GPS Jamming on an IFR Departure from Muscat
You are departing Muscat (OOMS) at 06:00 local on an IFR clearance to a destination 220 NM away. The aircraft is equipped with a single GNSS receiver and a VOR/ILS receiver; the aircraft has no DME. The departure procedure requires tracking a VOR radial to intercept an airway. Ten minutes after departure, the GNSS position flag drops to 'no integrity' and the map freezes. ATC has not reported any jamming. You are in IMC at 9000 ft, 35 NM from the VOR, and the airway ahead requires a 40 NM leg to the next waypoint. The VOR receiver is serviceable and the VOR is within range.
1. Assess the navigation situation and determine what you can and cannot use for navigation.
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Loss of GNSS integrity means the receiver cannot guarantee the position is within the required accuracy, so it must not be used for IFR navigation. The map freeze is consistent with a receiver fault or interference. ATC has not reported jamming, but GNSS interference is possible and may be localised.
The VOR receiver is serviceable and the VOR is within range at 35 NM, so you can navigate using VOR radials. However, without DME you cannot determine distance from the VOR directly; you can use radials and crossing radials from a second VOR if available, or time-and-heading calculations. The 40 NM leg ahead can be flown on a VOR radial if the airway is defined by the VOR, but you must confirm the airway structure from the chart.
You cannot rely on the GNSS for the airway or for the destination approach if it requires GNSS. You must inform ATC of the loss of GNSS and request vectors or a VOR-based routing.
2. State the communications and operational procedure you would follow, including the request to ATC.
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Advise ATC immediately: 'OOMS, [callsign], we have lost GNSS integrity, request VOR-based routing and vectors as required.' ATC can provide radar vectors and monitor your progress. Request confirmation of any reported GNSS interference in the area.
Operationally, revert to conventional navigation: tune and identify the VOR, track the appropriate radial, and use timing to estimate distance. Cross-check position with the VOR and, if available, a second VOR. Do not attempt to use the frozen GNSS map for navigation.
Plan for the destination: if the approach requires GNSS, you must either divert to an aerodrome with a VOR or ILS approach, or hold and attempt to restore GNSS integrity. Given the aircraft has an ILS receiver, an ILS approach is a viable option if the destination has one. Update the fuel plan accordingly and inform the operator.