Shouldn’t there be an automatic cross-check between the pitot and GPS to see if there’s a major disagreement?
You would think. When I took instrument training the point was to scan key instruments, airspeed, altimeter, vertical speed indicator, heading indicator, artificial horizon etc, and not rely on just one. They were in extreme turbulence though, all hell must have been breaking loose.
Nope - disagreements between pitot and GPS are to be expected.
I’m not a pilot, but in other threads that have discussed this issue, those in the know say that GPS will only give you ground speed. And ground speed is very much different than airspeed. Airspeed is the key. It lets you know how much air you got passing over the wings. With a strong tailwind, your GPS will show great ground speed, but if you’re not passing enough air over the wings to create lift (airspeed), you’ll stall.
That doesn’t work too well. One measures air-speed, the other ground-speed. The winds encountered at high altitudes can cause a major difference.