No, the GPS is not a reliable backup device. The issue is not latency. Aircraft GPS systems generally update faster than 1 Hz, which is plenty fast for most thi

No, the GPS is not a reliable backup device. The issue is not latency. Aircraft GPS systems generally update faster than 1 Hz, which is plenty fast for most things. The real issue is that GPS gives you the ground speed, and not the airspeed. The wind speeds at 30,000 ft can exceed 200 knots [1]. Therefore, depending on the wind speeds and direction of travel, your airspeed and ground speed can be vastly different. Of course, it is theoretically possible to correct the GPS groundspeed using weather data (would have to be downloaded from external sources) to correct for upper winds, but this is not reliable over much of the surface of the world. [1] http://en.wikipedia.org/wiki/Jet_stream http://en.wikipedia.org/wiki/Jet_stream