There's a story (I think it was in one of Ernest Gann's books) of a Catalina crew flying in IMC over Greenland during World War 2 when their airspeed gradually reduced to near zero despite their having full power applied on the engines. Amazingly, they'd flown - very, very smothly - into a very gently rising snow-covered hill and the aircraft (and very surprised as well as very, very lucky crew) ended up stranded on the snow drift for quite a few days before they were rescued.
Is it possible this incident was along the same lines?