Repair of LN-251 INS/GPS Navigation System

The National Oceanic and Atmospheric Administration (NOAA), Aircraft Operations Center (AOC) at Lakeland, FL operates two (2) WP-3D Orion aircraft in support of several operational projects. Each aircraft is equipped with a Multi-Mode Radar (MMR) and within it, an LN-251 INS/GPS Navigation System. INS’s are navigation devices that use accelerometers, gyroscopes and a computer to continuously calculate by dead reckoning the position, the orientation, and the velocity of a moving object without the need for external references. The INS must initially align itself with its position and velocity from a known source accompanied with the initial orientation. After alignment, the INS computes its own updated position and velocity. Two of AOC’s LN-251 units fail to align and require servicing.