What happened
On 29 May 2007, a modified Rans S6-ESD XL, registration G-MZDA, was conducting a private flight from Carlisle Airport, Cumbria. Shortly after departing from Runway 25, the aircraft was climbing at a rate of approximately 500 feet per minute. While at an altitude between 400 and 500 feet, the propeller, hub, spinner, and shaft became detached from the engine. This failure caused the engine speed to increase rapidly.
Following the detachment, the pilot lowered the aircraft's nose, maintained a speed of 60 mph, and executed a 180-degree turn to the right toward Runway 07. The pilot issued a 'mayday' call and, after receiving confirmation from the controller that the runway was clear, successfully landed the aircraft. There were no injuries to the pilot or the passenger, though the propeller and hub fell into a nearby field.
The investigation
Investigators examined the engine's reduction gearbox, specifically focusing on the mechanism intended to retain the propeller shaft. The shaft is held in place by two half-rings situated within an annular groove of a collar. While the engine had completed 600 hours, the gearbox had only 27 hours of operation since its most recent overhaul.
A metallurgical examination of the failed components revealed high cycle fatigue fractures within both the half-rings and the collar. Notably, there was no evidence of wear on the half-rings, and the components had been recently replaced during the gearbox overhaul. The broken collar had split into two pieces, and each half-ring had also fractured into two pieces.
Findings
- The primary cause of the incident was the fatigue failure of the annular collar and the half-rings within the reduction gearbox.
- The propeller, hub, spinner, and shaft became completely detached from the engine during the climb.
- The failure occurred despite the half-rings being recently replaced during a gearbox overhaul performed only 27 hours prior to the accident.