Article in the Aeroplane June 2017, Issue 230, gives details of the Military Sponsored Air Service in which RAF crews were trained on BEA Viscounts to fly the corridors empty in times of heightened tension with the USSR.
Crews were trained at the BEA facility at Heathrow which consisted of basic simulator training and two familiarisation flights of about 5 hrs total. I was the navigator on a crew with two pilots drawn from the Handley Page Hastings at RAF Colerne. It was a rapid conversion course for the pilots who were not turboprop trained and I was rather glad that we did not do it for real due to our lack of familiarisation and experience with the Viscount.
We operated from Templehof airport and flew, as observers, with the BEA crew and flew each of the three corridors on two separate occasions.
I believe RAF crews drawn from the Brittannia and Argosy fleets also took part as did Comet crews who, I believe, were converted to BEA BAC 111's when the Viscounts were withdrawn from service.