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 is implementing the Minimum Operational Network (MON) as a transitional GPS backup for lower-end GA IFR aircraft, utilizing a scaled-down VOR network (about 650 VORs) and designating around 200 MON airports with GPS-independent approaches.
MON VORs will feature an expanded service volume, and the plan also includes enhancing DME infrastructure to support GPS-independent Area Navigation (RNAV) for various aircraft and altitudes.
Beyond MON, the long-term strategy is Alternate Positioning and Timing (APNT), designed to provide full PNT (Positioning, Navigation, Timing) capabilities independently of GPS.
APNT options include reconfiguring the DME network (NextGen DME) and exploring ground-based pseudolites to create a robust, interference-resistant backup ensuring seamless navigation during GPS outages.

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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.