GPS vs. Pitot-Static alt/AS

[swatson999]

This may have been answered before, but a quick search didn't turn up anything...

What happens if the pitot/static system altitude and/or airspeed don't gibe with the GPS data? For example, you're flying along in the soup and *wham* a chunk of ice plugs up your pitot tube. It'll be okay for a while, until you change altitude or power settings, then the GPS data should start to diverge from the pitot-derived data.

Will you get a warning? Similarly for altitude...say your static line got blocked somehow.

Just curious...a side-topic to a discussion elsewhere about backup systems (and it seems a lot of people are afraid to let go of round gauges ).

 

[Dynon]

Our products do annunciate GPS ASSIST when airspeed is lost due to pitot icing or some other blockage that disables airspeed entirely (when it goes to 0). Detecting more subdle effects gets harder quickly when you consider that there are many attainable normal flight configurations (high winds aloft for IAS/GPS mismatches, bad GPS lock or badly set baro for altitude mis-matches) that can look like failures. And spurious nuisance alerts, even if they don't happen *that* often, are bad, because once you get into the habit of ignoring an nuisance alert, you've diminished the entire purpose of the alert. We do also annunciate when flight instruments from different ADAHRS disagree, and multiple ADAHRS can be plumbed into different pitot and /or static sources to gain some more redundancy this way. Most people don't equip this way, even in certified piston single land, mostly because when you're analyzing the consequences of faults, you have to determine what the consequence is. Not having IAS or altitude is definitely not ideal, but it's also something that is not considered a catastrophic failure in almost any circumstance.