FAR Ninety-One Point One Eight Five, the Squawk Seventy-Six Hundred Procedure, and the Lost Comm Protocol Every IFR Pilot Has to Own Before the Clouds Close In

Two-way radio failure in IMC is uncommon, but it is not rare enough to treat casually. FAR 91.185 gives instrument pilots a complete, step-by-step procedure for handling radio failure - covering route, altitude, timing, and what to squawk. Understanding why the procedure works, not just what to do, is what makes it reliable when workload is high and options are shrinking.

What Should You Do First When Your Radio Goes Silent?

Troubleshoot before declaring a failure. Many incidents pilots describe as radio failures turn out to be something else entirely.

Work through this sequence: check your headset connection at the jack, check the volume and squelch on the audio panel, confirm you are on the correct frequency, and verify you have not accidentally selected a dead comm. Try your number two comm radio. Transmit on guard frequency (121.5 MHz). If you have a handheld radio in your flight bag, retrieve it.

ATC is also trying to reach you. Controllers will call on your last assigned frequency, on guard, on previous frequencies, and on frequencies associated with nearby navaids. They have dealt with this before. You have a meaningful window to troubleshoot before the situation becomes critical.

What Transponder Code Do You Set for Radio Failure?

Once you have confirmed the radio is genuinely not working, set your transponder to squawk 7600. This is the code for two-way radio communications failure.

Do not confuse it with 7700 (general emergency) or 7500 (hijacking). Set 7600 and leave it there for the remainder of the flight.

When radar facilities see that squawk, they know what is happening. Controllers will adjust traffic flow around your projected position and attempt to keep other aircraft clear of your route. They are operating on an assumption - that you know the procedure and are executing it correctly. Your job is to make that assumption true.

What Are the Lost Comm Rules for VFR Flight?

Under VFR, FAR 91.185 is straightforward: continue VFR and land as soon as practicable. That word matters. Practicable does not mean convenient - it means the nearest suitable airport as soon as you can reasonably get there.

If reaching that airport requires entering Class D or Class C controlled airspace, watch for light gun signals from the control tower. The tower will sequence you if they can see you. Do not delay. The regulation’s intent is clear: get on the ground promptly.

How Do You Choose Your Route Under IFR Lost Comm? (AVEF)

Route selection follows the mnemonic AVEF - in priority order:

• A - Assigned: the last routing clearance ATC actually issued. Fly it exactly.
• V - Vectored: if you were being actively vectored when the failure occurred, continue those vectors until you reach a published route or fix.
• E - Expected: if ATC told you to anticipate a specific routing or clearance that you had not yet received, that expectation now guides your route.
• F - Filed: if none of the above apply, revert to your original filed flight plan route.

In most real-world scenarios, the answer is Assigned - you were given a clearance, and you continue flying it. The governing principle is predictability. A controller is still tracking your radar return and needs to know exactly where you are going. Do not improvise a more efficient routing. Fly precisely what you were cleared to fly.

What Altitude Do You Fly During IFR Lost Comm?

Fly the highest of these three values:

1. The Minimum Enroute Altitude (MEA) for your current route segment
2. The altitude ATC told you to expect
3. The altitude from your last ATC assignment

Highest - not lowest.

Here is a concrete example. You were assigned 8,000 feet. The MEA on your airway is 6,000 feet. ATC told you to expect 10,000 feet in approximately 20 miles, but you lost comms before that clearance arrived. Fly 8,000 feet until you reach the 20-mile point, then climb to 10,000 feet, because 10,000 is the highest of the three applicable values at that point.

The reasoning matters. When ATC can no longer communicate with you, they make a calculated assumption about your altitude. If they sequence traffic around the assumption you are at 10,000 feet and you are actually sitting at 8,000, you may be in direct conflict with aircraft they cleared below your expected position. The altitude rule creates a predictable, conservative ceiling that keeps the separation system intact.

Why Does Timing Matter in Lost Comm Procedures?

Timing is consistently underestimated in checkride preparation, and it is just as critical as route and altitude.

When you reach your destination, do not begin the approach the moment you hit the initial approach fix. FAR 91.185 requires you to begin the approach as close as possible to your Expected Further Clearance (EFC) time if ATC assigned one. If no EFC time was given, use the Estimated Time of Arrival (ETA) from your filed flight plan or the last estimate ATC provided.

ATC is watching your transponder return and building a traffic picture around your expected arrival time. Appearing 25 minutes early and descending out of your assigned altitude puts you in potential conflict with aircraft sequenced ahead of you based on your filed ETA. The timing is not administrative - it is what keeps you separated from traffic you cannot see or talk to.

What Happens at a Clearance Limit?

If your routing brings you to a fix where you were told to hold pending further clearance, you hold there.

• If you have an EFC time, hold until that time, then depart toward the destination.
• If you were never given an EFC time, depart the clearance limit fix at your filed Estimated Time of Arrival for that point.

The principle is identical to everything else in this procedure: remain on the timeline. ATC can protect a predictable aircraft following published procedures. An aircraft making ad-hoc route or timing decisions cannot be safely sequenced.

How Do You Fly the Approach Under Lost Comm?

When your EFC time or estimated arrival time arrives, fly the approach exactly as published to your authorized minimums.

If you break out and can land, land. If you do not break out, execute the missed approach as published and proceed to your filed alternate. Your alternate requirements do not disappear because your radio failed. If your destination is below minimums and you lack the fuel to reach the alternate, the lost comm procedure cannot resolve that - it is a pre-departure planning failure.

When Does Lost Comm Become a Full Emergency?

FAR 91.185 is written for a radio failure in otherwise manageable conditions. If the failure occurs alongside other serious problems - critically low fuel, weather at the destination well below forecast - you are no longer dealing only with a lost comm. You are dealing with an emergency.

In that case, declare the emergency on any available frequency including guard (121.5 MHz), and squawk 7700 to signal a full emergency rather than a communications-only failure. Use the tools that fit the actual situation.

What Is the Examiner Looking for on the Instrument Checkride?

The Airman Certification Standards for the instrument rating explicitly list lost communications procedures as testable knowledge, in both the oral and the flight portions.

Examiners check for these specifically:

• Do you troubleshoot before declaring a failure?
• Do you squawk 7600 without being prompted?
• Can you apply AVEF logic to a specific scenario?
• Can you explain why you fly the highest of the three altitudes, not just which one?
• Do you understand timing and what to do at a clearance limit?

The most common failure point is knowing the mnemonic without understanding the concept. When an examiner constructs a specific scenario and asks which altitude you would fly and why, a pilot who memorized letters but not reasoning cannot answer. The edge cases answer themselves when you understand why the procedure works.

Practical Tip: Carry a Charged Handheld Radio

Fly with a tested, charged handheld transceiver in your flight bag - not because the regulation requires it, but because it converts a genuine IFR emergency into a manageable inconvenience. Practice with it on the ground before you need it in the air. Fumbling with unfamiliar controls in actual IMC is not the moment to locate the squelch button.

Key Takeaways

• Troubleshoot first. Most “radio failures” are headset jacks, wrong frequencies, or audio panel settings.
• Squawk 7600 immediately upon confirming genuine two-way communications failure - not 7700, not any other code.
• AVEF determines your IFR route in priority order: Assigned, Vectored, Expected, Filed.
• Fly the highest of MEA, expected altitude, or assigned altitude - this keeps your position predictable for ATC.
• Timing is not optional. Begin the approach at your EFC time or filed ETA. Arriving early disrupts sequencing for traffic you cannot see.