InfrquentFlyer 789, "Clearly if above 30kft, we shouldn't be needing a GPWS escape, so maybe disable it. Then what happens if the plane has dodgy altitude info ? Ah, but what's the probability of needing a GPWS escape and at the same time the altitude being screwed ? "
Um, er, ah, please explain how a modern plane could experience dodgy altitude readings over water in the middle of the Atlantic. And do the extent of small thousands of feet even over any place on the face of the Earth. (Small 10s of feet if good DEM data is used along with GPS.)
Now, if you need barometric altitude for aerodynamics purposes I can understand it. However, for the simple task of noticing you are falling very rapidly GPS should be more than adequate for the job as should the ring laser gyros and accelerometers on the plane.
For a couple minutes GPS/Inertial data should be perfectly a adequante substitute for air speed once translated.