GNSS jamming during an RNAV approach
An Embraer 175 is established on the RNAV (GNSS) Runway 24 approach at a regional airport, 6 NM final, cleared to land. LNAV minima are 520 ft; the reported ceiling is 700 ft with 3 km visibility. At 5 NM the crew reports 'GPS PRIMARY LOST, RAIM UNAVAILABLE, going around'. The ILS for Runway 24 is serviceable. A second aircraft, 15 NM northeast, reports 'GPS jamming, map shifting'. The airport has no radar; approach uses ADS-B. A NOTAM in the briefing folder warns of GNSS interference from a military exercise 40 NM away, active until 18:00. Another arrival is 12 NM final on the ILS. The Embraer has 45 minutes' fuel. You are working approach and tower combined.
1. What do you instruct the Embraer to do, and what do you need to ask?
Read the worked answer
Acknowledge the go-around and protect the missed approach immediately: 'Climb to 3,000 ft, turn right heading 090, radar vectors ILS Runway 24.' Do not clear it for another RNAV approach. Ask: 'Confirm fuel endurance and intentions.' Forty-five minutes is enough for one ILS plus a diversion, but confirm.
Then vector it onto the ILS, give the localiser frequency and check that the crew is able to fly the ILS. The key point is that the pilot has lost GPS integrity (RAIM), so the RNAV approach is neither legal nor safe to continue; the go-around is correct, and ATC must not pressure the crew to continue visually. If the crew requests a visual approach, a 700 ft ceiling and 3 km may permit it, but the pilot must be able to maintain visual reference; do not suggest it yourself.
2. Why can the RNAV approach not continue, and how does the second aircraft's report change your management?
Read the worked answer
An RNAV (GNSS) approach requires on-board performance monitoring and alerting. If RAIM is unavailable, the system cannot guarantee the integrity of the navigation solution, so the approach minima cannot be assured. The pilot must not continue past the final approach fix, and ATC should not clear another aircraft for the RNAV approach while the interference persists.
The second aircraft's 'map shifting' at 15 NM confirms wide-area GNSS interference, not a single receiver fault. Treat the airspace as GNSS-degraded: ask all arrivals whether they are GPS-equipped and able to fly the ILS, sequence the ILS arrivals, and expect some aircraft to be non-RNAV capable and give them vectors or holds. Do not assume the interference is over until it is confirmed.
3. What notifications and warnings should be issued, and by whom?
Read the worked answer
The ANSP should notify the IAA as a mandatory occurrence if the interference affected the safety of an aircraft; a GNSS jamming event that disrupts an approach is reportable. The airport operator and AIS should issue a NOTAM warning of GNSS interference in the area, and the ATIS should carry a warning.
ATC should inform the military exercise control unit that the interference is affecting the approach and ask for confirmation or cessation. The MET office is not relevant here; this is a navigation and radio interference matter. If the interference is malicious, the communications regulator and An Garda Siochana may need to be informed. The controller's job is to warn, protect and report, not to diagnose the source.