CONTINUOUSWAVE

I don't want to find out I'm 25 miles inland at an airport when I think I'm on the water. It is then that I wouldn't trust my GPS receiver.

http://galileognss.eu/mass-gps-spoofing-attack-in-black-sea/

Regarding the incident in the Black Sea in June when a number of ships reported that their GPS position showed them at a local airport, informed and expert analysis of the incident links it to a visit by Russian President Vladimir Putin to the area, which was in the vicinity of the ships affected. These same experts suggest that the purpose of the spoofing was to act as a geo-fence for drone flights. Some drones apparently are manufactured with an on-board control system that will inhibit them from flying near airports. Thus any such drone in the vicinity of Putin would have been prevented from flying. Similar events have been noted in Moscow near the Kremlin. Smartphone users found their devices' GPS receivers showed they were at a local airport. Of course, only the consumer-grade drones that have the no-fly-near-airport firmware would be affected. But this would deter the casual drone operator from being able to fly a drone in the area where Putin might be located.

For background on GPS spoofing and some insight into this Black Sea incident, see

http://gpsworld.com/spoofing-in-the-black-sea-what-really-happened/

http://gpsworld.com/pnt-roundup-telecoms-cite-gnss-vulnerabilities/

https://nrkbeta.no/2017/09/18/gps-freaking-out-maybe-youre-too-close-to-putin/

Here is newer information on the Black Sea spoofing incident. The latest GPS WORLD magazine edition (November 2017) mentions that an informed reader comments:

We have been following this case for quite some time now. We track all merchant vessels worldwide on the basis of Automatic
Identification System (AIS) 24/7.

The spoofing is still going on. Even today ships were placed at the airport runway. In total over 600 vessels were placed on the runway since early June. Our preliminary conclusion is that the 'spoofing' is probably NOT done on purpose. The most likely cause of this spoofing is a GPS re-radiator transmitter located in the hanger close to the end of the runway. This device is used for testing GPS when planes are placed inside the hanger. So, line-of-sight interference?