Release to Service
Turnbull,
Assuming that there were no changes in the RAF RTS, which we are still waiting for, the CA RTS at AL1 (Mar 94) said:
Section Q para 1.1
Instrument flight by day anmd night is permitted within the CGI serviceable and unservicable flight envelopes shown in Figs 1 and 2 with the bank angle limited by the CGI subject to a maximum of 30 degrees.
There were then various other restrictions re minimum speeds, AFCS etc which can be sent to you by PM if you want them.
On icing conditions Section R para 3 says;
Pending resolution of the effect of engine inlet screen blockage on engine surge margins operations in cloud or fog (visbility less than 1000M) or rain are prohited in ambient temperatures colder than PLUS 4C (Indicated)
Para 4 says
Flight in freezing rain is prohibited
Again there is a whole pile more information re operations in snow and use of anti-icing systems etc.
As I recall the forecast temperature for the top of the Mull at the time they took off was below +4C - again confirming, with Tapper's specfic qusetion on breaking the icing limits, that this crew had no intention of doing a cruise climb over the Mull (especially having selected a different waypoint!) and further destroying the whole credibility of the BOI's conclusions.