Abstract: The invention is a process and a device for determining an estimation of the altitude of an aircraft from at least two independent measurements of the altitude, by polling. The aircraft must include at least one inertial reference system. A signal representing a first or second derivative of the altitude is diverted from the inertial reference system, polling is undertaken on the magnitudes of like order deduced from the independent altitude measurements and from the derivative of the altitude, respectively, and an integration operation is undertaken so as to obtain the altitude estimation.

Abstract: A device is disclosed for controlling a variable electric signal. A first switch receives the monitored variable electric signal at its input. A second switch receives a first limit electrical signal for the monitored signal and a first minimum reference for the first limit electric signal. A third switch receives a second limit electric signal for the monitored signal and a second maximum limit reference for the limit electric signal. The first switch delivers at its output: the monitored signal when it is between the output signals of the second and third switches; the output signal of the second switch when the monitored signal is greater than the latter signal; and the output signal of the third switch when the monitored signal is less than the latter signal.