Are panel mounted GPS receivers recommended over handheld receivers when used as a reference for autopilots?
Most handheld GPS receivers update and provide output data (NMEA 0183) only once every two seconds. Panel mount receivers update and provide output data (Aviation Data Link) once per second. Therefore, panel mount receivers talk to the autopilot at least twice as often and provide it with more current position and situational data. It follows, then, that the autopilot will be somewhat more responsive when coupled to a panel mounted GPS. In most cases, when closely tracking the course centerline, you will not notice any difference. However, if you are turning at a 3 degree per second rate the aircraft can turn 6 degrees between updates if you are using a handheld GPS. One place this may be noticeable is in the PCS (Pilot Command Steering) mode – i.e., If you engage PCS, enter a steep turn and then release the button, it is possible to have several degrees of overshoot if you don’t level the plane and wait for the next GPS update before releasing the button. There are predictive anticipa
