GPS Status = 4

From ardupilot/AP_GPS/AP_GPS.h

 /// GPS status codes
    enum GPS_Status {
        NO_GPS = GPS_FIX_TYPE_NO_GPS,                     ///< No GPS connected/detected
        NO_FIX = GPS_FIX_TYPE_NO_FIX,                     ///< Receiving valid GPS messages but no lock
        GPS_OK_FIX_2D = GPS_FIX_TYPE_2D_FIX,              ///< Receiving valid messages and 2D lock
        GPS_OK_FIX_3D = GPS_FIX_TYPE_3D_FIX,              ///< Receiving valid messages and 3D lock
        GPS_OK_FIX_3D_DGPS = GPS_FIX_TYPE_DGPS,           ///< Receiving valid messages and 3D lock with differential improvements
        GPS_OK_FIX_3D_RTK_FLOAT = GPS_FIX_TYPE_RTK_FLOAT, ///< Receiving valid messages and 3D RTK Float
        GPS_OK_FIX_3D_RTK_FIXED = GPS_FIX_TYPE_RTK_FIXED, ///< Receiving valid messages and 3D RTK Fixed