What happened
On 18 August 2018, a CZAW Sportcruiser, registration G-CGJS, was conducting a private training flight near Clacton-on-Sea, Essex. The flight, which involved the pilot/owner and a class rating instructor, was intended to practice crosswind landings. After taking off from Clacton Airfield, the aircraft was climbing through 1,400 ft when a loud noise was heard from the engine, followed by a total loss of power.
As the engine failed, the instructor took over radio communications with Southend Radar while the pilot focused on the aircraft. Unable to return to the airfield, the pilot identified a suitable field for an emergency landing. Although the chosen field was deeply furrowed due to a potato crop, the pilot successfully executed a forced landing. Upon touchdown, the aircraft's nose wheel detached due to the impact, causing the aircraft to slide to a halt. There were no injuries to the two occupants.
The investigation
The AAIB examined the engine following the accident and discovered that the flywheel had detached. This separation was caused by the failure of the attachment bolts, with evidence of fatigue found on at least one bolt.
The investigation also focused on the maintenance history of the Jabiru 3300A engine. The aircraft was fitted with a Sensenich propeller, which the engine manufacturer classified as a "non-approved" propeller. This classification triggered specific maintenance requirements. The investigation revealed a significant discrepancy between different manufacturer documents regarding how often these bolts needed replacement. While the engine Maintenance Manual required replacement every 100 hours, a Service Bulletin available on the manufacturer's website suggested a 500-hour interval. The pilot had been following the 500-hour interval, and at the time of the accident, the bolts had been in use for 447 hours.
Findings
- The engine failure was caused by the fatigue failure of the flywheel attachment bolts.
- A conflict in manufacturer documentation led to the bolts being used beyond their intended 100-hour service life.
- The pilot had been adhering to a 500-hour replacement schedule found in a published Service Bulletin, which contradicted the engine's Maintenance Manual.
Safety action
Following the incident, the engine manufacturer issued Service Bulletin JSB 014-3 to align the maintenance requirements for non-approved propellers with the Maintenance Manual, ensuring a consistent 100-hour replacement interval. Additionally, the manufacturer introduced hardware improvements, such as Nordloc washers, to enhance the security of the flywheel attachment system.