GPS jamming is radio frequency interference that disrupts the ability of a receiver to track the GPS signal and provide an accurate position solution. GPS jamming can be either intentional or accidental. Jamming can overwhelm the GPS receiver and prevent it from determining a position. Jamming can also partially degrade the signal so that only a few satellites are available for the receiver to compute a position with reduced accuracy.

A strong jamming signal could cause loss of GPS positioning, resulting in FMS degradation, ADS-B Out failure, and the loss of SVT and forward looking terrain alerting functions. Upon a loss of GPS positioning due to jamming, ADAHRS will revert to the No-GPS Mode and will continue to provide attitude and heading information with no noticeable adverse effects on accuracy.

The flight director mode will transition to a reversionary state if the loss occurs while FMS is in use for a GPS based approach; otherwise, the flight director mode can remain coupled to the FMS for lateral and vertical modes.

When GPS is lost due to jamming, the pilot should use alternate navigation methods such as VOR, LOC/ILS, or an ATC-assigned heading, if possible, instead. See the previous discussion on FMS Positioning Sensors in this section for more information.