The work is devoted to the problem of development of backup strapdown attitude control system (BSACS) based on micro-mechanical sensors. A block diagram is proposed for constructing a system based on micromechanical accelerometers and gyros whose complex processing of signals is realized by means of a Kalman filter operating in steady state. Dependencies of the filter parameters on the accuracy of the sensors used are shown. The design relationships are given, which allow us to calculate the filter parameters by the technical characteristics of the sensors used. The work presents a study of the inertial measurement module, based on micromechanical gyroscopes MMG-APTRON (Central Research and Development Institute Electropribor Corporate Group JSC), ADXRS-642 (Analog Devices Co.) and compensation accelerometers АТ1104 (ANPP Temp-Avia JSC). There presented the design of the measurement module for the construction of a backup strapdown attitude control system, which may be applied both on unmanned aerial vehicles and as a backup system on piloted aircrafts. The results of tests of the developed system based on FSUE "GosNiIi AS" are given, which showed that BSACS provides pitch and pitch angles with an error of no more than 2 degrees with a straight flight and no more than 3 when maneuvering. The influence of the misalignment of the BSACS axes and the mobile object on the accuracy of the development of angular parameters is shown. A method for algorithmically accounting for axial misalignment is proposed, which makes it possible to reduce the requirements for the accuracy of alignment of the axes. The reasons for the increase in the BSACS error during maneuvering are shown. A method for increasing the accuracy of a system based on an analysis of the modes of motion of an aircraft is proposed. The results of modeling the method of increasing the accuracy are given, which show that the error of BSACS during maneuvering, in some cases, can be reduced by more than 3 times.