Radio Communication Failure

What "radio communication failure" means

Radio communication failure (RCF) is the situation where pilot and controller can no longer talk via radio. It can be:

• Total — radio broken, antenna damaged, power lost
• Partial — transmitter works but not receiver (or vice versa)
• Apparent — wrong frequency, low volume, squelch closed too tight

The golden rule: before declaring RCF, rule out trivial causes. 80% of "radio failures" are actually:

• Volume too low (happens more than you'd think)
• Squelch too tight cutting weak signal
• Wrong frequency (set 119.000 instead of 119.450)
• Stuck PTT or disconnected headset
• Frequency change not confirmed (still on previous one)

Step-by-step procedure if you suspect RCF

When you fear loss of communications, follow this sequence:

1. Verify settings

• Audio volume above 50%
• Squelch in automatic or middle position
• Correct frequency (check AIP, ATIS, or pre-flight briefing)
• Headset connected in both jacks
• Boom mic in position

2. Try a "frequency check"

"Lugano Tower, HB-PMR, radio check on 119.000."

If you get a response, you were just distracted. If you get nothing, try the next step.

3. Listen on 121.500 MHz

The international emergency frequency 121.500 MHz is monitored by all towers and many aircraft. If you hear normal chatter, your radio works — the problem is the previous frequency. If you hear nothing here either, the radio is probably broken.

4. Squawk 7600

Set the transponder to 7600, the ICAO code for radio communication failure. All area radars will see it and understand your situation. Skyguide will activate the RCF procedure on their side.

5. Blind transmission

Even if you receive nothing, continue to transmit "blind" at every significant change. Standard structure:

"[Station], [callsign], transmitting blind, [position], [intentions], possible radio failure."

Example: "Lugano Tower, HB-PMR, transmitting blind due to radio failure, position 5 miles south, two thousand five hundred feet, intending to land Lugano runway 19."

If your transmitter works (but not receiver), the controller hears you perfectly and can respond — even if you don't hear them. That's why light signals exist.

Tower light signals

Every control tower has a signal lamp (signal lamp / Aldis lamp) that sends colored light at a single aircraft. It's a "20th-century" procedure still required by ICAO and practiced regularly:

Signal	Aircraft in flight	Aircraft on ground
Steady green	Cleared to land	Cleared for take-off
Flashing green	Return for landing (clearance to follow)	Cleared to taxi
Steady red	Give way to other aircraft, continue circling	Stop
Flashing red	Aerodrome unsafe, do not land	Vacate landing area in use
Flashing white	Land at this airport and proceed to apron	Return to starting point
Red flare	(anywhere) Notwithstanding any previous instructions, do not land for the time being	—

RCF re-entry procedure in controlled airspace

If you're in CTR or TMA with RCF, the standard ICAO procedure is:

1. Squawk 7600
2. Continue flight per last received clearance
3. Watch for tower light signals (overflying the field at 1500 ft AGL and observing)
4. Land when you receive steady green, vacating the runway as quickly as possible after landing

If you're VFR outside controlled airspace, land at the nearest suitable airfield and contact ATC from the ground (phone or mobile).

What NOT to do in case of RCF

• Don't panic. The aircraft flies even without radio.
• Don't head home on your own initiative if you're near destination and have a valid clearance.
• Don't change altitudes or headings without reason. Maintain last clearance.
• Don't turn off the transponder. Even broken, it's your way of communicating with radar.
• Don't forget the phone. A call to the tower number after landing closes the RCF procedure correctly.

Swiss specifics

Summary — to remember

1. Check trivial causes first: volume, frequency, headset, squelch.
2. Squawk 7600 as soon as you confirm RCF.
3. Transmit blind assuming your transmitter works.
4. Know the light signals by heart.
5. Maintain last valid clearance until new instructions are received.
6. 121.500 MHz always as secondary frequency.
7. Phone the tower after landing to close the procedure correctly.

Sources

• ICAO Annex 2 — Rules of the Air, Section 3.6.5 (Radio communication failure)
• ICAO Doc 4444 — PANS-ATM, Chapter 15.3
• ICAO Doc 9432 — Manual of Radiotelephony, Chapter 6
• AIP Switzerland — ENR 1.1.5 (Radio communication failure procedures)