happened
During a local training flight at Cork Airport, a Piper PA 34-200T Seneca II, registration EI-CMT, experienced a significant runway excursion on Runway 25. While on final approach, the low evening sun obscured the pilots' forward visibility, making it difficult to judge the landing flare. As a result, the aircraft floated and touched down approximately 476 metres beyond the standard touchdown point.
Upon landing, the instructor noticed inadequate braking performance. As the instructor attempted to use the brakes, the left pedal felt unresponsive while the right pedal caused the right main wheel to lock and skid, creating asymmetric braking that made directional control difficult. As the aircraft continued down the runway, the student pilot applied heavy braking. This action caused both main wheels to lock up, leading the tyres to wear through and deflate. With the loss of effective braking, the aircraft departed the paved surface at roughly 40 knots, traveling 30 metres into the grass. The two crew members on board were uninjured.
The investigation
An investigation by the AAIU examined the aircraft's braking system and the circumstances of the landing. Technical inspections of the brake assemblies revealed that the brake bleed fittings on both main wheels had been damaged when they contacted the pavement following the tyre deflation. The left brake assembly required a new caliper unit because the bleed seat had been sheared.
Further examination of the brake master cylinders and seals showed they were in good condition and had been properly maintained. However, the investigation determined that air had entered the hydraulic lines between the master cylinder and the wheel assemblies. This air made the hydraulic fluid compressible, which significantly reduced the effectiveness of the brakes.
Findings
- The low position of the sun during the evening approach hindered the pilots' ability to see the runway clearly, leading to a deep touchdown.
- Air in the braking system caused asymmetric braking performance and reduced deceleration capability.
- The application of heavy braking by the student pilot caused the main wheels to lock, which directly led to the deflation of the tyres and the subsequent loss of all remaining braking force.