What effect would an air-to-air GPS jamming system have? I just noticed an interesting AIC: NOTIFICATION OF GPS JAMMING EXERCISE – HEBRIDES RANGES DURING PERIOD 21 JULY - 1 AUGUST 2014.

PDF available on Eurocontrol (official) or Scribd (mirror).

The Ministry of Defence is planning a GPS jamming exercise:


  Jamming will occur across the 24 MHz bands centred around 1227.60 MHz and 1575.42 MHz. A Falcon 20 aircraft will be equipped with 2 high power jamming pods (1kw), one for each
  GPS frequency.


What effect would this have on a plane entering the jammed airspace?

Related: Can a GPS signal sent to a plane be spoofed?
Jamming GPS means that the GPS receiver is unable to lock-on to the signal from any satellite.

Presumably, pilots of small aircraft would have to revert to more traditional forms of navigation - assuming they have a GPS based navigational instrument or two.

Pilots of airliners would presumably see alerts and (as with most smaller aircraft?) their flight displays would include non GPS sources such as gyrocompasses or magnetic compasses.

I imagine redundant systems would include other sources of position information such as reception of radio-based omnidirectional navigation beacons, inertial navigation systems and looking out the window.