Abstract: A warning system for aircraft compares the rate of descent of the aircraft with its altitude above ground after take-off, and generates warning if the aircraft is experiencing an excessive descent condition for the radio altitude at which the aircraft is flying. The position of the landing gear, the speed of the aircraft and the engine power are mointored to enable the system only during the take-off or missed approach phases of operation in order to minimize false warnings during other phases. The relationship between radio altitude and descent rate required to generate a warning is optimized for small, high performance aircraft such as fighter or attack aircraft.

Abstract: A data communication system for an aircraft includes a voice encryption unit that is selectably included in the audio path between a user and a radio. The data communication system is interconnected so that the unencrypted audio path of a user is isolated from other users, thus providing the user with a secure, private communications link within the aircraft, as well as between the aircraft and a ground station. The system includes an audio path from the cockpit to the encryption unit and an audio path from the passenger cabin to the encryption unit, and further includes a control unit in each of the cockpit and the cabin so that control of the encryption unit can be selectably switched between the cockpit and the passenger cabin.

Abstract: A borehole survey instrument has a probe with a polarized light system for transmitting a signal representing the angular orientation of the probe to the surface. Light from a source in the probe is directed through a polarizing filter with an axis of polarization orthogonal to the longitudinal axis of the probe. The polarized light beam is transmitted to the surface through an optical fiber light conduit. The angle of polarization is detected with a rotating polarizing filter and provides a measure of the probe orientation. In surveying a borehole, azimuth is determined from inclinometer measurements. The probe orientation in vertical sections of the borehole is measured by the polarized light system. Two measures of borehole azimuth are combined, providing an improved measure of azimuth in boreholes near vertical and near horizontal.