Active Frost Conditions
I have read my company’s winter ops and deicing manuals but cannot find a clear answer to the following dilemma.
The other day I took over a 737-800 mid morning on a cold day. It was 2 degrees C and Active Frost conditions. The aircraft had been anti-iced with Type II twice. Once at 0400 and once at 1000. It was now 1100. Full main tanks, tank temperature around 3 degrees C. By the time we were ready, it was 1145 and a well-timed fog bank rolled in. LVPs, VIS less than a statute mile etc. Accordingly to my SOPs, that’s freezing conditions and Anti-icing not strictly required if wings are clean.
The Type II on the wings was still fluid but a contamination check would only be valid for 5 minutes before takeoff. It was a 20 minute taxi. To my mind the Active Frost HOT was no longer valid because of the change in environmental conditions, but I can find no confirmation of this in the manuals. The Type II HOT tables for this make of fluid didn’t specifically refer to fog conditions nor would the HOT for any similar type and intensity of precipitation give us long enough to get airborne (given the 1000 anti-icing start time). In other words the HOT was expired.
I elected to re-do the Type II.
Does anyone have advice on this type of situation or links to appropriate FAA/EASA sources?
I would be much obliged.