A poster on another forum turned up the following info for me :-

Oxford R5957 (Mk I) of 14 FTS, crashed Monday 27th February 1941.
Halley : Turned after night take-off and flew into ground 1m N of Sibson, 27.2.41

14 FTS ORB : Cranfield
27/2/41 Oxford R5957 crashed at Sibson RLG during night flying. Both the instructor and pupil F/O M I F Green and LAC D C Ellerbeck were killed
1180

BCPASPA : 86658 Flg Off (Plt Instr) Maurice Ivan Frank Green, RAFVR, 26, of Norwich. ACA. Norwich (The Rosary) Cemetery, Norfolk.
928881 LAC (Plt U/T) Douglas Charles M Ellerbeck, RAFVR. Sandy Cemetery, Bedfordshire.

The primary source above is the units Operations Record Book (ORB).

I wonder if I could ask a favour. If anyone is passing through Sandy at some point, could they get me a photograph of LAC Ellerbecks grave ?