§ 91.185 IFR operations: Two-way radio communications failure.

Section 91.185 — IFR operations: Two-way radio communications failure — is the famous 'lost comms' rule. It is one of the most-tested IFR regulations.

Paragraph (a) — General: Each pilot who has two-way radio comms failure when operating under IFR must comply with this rule UNLESS the pilot determines that another procedure is safer.

The two big questions: WHAT to do, and WHEN to descend.

Paragraph (b) — VFR conditions: If radio comms fail in VFR conditions or if the pilot encounters VFR conditions after the failure, the pilot SHALL continue VFR and land as soon as practicable.

Paragraph (c) — IFR conditions: ROUTE rule (AVE-F): The pilot must fly the route in this priority:

• Assigned — by the last ATC clearance received
• Vectored — direct from the point of the failure to the fix, route, or airway specified in the vector clearance
• Expected — by the route ATC has advised may be expected in a further clearance
• Filed — by the route filed in the flight plan

Paragraph (c)(2) — ALTITUDE rule (MEA, the higher of):

• The altitude or flight level assigned in the last ATC clearance received; OR
• The minimum altitude (MEA, MOCA, etc.) for IFR operations on that route segment; OR
• The altitude or flight level that ATC has advised may be expected in a further clearance

Paragraph (c)(3) — Leaving the clearance limit: Two cases:

• (i) When the clearance limit is a FIX from which an approach BEGINS: commence descent and approach as close as possible to the EFC time (if received) or the ETA computed from the filed flight plan (if no EFC).
• (ii) When the clearance limit is NOT a fix from which an approach begins: leave the clearance limit at the EFC time (if received) or upon arrival over the clearance limit (if no EFC), and proceed to a fix from which an approach begins and commence descent/approach as close as possible to the ETA.

Squawk 7600: Squawking 7600 alerts ATC to the radio failure. Many radar facilities automatically transmit to the aircraft on the previously-used frequency when 7600 is detected.

Reference: AIM 6-4 on Two-Way Radio Comms Failure; FAA-H-8083-16 Chapter 8.

AVE-F and the Altitude Hierarchy — How § 91.185 Tells You to Fly Lost Comm

Lost comm in IMC sounds catastrophic until you realize the FAA has written the script for you. § 91.185 isn't a suggestion — it's a contract between you and ATC. They assume you're flying it. You assume they're keeping the airspace clear. The trick is knowing the script cold before the radios quit, because this is no time to be flipping pages.

Step one lives in paragraph (b): if you lose comms and you're in VMC — or you encounter VMC at any point afterward — you continue VFR and land as soon as practicable. That word "encounter" matters. If you punch out of the clouds 40 miles from your destination, you're done with the IFR script. Land. Period. This exception trumps everything else in the rule.

If you're stuck in IMC, paragraph (c) takes over with two questions: What route do I fly? and What altitude do I hold?

The route hierarchy is taught as AVE-F, straight from § 91.185(c)(1):

Then paragraph (c)(2) handles altitude — and this one trips students. You don't pick one altitude. You fly the highest of these three, for each route segment: the Assigned altitude in your last clearance, the Minimum En Route Altitude (MEA) for that segment, or the altitude ATC told you to Expect. Some instructors teach this as "MEA is the floor" — fine, but don't forget the "Expected" piece. If a controller said "expect 10,000 in one zero minutes," you owe them that climb at the ten-minute mark even after the radios die. That's the part students miss when nobody said the magic word.

What an Examiner Asks About § 91.185

This regulation shows up on every instrument oral. Examiners aren't looking for a recitation — they want to see you walk the decision tree without freezing. Be ready for these:

• "What do you do first if you lose comms IFR?" — Troubleshoot the radio (volume, frequency, headset, mic, audio panel), squawk 7600, then apply § 91.185.
• "What's the route priority?" — AVE-F: Assigned, Vectored, Expected, Filed — paragraph (c)(1).
• "What altitude do you fly?" — The highest of Assigned, MEA, or Expected for each segment — paragraph (c)(2). Not the average. Not the last one given. The highest.
• "If you reach your clearance limit, when do you leave it?" — At your EFC time. If no EFC was issued, leave to begin the approach so as to arrive as close as possible to your filed ETA.
• The trick question: "What if you break out of the clouds halfway there?" — Paragraph (b) wins. VMC trumps the whole IFR script. Continue VFR, land as soon as practicable.

Squawk 7600 — A Real Lost Comm, Under § 91.185

Picture it: you're cruising at 8,000 in solid IMC, 60 miles from destination, cleared via your filed route, last instruction was "expect the ILS 16 approach, maintain 8,000, expect 5,000 in one zero minutes." You key the mic to check in with the next controller and — nothing. Dead silence. No sidetone. The radios are gone.

Here's how you fly the script:

1. Troubleshoot first. Check volume, squelch, audio panel selectors, headset jacks, mic button. Try the standby radio. Try guard (121.5).
2. Squawk 7600. Now ATC knows. The moment that code hits the scope, controllers start clearing airspace along your expected route and altitude.
3. Run AVE-F. You were on your assigned route, so keep flying it (Assigned wins). At the ten-minute mark from your last clearance, climb or descend to your Expected altitude if higher than MEA. In this case, 5,000 is below 8,000, so you hold 8,000 until reaching a segment where 5,000 becomes appropriate per (c)(2).
4. Arrive at the clearance limit. If your clearance limit is a fix from which the approach begins, commence the approach at your EFC, or — if none was issued — as close as possible to your filed ETA. If it's not an approach fix, leave at EFC and proceed to a fix from which the approach begins.
5. Fly the approach. Land. Call ATC by phone after you're tied down.

Here's the part new instrument pilots underestimate: ATC is flying the same rulebook you are. They assume you're following § 91.185 to the letter, and they protect the airspace accordingly. The worst thing you can do is improvise — go off-script and the airspace they're holding for you is empty, while the airspace you've wandered into isn't. Fly the script. The script works.