Radio Failure in a Procedural Approach Sector
An IFR flight, a B738, is inbound to SBYY on the ILS runway 27. The aircraft is at 7000 ft, 25 NM from the threshold, in a procedural approach sector with no radar. The controller issues a descent to 5000 ft and a clearance to intercept the localizer. The pilot reads back correctly. Two minutes later, the controller calls the aircraft for a position report and receives no reply. The controller tries again on the primary frequency and on the standby frequency, with no response. The aircraft is observed on the controller's flight data display (flight plan correlation only, no radar) as continuing on the expected track. There is another aircraft, a Cessna 172 VFR, in the vicinity at 3500 ft.
1. What are the controller's immediate actions and what assumptions may be made about the B738's intentions?
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The controller should treat the situation as a suspected communications failure and act on the assumption that the pilot will follow the standard IFR communications-failure procedure, not on the assumption that the aircraft is lost.
Immediate actions:
- Continue to try to establish contact: primary, standby, and - if available - the emergency frequency 121.5, and ask other aircraft or the Cessna to relay.
- Protect the airspace: the B738 is cleared to 5000 ft and to intercept the localizer. The controller must assume the aircraft will continue the approach in accordance with the communications-failure procedure: maintain the last assigned level for the last assigned route, then descend in accordance with the published procedure. The controller must keep the airspace below and around the approach path clear.
- Separate the Cessna: the VFR aircraft at 3500 ft is below the B738's cleared level, but if the B738 begins an early descent the vertical margin could be lost. The controller should instruct the Cessna to leave the area or climb/descend clear of the approach path, and inform the Cessna of the situation.
- Notify the approach/area unit and the aerodrome operator, and alert ARFF in case the aircraft lands without further contact.
- Record times and actions.
2. The Cessna pilot offers to fly alongside and report. Should the controller accept, and what are the limits of that relay?
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The controller may accept a relay, but with clear limits. A VFR aircraft flying alongside an IFR aircraft in IMC or near the approach path adds risk: the Cessna is not equipped or cleared for the approach, and the controller cannot separate two aircraft on the basis of a visual relay.
The correct use of the relay is informational only: the Cessna can report whether the B738's landing lights are on, whether the aircraft appears to be descending, and whether the pilot is transmitting on another frequency. It cannot be used to issue clearances, and the controller must not treat the Cessna's report as establishing separation.
The controller should instruct the Cessna to remain clear of the approach path, at a safe altitude and lateral distance, and to report only what it observes. If the Cessna is not able to do this safely, the controller should decline the offer. Meanwhile, the controller should continue to protect the airspace on the assumption that the B738 will complete the published communications-failure procedure, and should coordinate with the tower so that the runway is kept clear.