GPS Interference and an RNAV Approach Request at Bandar Abbas
Bandar Abbas (OIKB) approach at 0900 UTC. A NOTAM says GNSS is unreliable within 40 NM due to interference. IRB720, an A320, requests the RNAV (GNSS) runway 21 approach. At 18 NM northeast, the crew reports GPS PRIMARY LOST and asks for vectors. The airport has a VOR/DME runway 21 approach and a serviceable ILS runway 21. Weather is VMC, wind 210/10 kt, visibility 10 km. IRB721 is on 8 NM final for the ILS at 2,500 ft. IRB720's flight management system still displays a GPS position, but the crew cannot confirm RAIM. The controller has radar and VOR/DME monitoring. The adjacent military control unit has also reported GPS jamming on the same frequency band. The controller must decide whether to clear the RNAV, vector for the ILS, or send the aircraft to the VOR.
1. Can the controller clear IRB720 for the RNAV (GNSS) approach? Explain the navigation and regulatory reasoning.
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No. An RNAV (GNSS) approach depends on GNSS as the navigation sensor, and the crew must have the required equipment, a valid RAIM prediction, and the ability to meet the approach's performance requirements. The NOTAM already warns that GNSS is unreliable within 40 NM. The crew reports GPS PRIMARY LOST and cannot confirm RAIM. The fact that the flight management system still shows a GPS position does not prove the position is valid; it may be a frozen or degraded solution. Under these conditions the controller should not issue an RNAV approach clearance. The correct action is to offer a conventional approach that does not depend on GNSS, such as the ILS or the VOR/DME runway 21, subject to aircraft equipment and minima. This is a navigation-integrity decision, not merely a preference.
2. How should the controller sequence IRB720 with IRB721 and issue the new clearance?
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IRB721 is established on the ILS at 8 NM, 2,500 ft. IRB720 is 18 NM northeast and needs vectors. Keep IRB720 behind IRB721 with at least 5 NM radar separation and do not allow it to cut in front of the established ILS traffic. Vector IRB720 onto a downwind or base that joins the ILS outside the final approach fix, then clear it for the ILS. Phraseology: 'IRB720, GPS interference reported, RNAV approach not available, vector for ILS runway 21, maintain 3,000 ft.' After the intercept: 'IRB720, 5 NM from the final approach fix, cleared ILS runway 21, report established.' If the aircraft cannot use the ILS, offer the VOR/DME approach with the appropriate minima, but sequence it behind IRB721. Advise the crew of the military jamming report and ask them to report any further navigation degradation.
3. What if IRB720 later reports that its only usable approach is RNAV?
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If the aircraft cannot use the ILS or VOR/DME, the controller cannot create a legal RNAV approach where the navigation performance is not assured. The aircraft should be treated as unable to continue the approach and given holding, diversion, or another airport with a non-GNSS approach. The controller should ask the crew to state its intentions and fuel state, and coordinate with the supervisor. Do not accept a pilot's request to 'try the RNAV' when RAIM is not available and a jamming NOTAM is active. If the aircraft declares an emergency, emergency priority applies, but the navigation limitation must still be passed to the crew and to any alternate unit. Record the NOTAM, the GPS PRIMARY LOST report, the approach offered, and the final decision.