L-1011 Navigation: Inertial Navigation System (INS) (34-43-3)

Before the INS can begin operation, the platform must be aligned to true north. When power is applied and the gyros come up to speed, the playroom is erected just as a conventional attitude gyre is erected. Once the platform is erect, the accelerometers sense the earth's rotation. The computer determines the direction of motion caused by the earth's rotation relative to the platform axis. In doing so, the computer determines the orientation oft he platform to true north. It is useful to remember that all computer computations are in reference to true north.

After orientation to true north, the computer measures the rate of earth rotation. By comparing the measured earth rate to earth rate data stored in the computer's memory, the computer can determine its latitude. However, the INS cannot determine its longitude. Before navigation can commence, the crew must insert the coordinates at which the platform is erected into the computer's memory.