What happened
On 21 July 2012, a Piper PA-28-161 aircraft, registration G-TLET, was conducting circuit training near Shoreham Airport. During the climb-out phase of the third 'touch-and-go' maneuver, at an altitude of approximately 200 feet, the aircraft experienced a sudden and significant loss of engine power. The instructor pilot immediately initiated a forced landing procedure, declaring a MAYDAY.
The aircraft descended into a field south of the runway and the nearby railway track. During the landing sequence, the aircraft struck a fence, a hedge, and a large mound of earth. The impact with the mound caused the landing gear to collapse and the wheels to separate from the airframe. Despite the significant damage to the propeller, landing gear, and wing spar, the crew of two escaped the aircraft without injury.
The investigation
Investigators examined the engine's Full Authority Digital Engine Control (FADEC) data, which confirmed that manifold pressure dropped by 50% shortly after takeoff, while the throttle remained at 100% position. The investigation focused on a failed Wiggins clamp located between the turbocharger compressor outlet and the turbo pipe assembly.
Metallurgical analysis of the failed clamp revealed that the fracture originated from multiple sites on the inner diameter and propagated through the sidewall. Significant fretting wear was observed on the inner surface, suggesting that engine vibrations or potential pipe misalignment contributed to the fatigue. Further investigation of the maintenance history showed that the clamp had been in service for a period that potentially exceeded the recommended replacement interval, and the maintenance organization was unaware of the specific 300-hour removal and inspection requirement.
Findings
- The loss of power was caused by the failure of a clamp between the turbocharger compressor outlet and the turbo pipe assembly.
- The failure was due to a fatigue crack that initiated at multiple points on the inner surface of the clamp.
- Significant fretting wear on the inner surface indicated that engine vibrations likely contributed to the crack initiation.
- Inconsistent maintenance requirements across different aircraft types meant that the necessity for clamp removal and inspection was not universally applied.
Safety action
- Technify Motors GmbH is recommended to inform operators of aircraft fitted with these engines that the Wiggins clamp is susceptible to cracking.
- The engine manufacturer should establish a consistent inspection and replacement interval across all relevant maintenance manuals.
- The manufacturer should re-evaluate the vibration and loading conditions of the clamp to determine if an alternative design is required to prevent future failures.