I can't find a source for this right now, but I believe that the pitot tubes were only iced over briefly, and that normal airspeed readings did resume long befo

I can't find a source for this right now, but I believe that the pitot tubes were only iced over briefly, and that normal airspeed readings did resume long before the end, but it seems the crew never reached any state of confidence about whether (or which of) their instruments were correct. It raises an interesting point about instrumentation - it's easy to make a display that looks like a gauge, a needle, or whatever. But if the system behind the display can have some knowledge of whether it's getting good data or not, then really there is (at least) another dimension to the information. How do we represent that so that operators can make sound judgements in unfortunate circumstances?