Email Thread from Brian H

Date: Sept 7 2019
Subject: GPS Outages Affecting ADS-B - Show Topic?

UCAP Gang,

Out here in the West, we often see NOTAMS for planned GPS outages. Indeed, I have experienced GPS outages in SoCal and Nevada in my day job flying the A320. Equipped with INS, a short-term GPS outage is not much of a concern.

However, for GA, a GPS outage can be a concern as it has implications for ADS-B out, required effective January 2020. It is my understanding that in early July the FAA published a policy interpretation to the Federal Register (which I now cannot locate) stating that it is the pilot’s responsibility during preflight to verify that a reliable GPS signal will be available to their ADS-B out units for reporting position information. If a pilot is found operating without a reliable GPS signal for ADS-B out to report the required position information to ATC, he/she can be found to be in violation.

After GA groups raised a concern, the FAA responded that we need not worry, since all certified ADS-B out equipment is WAAS-capable. They also stated that they had a website pilots could check to keep up with GPS outage NOTAMS. However, what does it mean when the NOTAM specifically states that it applies to WAAS and ADS-B? Further, the last time I went to the FAA’s website, there was no information.

Here is a NOTAM I pulled today (9/7/19) for a flight I am planning from KVGT (North Las Vegas) to KRNO (Reno). According to this NOTAM GPS, including support for WAAS and ADS-B, may be unavailable from a time period between 11:30 AM to 3:30 PM on 9/7 though 9/8 - Saturday and Sunday. The radius of the affected outage is 148NM at 10,000 MSL, and 111NM at 4000 MSL, centered 34NM northwest of the HEC VOR, which is in the high desert between Los Angeles and Las Vegas.

GPS 08/8214 NAV GPS (NTC GPS 19-45H) (INCLUDING WAAS, GBAS, AND ADS-B) MAY NOT BE AVBL WI A 270NM RADIUS CENTERED AT 352119N1163405W (HEC 339034) FL400-UNL, 221NM RADIUS AT FL250, 148NM RADIUS AT 10000FT, 111NM RADIUS AT 4000FT AGL, 87NM RADIUS AT 50FT AGL. DLY 1830-2230 1909071830-1909082230

If I understand the FAA’s interpretation and enforcement intentions correctly, a NOTAM such as this, if applied in January, will effectively shut down GA in the entire Las Vegas area and the Southern California basin during the designated time period. This affects a large segment of GA.

And this is not the only GPS outage NOTAM in effect during the proposed flight. My preflight briefing included 13 such NOTAMS centered on various locations and effective at various times of day, and all of which specifically note that ADS-B will be affected.

Either I am not understanding something, or the FAA and the alphabet groups need to come together and sort this out before January 2.

You guys appear well connected and have an ability to dig out this information, and this might be a good topic to address if there is interest from your listeners.

As always - enjoy the show. Happy 13th!

Brian H

Date: Sept 10 2019
Subject: Follow Up on ADS-B Compliance

Hello Jack,

Found it. Regarding the email I sent on the ADS-B compliance and GPS outages, here is a link to AOPA. I still do not see where the NOTAMs that state that WAAS and ADS-B are affected is addressed.

Brian H

Date: Sept 10 2019
Subject: GPS ADS-B Outages


This might answer the question:

Brian H