We brought our failure analysis expertise to an investigation into a fatal gyroplane accident, informing national safety recommendations that will reduce the risk of similar accidents and help save lives.
The challenge: understanding why a gyroplane crashed
We were asked by the Air Accidents Investigation Branch (AAIB) to contribute to its investigation into a fatal accident. The accident involved a solo student pilot whose gyroplane crashed when its rotor head separated from the fuselage.
Applying nC2’s failure investigation expertise
Understanding the failure mechanism
The model of gyroplane that was involved in the accident
The investigation focused on two of the gyroplane’s rotor head components: the damaged aluminium gimbal block, and the deformed steel roll stop bar on the gyroplane’s mast.
For the gimbal block, we used fractography to understand the sequence of the fractures.
- Macroscale imaging determined the fracture order.
- Scanning electron microscopy showed ductile dimples and brittle cleavage of inclusions, confirming instantaneous overload rather than progressive failure.
The steel roll stop bar and associated side plates were examined as follows:
- A weld inspection showed that the welds holding the roll stop bar in place had failed. These were ‘tack welds’ rather than full strength welds, as in normal operation they were not expected to carry significant load.
- CT scans showed the distortion of the roll stop bar, shallow weld size and weld failure.
The evidence pointed to the roll stop bar making contact with the gimbal block in flight due to the dynamic flight loads caused by a sequence of manoeuvres. This caused the gimbal block to fracture and break apart, and resulted in the rotor and fuselage becoming detached. This type of contact was unanticipated as the gimbal block channel is only intended to act as a control stop when the gyroplane is on the ground, not in flight.
Testing the theory in the lab
The mechanical test rig
To confirm their hypothesis, the team set up a mechanical test rig in the lab to recreate the accident conditions using new components.
- Simulating the scenario involved designing a jig to hold the components and apply load to the gimbal block.
- A solid test rig was used with a 630kN loading capacity.
- Sensors were attached to the components to record local strain.
- Cameras were set up for a visual record of the test.
After the test, we analysed the components and compared them to the accident components. The damage on the test components closely matched that seen on the accident gimbal block and mast.
- The steel roll stop bar was bent in the same way.
- Similar indentations were found on the gimbal block.
- Cracks on the gimbal block formed in the same locations.
As stated in the AAIB’s final report, nC2’s testing and analysis “confirmed that the separation [of the rotor head and mast] was caused by a structural overload failure of the gimbal block from a single continuous exposure to dynamic flight loads”.
nC2’s added value
We brought to the investigation:
- Internationally recognised expertise in accident investigation and forensic engineering.
- Consultants who bring their specialist materials science knowledge to investigations.
- Access to specialist equipment across the University of Southampton, including state-of-the-art imaging facilities.
- Capability to design bespoke tests and recreate complex in-service conditions.
The outcome: improving gyroplane safety
The data we provided was included in the AAIB’s investigation report and provided the evidence base for four recommendations to the Civil Aviation Authority. Through design, training and regulatory changes, these recommendations aim to reduce the risk of similar catastrophic failures in the future.
You can read the recommendations in full in the AAIB’s report.
