It's not either/or you need both; sometimes "The Machine Stops".
REF: H0524/12 From: 2012-Mar-26 Mon 07:00 To: 2012-Mar-30 Fri 16:00
Schedule: 0700-1600
ICAO: EGTT SFC to 40000FT AMSL
GROUND AND GPS JAMMING WI 54NM RADIUS OF 5229N 00045E (STANFORD
TRAINING AREA, CAMBRIDGESHIRE). AIC P 009/2012 REFERS. CTC 0207453
6530/6535 OR STANTA RANGE CONTROL 01842 855235. 12-03-0017/AS 4