Simon Glancey has submitted the following:
Sgt. Mullin was killed when Armstrong-Whitworth Whitley III K9001 of 51 Squadron was lost on a ferry flight. The Whitley took off from R.A.F. Linton-on-Ouse at 10.50, climbed steeply to around 200 feet, stalled and crashed, killing both crew members. It was discovered that the elevator locks had not been removed before the flight.
Royal Air Force Bomber Command Losses of the Second World War: 1939-1940; W.R. Chorley; 1992; Midland Counties Publications; ISBN 0 904597 85 7, page 16
He is remembered in Blackhill on B145.01 where his name is given as "Mullen", and in Consett on C101.01 and C101.12