In the early days of the V's, co-pilots had the pleasure of doing engine runs but when I returned in 1970 the engineers had taken them over as well as attempting to run the flying programme and anything else they felt they were entitled to. However one foggy day in Norfolk, with the temperature just above freezing, the rising moan of a Sapphire was heard. There were some anxious looks around the crew-room when the moan rapidly became a roar. The worries were confirmed when the roar was followed by a crump and silenced reigned until the Tannoy announced an engine fire on pan x. In spite of the carborundum on the blade tips the weather conditions were just too much. Moral to the story, just that whoever does the run must be aware of the limitations involved.