+2c to +12c
In the RAF aircraft, the overall critical temps for the anti-icing to go on was between +2 to +12C. There was a further stricter restriction which applied if the temp was in the +2 to +6 range. My memory from 46 years ago must have offloaded some of the detail but it may have required a speed restriction or possibly another level of anti icing kit being switched on. Does any of this prod Brakedwells memory? As I recall we slowed down so that the kinetic heating reduced and the OAT then fell below the +2c critical figure. If it were then say, -1C you didn't need the anticing on. ....... so you took it off and promptly accelerated back into the +2 to +6C range......Catch 22.
Not much help I'm afraid, but nostalgic to recall a job I'd have had without pay. The saddest day of my life when they axed the aircraft.