What happened
On 21 August 2004, a Pegasus Quik microlight, registration G-STYX, departed Rochester Airfield for a trial flight accompanied by an instructor and a passenger. While cruising at approximately 500 feet along the north coast of the Isle of Sheppey, the aircraft suddenly pitched up into a near-vertical position. This movement initiated a violent series of tumbling manoeuvres at speeds of roughly 100 mph.
During this sequence, the structural integrity of the aircraft failed. The trike unit, which housed both occupants, separated from the wing assembly following the failure of the monopole and front strut. The aircraft descended vertically, and the impact resulted in two fatalities.
The investigation
The AAIB examined the wreckage and the aircraft's maintenance history, focusing on the structural components of the 'A' frame uprights. Investigators discovered that the aircraft's upright upper fittings had previously undergone modifications intended to comply with Service Bulletin 116. This bulletin required the installation of additional rivets to strengthen the structure.
Technical analysis revealed that the modification on G-STYX was performed incorrectly. The additional rivets were not placed according to the manufacturer's instructions, and some of the hardware used did not meet the required specifications. Furthermore, the investigation found that the aircraft had not been maintained according to the recommended schedule, meaning a scheduled 100-hour inspection—which might have identified the faulty rivets—had been missed.
Findings
- The primary cause of the accident was the failure of the right upper fitting of the uprights.
- This failure caused the trim cable to tighten, increasing wing reflex and forcing the aircraft into an unrecoverable pitch-up and tumble.
- The incorrect installation of rivets during the implementation of Service Bulletin 116 directly led to the structural failure.
- The BMAA inspector responsible for the modification did not follow the Service Bulletin and lacked the necessary engineering experience and understanding of the component's construction.
- There was a lack of independent duplicate inspections following the structural modification.
Safety action
Following the accident, several safety recommendations were issued, including:
- A requirement for the CAA to issue a Mandatory Permit Directive to ensure Service Bulletin 116 is correctly applied to all similar aircraft.
- Recommendations for the BMAA to review its standards for the selection, training, and revalidation of inspectors.
- A call for the CAA to review policies regarding the use of helmets and shoulder harnesses in microlight aircraft.
- A recommendation that owners replace modified uprights with factory-modified components to ensure structural integrity.