A transponder having a subsystem for providing an altitude alert function signifying a deviation from a set altitude is described. The subsystem includes an input for receiving an altitude deviation limit associated with the set altitude, a CPU receiving updated altitude and determining a difference between the updated altitude and the set altitude associated with the altitude deviation limit, and a transponder subsystem output device for providing the difference between the updated altitude and the set altitude to a user.
The present application is a continuation application of U.S. patent application Ser. No. 10/378,466, filed Mar. 3, 2003, now U.S. Pat. No. 6,864,830 B1.
The device comprises a means for measuring a dynamic temperature on the outside of the aircraft, a means for determining a static temperature around the aircraft, using said dynamic temperature, a means for determining, using said static temperature and a thermodynamic equation, a second temperature value corresponding to an estimated temperature at said destination altitude, a means for determining the difference between said first and second temperature values, and a means for emitting a warning signal when said difference is greater than a predetermined value.
