|From Walker's "Canadian Military Aircraft Serial Numbers" site.... H21 Serial # 9613. Looks like it occurred in 1956 :
first date: 15 October 1954 - Taken on strength
With No. 108 (CR) Com Flight at RCAF Station Bagotville, PQ from fall of 1954, for pilot training before H-21B arrived at this Unit. To No. 121 (Composite) Flight at RCAF Station Sea Island, BC in December 1955. Crashed in BC interior on 21 April 1956, killing 2 RCAF crew and a Vertol tech rep.
last date: 17 May 1956 - Struck off
Hope that gets you started.