Two-Way Radio Communications Failure (Lost Comm IFR)

6.communications-failure-procedures. Two-Way Radio Communications Failure (Lost Comm IFR)

A two-way radio communications failure in instrument meteorological conditions (IMC) is one of the few situations in which a pilot may legally deviate from an ATC clearance without a prior amendment. The governing regulation is 14 CFR 91.185, which prescribes specific routes, altitudes, and timing the pilot must fly when communication with ATC is lost. Compliance with these rules allows ATC to predict the aircraft's position and protect the airspace ahead of it.

Initial Actions

Upon recognizing a communications failure, the pilot should first attempt to restore communication. Standard troubleshooting includes:

• Check volume, squelch, headset jacks, and the audio panel selector.
• Verify the correct frequency and try the previously assigned frequency.
• Try alternate frequencies: 121.5 MHz (guard), an FSS frequency, ATIS for an attended airport, or a nearby Center/Approach frequency.
• Attempt contact through another aircraft as a relay.
• Use the transponder to alert ATC: squawk 7600 for radio failure (and 7700 for an emergency if the situation warrants).
• Receivers may still work — listen for ATC transmissions and acknowledge by ident or by complying with instructions.

VFR Conditions (91.185(b))

If the failure occurs in VMC, or VMC is encountered after the failure, the pilot must continue the flight under VFR and land as soon as practicable. "As soon as practicable" does not mean the nearest airport — the pilot may consider suitability, weather, and convenience, but should not continue IFR in VMC indefinitely.

IFR Conditions (91.185(c))

If VMC cannot be maintained, the pilot must continue the flight according to the rules below. Memorize these with the mnemonics AVE F (route) and MEA (altitude).

Route — fly, in this order of priority:

• Assigned in the last ATC clearance received;
• If being Vectored, the direct route from the point of radio failure to the fix, route, or airway specified in the vector clearance;
• The route ATC has advised may be Expected in a further clearance;
• In the absence of any of the above, the route Filed in the flight plan.

Altitude — for each route segment, fly the highest of:

• The altitude or flight level Assigned in the last ATC clearance;
• The Minimum altitude (including MEA) for IFR operations on that segment;
• The altitude or flight level ATC has advised may be Expected in a further clearance.

The "highest of" rule is applied segment by segment, not as a single altitude for the entire route. If a higher MEA exists on a subsequent segment, climb to it when reaching that segment; otherwise, maintain the appropriate altitude until reaching the point where a change is required.

Leaving the Clearance Limit (91.185(c)(3))

The clearance limit is the fix to which the aircraft has been cleared. Two cases:

1. Clearance limit is a fix from which the approach begins (an IAF): Begin descent or descent and approach as close as possible to the expect-further-clearance (EFC) time. If no EFC time was received, begin descent or descent and approach as close as possible to the estimated time of arrival (ETA) calculated from the filed or amended estimated time en route.

2. Clearance limit is not a fix from which the approach begins: Leave the clearance limit at the EFC time. If no EFC was received, leave the clearance limit upon arrival, proceed to a fix from which the approach begins, and commence the approach as close as possible to the filed/amended ETA.

Example

Cleared from KAPA to KGJT via V8, climb and maintain 12,000, expect 16,000 ten minutes after departure. Comms fail at 11,000 prior to reaching the expect altitude. The pilot would continue on V8 (assigned route), climb to 16,000 ten minutes after departure (highest of assigned, MEA, expected — applied per segment), and arrive at KGJT to begin the approach as close as possible to the filed ETA, adjusting for any holding or vectors received.

Practical Considerations

While 91.185 dictates the legal procedure, the regulation also recognizes pilot-in-command authority under 91.3(b) to deviate as required to meet an emergency. ATC will treat a 7600 squawk as a presumed lost-comm and protect altitudes and routes consistent with 91.185. Controllers will broadcast instructions in the blind on the last assigned frequency and on appropriate NAVAID voice features ("transmitting in the blind"); pilots whose receivers are working should monitor and comply.

In VMC, pilots may receive a light-gun signal from the tower at the destination. Review the meanings: steady green (cleared to land), flashing green (cleared to taxi/return for landing in flight), steady red (give way/stop), flashing red (airport unsafe/taxi clear of runway), flashing white (return to starting point on airport), alternating red/green (exercise extreme caution).