Aviation emergency instrument, and system initial alignment method and combined navigation algorithm thereof

The invention provides an aviation emergency instrument which comprises an atmospheric pressure measurement unit, an inertial measurement unit, a double-antenna GPS satellite receiver connected with a satellite signal receiving antenna, a graphic display unit, a secondary power supply circuit, and a comprehensive processing and calculation unit, wherein the comprehensive processing and calculation unit receives the information from the individual sensors, calculates the navigation parameters indicative of air speed, pressure altitude, posture, flight direction, longitude and latitude by use of a sensor information fusion algorithm, and sends the calculation result to the high-density liquid crystal graphic display unit. According to the invention, since the aviation emergency instrument can provide the navigation parameters indicative of air speed, pressure altitude, posture (pitch angle and roll angle), flight direction, longitude and latitude, the aviation emergency instrument can not only provide reference information to a pilot who operates the main flight instrument in the normal state but also serve as an emergency instrument in case that the main flight instrument is in the failure state. When the main flight instrument completely fails to work, the pilot can operate the aircraft to return safely by means of the navigation information provided by the emergency instrument.