A misty, eerie 9 mile walk for 14 ramblers from Tafarn Ty Uchaf (Top House), Trefil to a Wellington Bomber crash site...followed by a poignant memorial service, conducted by Alan Hancox. History On December 9, 1940, a Vickers Wellington Bomber (Serial T2520) crashed into the mountainside at Cefn yr Ystrad, just north of the village of Trefil, killing all six crew members on board. The aircraft, belonging to the No. 115 Squadron based at RAF Marham, was returning from a successful bombing raid over Bordeaux, France. Due to severe weather and primitive navigation equipment, the crew mistook the mountainous terrain of the Brecon Beacons (Bannau Brycheiniog) for the flat lowlands of East Anglia and struck the rocky ridge at 3:12 AM.