BOAC - I stand corrected. Had I taken the time to turn the page in the FCOM, I would have seen the reference..obviously I don't fly the type. At least in the generic FCOM that I have, it is under Supplemental Procedures for Anti-Ice and Rain. As you have pointed out, there is a good description of this in a previous thread.
That does not change my comment regarding the Saab. They do not have any such procedure regarding upper wing surface ice.
With respect to Miss Terry's question,
"My question relates to any icing on the upper surfaces, not necessarily that caused by cold fuel.
The example would be arrival at an aircraft first thing in the morning to find a heavy frost has formed on the wings. Could departure without deicing be permitted on any type at all ?."
The Boeing 737 NG procedure refers to 1/16 inch frost within the marked area of the upper wing surface, as well as an outside temperature that is above freezing. I suspect that any frost that forms for reasons other than cold soaked fuel will not lie within the marked areas, and is unlikely to survive long after the temperature rises above freezing. As to whether 1/16 of an inch corresponds to "heavy frost", well, I've sat in way too many industry/authorities meetings to open that can of worms. I would only suggest that the underside frost limit has been 1/8 inch for quite a while now.
Suffice that the only current allowance for upper wing surface frost is in the case of cold soaked fuel, and then is limited to the 737 NG. Further, none of this is allowable under FAR 121.629, so it is a moot argument in the States.
I'll dig around with the certification folks and see if anyone else is approaching this the same way.