Often, we can choose between flying an ILS or RNAV (GPS) to a particular runway. But when the minimums are the same, how do you choose? Like many aspects of aviation, it depends. Generally, though not always, I prefer RNAV approaches.
ILS signals, which require transmitters and antennas on the ground, seem more susceptible to issues than GPS. For example, in March 2019, signal issues, caused by 2 to 5 feet of snow around the localizer antenna, led CommutAir Flight 4933 to touch down in snow to the right of the runway at Presque Isle, Maine (KPQI). Also, notes on ILS charts sometimes state that an autopilot cannot be used below some altitude on the approach. Those usually originate when problems are detected during routine test flights by an FAA flight check aircraft.
