De-ice

De-ice is a mechanism that de-ices the enigines and control surfaces so that air can flow over them properly. If they are icy and air flows over them abnormally, the control surfaces won't be as effective.

Pitot heat is a mechanism which prevents ice build up on static ports, i.e. sensors that sense altitude, speed etc. Clearly ice would block these ports and it would most likely end in disaster, as did happen once with an Aeromexico 757 when someone forgot to remove the protective foil they put on them after maintainence.

In FS, I think it depends on your realism settings but in FSpax make sure you always put on pitot heat becasue otherwise you speed tape goes haywire ❗ ❗

😉

Ya I forgot to put my DE-ICE Switch to ON and when I was at 31,000 ft it was about -17* (winter) and I just started to fall out of the sky and my engines shut down

you should always have a backup plan jester...

...like an open window and lots of hot coffee, lol 😂