What happened
On 17 May 2014, a CZAW Sportcruiser, registration G-MELL, was performing an air test to evaluate its handling at the Never Exceed speed (VNE). The flight originated from Chilsfold Farm, West Sussex, with the intention of completing the test near Westcott, Hertfordshire, before returning to Elstree.
During the final phase of the test, the pilot initiated a dive from 3,000 ft to reach the VNE of 138 kt. While descending at approximately 125 kt and 1,700 ft, a loud bang occurred, followed by violent oscillations in pitch. The aircraft's canopy fractured, and the sudden forces caused a fire extinguisher to dislodge from its stowage, striking the pilot's leg. The pilot also experienced significant negative 'g' forces, which caused his headset to be pulled from his head and strike the broken canopy.
After managing to stabilize the aircraft at a lower speed, the pilot opted to continue to Elstree rather than perform an emergency landing in a field. However, as the aircraft accelerated to 77 kt, the broken canopy pieces began to flap, causing the pitch oscillations to return. The pilot maintained a speed of 70 kt for the remainder of the flight. Upon landing, a post-flight inspection revealed that the tailplane had suffered severe buckling on both sides, nearly reaching a state of complete structural failure, with accompanying damage to the elevator and flaps.
The investigation
The AAIB investigation examined the structural integrity of the aircraft and the sequence of events leading to the instability. Investigators considered whether a birdstrike had caused the initial canopy rupture, but no evidence of organic remains was found.
Analysis of the cockpit environment and the pilot's injuries suggested that significant negative 'g' loads were present. Testing overseen by the Light Aircraft Association (LAA) confirmed that even with a seat harness fastened, there was enough movement within the cockpit to allow the pilot's head to strike the canopy and for the fire extinguisher to exit its stowage.
Findings
- The primary cause of the structural damage was likely a sharp vertical gust of wind that overstressed the tailplane.
- This aerodynamic event created a 'g' spike that simultaneously caused the canopy to fracture and the unsecured fire extinguisher to become unrestrained.
- The pilot's head struck the canopy due to the vertical forces experienced during the oscillation.
Safety action
Following the incident, the LAA issued an Airworthiness Information Leaflet to all Sportcruiser owners, which reduced the VNE from 138 kt to 120 kt as a temporary measure. An Airworthiness Alert was also released to highlight the risks associated with unsecured cockpit equipment. The LAA has since initiated a structural review of the tailplane design to evaluate the possibility of lifting the speed restriction.