12 October 1956. Sub Lt R Davies, a Fleet Air Arm trainee pilot stationed at RNAS Dale in Pembrokeshire, was barely ten minutes into an evening training flight – flying in cloud on instruments – from RAF Valley on Anglesey, when he crashed into the top of Mynydd Mawr. The impact of the crash killed him and wreckage from the Vampire was flung over the summit ridge and down into Cwm Planwydd.
Photo above is looking towards the coast near the impact point. Photo below shows some of the remaining debris in Cwm Planwydd with Moel Eilio and Foel Gron beyond.