GPS Backup Strategies

In the October 2015 issue of IFR, I noted that the VOR reduction plan included a provision for something called the Minimum Operational Network, or MON. The FAA says that MON is specifically aimed at lower-end GA IFR aircraft in case of a GPS outage. I added that MON is a transitional strategy to get to something called APNT, or Alternate Positioning and Timing. Lets dig into this and explore the GPS backup support you can expect in the future as we transition from terrestrial to satellite navigation.

Fred Simonds

Wednesday, January 13, 2016 at 12:00 AM ET

Verified

Key Takeaways:

The FAA's Minimum Operational Network (MON) is an interim GPS backup strategy for lower-end GA IFR aircraft, scaling down VORs but ensuring coverage and designating MON airports with GPS-independent approaches.
MON VORs will have expanded service volumes, allowing pilots to navigate to a MON airport (within 100 nm) in the event of a GPS outage, with this system planned to remain operational until at least 2025.
Beyond VORs, the FAA is enhancing and adding DME stations to provide GPS-independent Area Navigation (RNAV) capabilities, particularly for higher altitudes and more sophisticated aircraft.
The ultimate long-term solution is Alternate Positioning and Timing (APNT), which aims to provide full PNT (Positioning, Navigation, Timing) capabilities using NextGen infrastructure, such as enhanced DME or pseudolites, to seamlessly back up GPS.

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In the October 2015 issue of IFR, I noted that the VOR reduction plan included a provision for something called the Minimum Operational Network, or MON. The FAA says that MON is specifically aimed “at lower-end GA IFR aircraft in case of a GPS outage.” I added that MON is a transitional strategy to get to something called APNT, or Alternate Positioning and Timing. Let’s dig into this and explore the GPS backup support you can expect in the future as we transition from terrestrial to satellite navigation.

Where GPS Stands Today

Statistics show that both GPS and WAAS have been extremely reliable. The last GPS outage due to an ionospheric sunstorm was in 2006. Today there is not just one GPS signal, but three, and there will be a fourth in 2017. The latter two signals are in the highly-protected Aeronautical Radio Navigation Services band. These signals are more resistant to interference and jamming than before.