Anti icing system is not certified for LSD larg supercooled droplets , freezing rain , freezing dreezle. LSD is probably what they encountered.
Blocked pitot tube including moisture drain hole if the AC was put in climb will read high erroneously and if you fixate on IAS and not flying pitch/power the reaction would be NU input and going into stall.
Here is what happened to North West B 727 in 1975
,,Investigators found that the
pitot heads had
ce damage which caused the crew to receive the wrong readings. The crew, believing the readings where true, raised their nose and pulled back on the
control column, which caused the plane to stall,,
,,The aircraft had descended from 24000 feet to 1090 feet in 83 seconds,,
Full NTSB report
http://libraryonline.erau.edu/online...s/AAR75-13.pdf