# Why does this NOTAM make me think GPS is unavailable?

First: I'm not a real pilot. I used an on-line flight planning tool, and in the brief was the following "GPS NOTAM":

GPS 11/032 ZSE NAV (CHLK GPS 15-15) GPS (INCLUDING WAAS, GBAS, AND
360822N1173846W (BTY214059) FL400-UNL DECREASING IN AREA WITH A
DECREASE IN ALTITUDE DEFINED AS:
DLY 2130-2230
1511172130-1511182230


I must admit I don't understand most of this, but it seems like GPS is unavailable in what seems to be a huge inverted cone of space. What's going on here?

• Interestingly, this appears to be those locations with approximately line of sight toward a ground-based location (the curvature of the earth limits the radius according to altitude). – Greg Hewgill Nov 16 '15 at 22:19
• – mins May 18 '17 at 8:02