Although GPS interference has been a factor for many years now, especially in the Mediterranean region, pilots have had the challenge to identify that the GPS signal has been lost. There is no alerting function on the flight deck to inform pilots of GPS jamming, just a series of system malfunctions which provide clues to the problem. These malfunctions can include the aircraft clocks running backwards, the loss of ADS-B, ground proximity alerts (regardless of altitude) map shifts- etc. EASA has issued a series of safety bulletins on the subject and the latest one can be found here.
Whilst there are many examples of GNSS jamming, impacting the core constellation and external augmentation systems, from low powered localised jammers (commonly known as personal privacy devices (PPDs), and which are illegal) to military grade wide area jammers, a new issue has arisen since October 2023. This is GPS spoofing, where false signals are injected into the receiver. This can have a large variety of effects on aircraft avionics. Spoofing can cause some receivers to lock up, some receivers to produce false position and time outputs while other aircraft automatically revert to alternative navigation sources. The aviation spoofing observed to date has caused large GPS position jumps and is therefore easily observed by aircrew. Typically, most aircraft will continue normal and correct navigation using INS/IRU. However, in some cases, false GPS receiver outputs have also impacted the INS/IRU position. In all cases, pilots are faced with a good number of system malfunction alerts. Spoofing is commonly due to anti-drone electronic warfare and the impact on civil aviation is collateral, however, when it occurs it can pose significant challenges for the flight deck and for ATC.
It is highly important that both pilots and controllers are aware of, and understand, the impact of GPS jamming and spoofing. Pilots should be capable of operating their aircraft without GPS information and controllers should know their contingency procedures if the pilots report loss of GNSS or loss of position information.
There are some very good videos in the public domain showing the challenges the flight deck face and a couple of them can be accessed here: