During a local flight to practise aerobatics, the pilot reported that shortly after he commenced his routine the engine began to run roughly and the available power “dropped off”. The pilot selected the mixture to RICH and the electric fuel pump ON, but there was no improvement in the engine’s performance. He carried out a forced landing in the only available field, which had a 30° upslope and contained sheep. The aircraft was substantially damaged but the pilot, who was uninjured, was able to vacate normally.
The constructor and maintainer of the aircraft commented that an initial inspection of the engine did not reveal any defects. He considered it was possible that, during the aerobatic manoeuvring, air may have been ingested into the fuel supply system and, due to the length of pipework on this particular model, it may have taken time to clear.
Further work is planned to inspect and fault-find the engine and fuel system. If there are any relevant findings they will be reported in a future AAIB Bulletin.