Transmitter failure on a night ILS into Class D
A twin-jet business aircraft is inbound IFR at night to an aerodrome in Class D airspace. The last ATC transmission received is: 'X-ray Bravo, turn right heading 240, maintain 3,000 ft until established on the localizer, cleared ILS runway 27 approach, squawk 6043.' The crew read back, and from that point can hear ATC perfectly but cannot transmit on either VHF set; a relay attempt through the company frequency fails. Weather is IMC with a ceiling of 400 ft and visibility 2,000 m; the ILS decision altitude is 250 ft. Fuel remaining is 1 h 20 min. The crew have not selected 7600. The aerodrome is due to be reclassified as Class C airspace from the next AIRAC cycle, and the tower controller can see the aircraft on radar but has had no response to three calls.
1. What should the crew do now under the radio-communication failure procedure?
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Apply the communications failure procedure of SERA.8035 (ICAO Annex 2, 3.6.5).
- Select code 7600 immediately. The crew's failure to do so is the first error to correct: 7600 is what tells the controller that the silent aircraft is a radio-failure case and not an emergency or a mistake. It replaces the assigned 6043.
- Try to restore communication: the second VHF set, 121.5 MHz, a relay through another aircraft, CPDLC or ACARS if fitted, and company operations by satellite or telephone to pass the message to ATC.
- Fly the last clearance received. 'Turn right heading 240, maintain 3,000 ft until established on the localizer, cleared ILS runway 27' remains the plan: the aircraft is cleared for the approach and must not descend below 3,000 ft except on the localizer/glideslope.
- With the weather IMC at 400 ft ceiling, the VMC option - continue in VMC, land at the nearest suitable aerodrome and report arrival - is not available. In IMC the procedure is to maintain the last assigned speed and level, or minimum flight altitude if higher, for the prescribed period after the failure, then adjust to the flight plan, descend at or near the expected approach time, and complete an instrument approach within the prescribed time of the ETA. In practice on a radar-vectored arrival this means establishing on the localizer at 3,000 ft as cleared, then flying the ILS.
- Keep a listening watch on 121.5 MHz and the tower frequency, and watch for light signals from the tower on final, because the tower may use them.
If fuel becomes critical or the approach cannot be completed safely, declare an emergency on 121.5 MHz with MAYDAY and act accordingly. A radio failure does not require the crew to press on into an unsafe situation.
2. The tower cannot raise the aircraft and decides to use light signals. State the meanings the crew must know for an aircraft in flight and after landing.
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Aerodrome control may signal to an aircraft that cannot be reached by radio, and the signals have the same force as a clearance. The crew must keep a continuous watch for them.
To an aircraft in flight (Annex 2, Appendix 1):
- Steady green: cleared to land.
- Steady red: give way to other aircraft and continue circling.
- Flashing red: the aerodrome is unsafe; do not land for the time being.
- Flashing green: return for landing, to be followed by a steady green at the proper time.
- Red pyrotechnic signal: notwithstanding any previous instructions, do not land for the time being.
To an aircraft on the ground:
- Steady green: cleared to take off.
- Steady red: stop.
- Flashing green: cleared to taxi.
- Flashing red: taxi clear of the landing area in use.
- Flashing white: return to the starting point on the aerodrome.
Practical consequences: a steady green on final is an authorisation to land, so the crew may complete the approach; a red signal must be obeyed even though the aircraft is established and low on fuel. After landing the aircraft should be brought to a stop rather than taxied off the runway on assumptions, and the crew should expect to be marshalled, since taxiing without a clearance is not permitted. All light signal instructions and responses should be recorded and reported after landing.
3. If the same event occurred after the aerodrome became Class C, what would change for this crew and for the controller?
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The crew's radio-failure procedure and the light-signal meanings do not change with the airspace class: they come from the rules of the air, not from the classification. What changes is the service and the separation that the controller owes.
- In Class D, IFR flights are separated from other IFR flights and receive traffic information about VFR flights (and VFR flights receive traffic information about IFR flights), but IFR is not separated from VFR. The controller protecting a silent IFR aircraft must therefore rely on traffic information and on keeping the runway clear.
- In Class C, IFR flights are separated from IFR flights and from VFR flights, and VFR flights are separated from IFR flights while receiving traffic information about other VFR flights. The silent aircraft on the ILS would in future have a protected block of airspace against VFR traffic, and the controller would not clear VFR traffic into conflict with it.
- Clearance requirements remain: VFR flights need an ATC clearance in both classes, and both classes require continuous two-way radio and, where prescribed, an SSR transponder.
The VMC minima themselves are set by altitude band under SERA.5005, not by the airspace class, so reclassification does not relax them: it does not make 2,000 m visibility and a 400 ft ceiling legal for VFR. For the crew, the operational answer is unchanged - select 7600, fly the last clearance, watch for light signals, and declare an emergency if fuel or safety requires it.