L4873 was one of three Blenheims flying in formation on a training exercise from RAF Upwood near Huntingdon. The flight plan took the formation out to the Isle of Man before returning to Cambridgeshire, but over Wales they flew into cloud.
The procedure upon entering cloud was for aircraft to break formation and climb out of it. It seems the pilot of L4873 instead chose to dive out of the cloud to try to maintain visual contact with the ground, alas with fatal consequences; the Blenheim crashed into Foel Wen in the Berwyn mountains with the loss of all on board.
Sergeant M C Cotterell, pilot
Sergeant R J Harbour, obeserver
Aircraftman, second class, K C Winterton, wireless operator/air gunner.