What are the lost communications procedures for IFR flight under 14 CFR 91.185?

Under 14 CFR 91.185, if you lose two-way radio communications in IMC, you must continue flying via the route assigned in your last ATC clearance, the route ATC has advised you to expect, or the filed route if no other information exists — in that priority order. For altitude, you must fly the highest of the minimum altitude for IFR operations (MEA, MOCA, MRA, or other applicable minimum IFR altitude), the altitude assigned, or the altitude ATC told you to expect. You then proceed to the destination and begin your approach at the expected further clearance (EFC) time if given, or the estimated time of arrival based on your flight plan.

What's the difference between the route and altitude rules in 91.185 lost comm procedures?

The route rule follows the acronym AVE F — Assigned, Vectored (last assigned heading), Expected, Filed — guiding you through route priority when contact is lost. The altitude rule requires you to fly the highest of the minimum altitude for IFR operations (which may be the MEA, MOCA, MRA, or another applicable minimum IFR altitude, not just MEA), the Expected altitude ATC told you to anticipate, or the last Assigned altitude. These two separate memory aids address different aspects of the lost comms scenario and are both tested on the Instrument Rating Airplane Airman Knowledge Test.

Why does 91.185 tell you to fly the highest of several altitudes rather than just the assigned altitude?

The regulation requires the highest of the minimum altitude for IFR operations (MEA, MOCA, MRA, or other applicable minimum IFR altitude), the assigned altitude, or the expected altitude to ensure obstacle and terrain clearance in the event that ATC had issued a lower altitude for traffic separation purposes that would no longer be safe without active radar monitoring. Flying the highest applicable altitude provides an additional safety margin when controllers can no longer issue traffic or terrain advisories. The PHAK and IFH both emphasize that this rule protects the pilot from transitioning through areas where the assigned altitude alone might not guarantee obstacle clearance.

Lost Communications Procedures in IFR Flight (91.185)

Losing radio communication in instrument meteorological conditions (IMC) is one of the most stress-inducing scenarios an IFR pilot can face. The good news is that the FAA anticipated this emergency and codified a detailed, step-by-step response in 14 CFR 91.185. This regulation tells you exactly which route to fly, which altitude to maintain, and when to begin your approach — leaving almost nothing to guesswork. Mastering 91.185 is not merely an academic exercise for the instrument knowledge test; it is a genuine safety skill that could one day keep you and your passengers alive.

This article walks through the full lost-communications (also called "NORDO" or two-way radio communications failure) procedure from the moment you realize you cannot reach ATC, through the approach and landing at your destination.

First Steps: Confirm the Failure

Before assuming a complete radio failure, 91.185 applies only when two-way radio communication is truly lost. Many apparent failures turn out to be simple fixes: a volume knob turned down, a stuck mic, a wrong frequency, or a headset issue. In the cockpit, quickly check volume, squelch, the frequency selected, your headset and intercom connections, and — if equipped — switch to a backup comm radio or handheld transceiver. Try transmitting on 121.5 MHz (the emergency frequency monitored by ATC facilities, airliners, and military aircraft).

If all attempts fail, you are now operating under 91.185. The regulation distinguishes between two weather scenarios — VMC and IMC — because they change what options are legally available to you.

VMC vs. IMC: Two Different Paths

The first branch in the decision tree is the current weather. If you are in visual meteorological conditions (VMC) at the time of the failure, or if VMC is encountered after the failure, you are expected to continue VFR, land as soon as practicable, and notify ATC as soon as possible. In plain language: if you can see the ground and avoid clouds, you should get down safely under VFR rather than pressing into the IFR system without a radio.

If you are in IMC when the failure occurs — or if you cannot maintain VMC — 91.185 lays out three sets of rules: one for route, one for altitude, and one for leaving a clearance limit and beginning an approach. Each is addressed in turn below.

Which Route to Fly

Under 91.185(c)(1), you fly the route ATC expects you to be flying. The regulation provides a priority order, often remembered by the acronym AVE F:

A — Assigned: Fly the last route that was assigned to you by ATC. If you were told to fly direct to a fix, fly that routing.
V — Vectored: If you were being radar-vectored when communication was lost, fly the route ATC was vectoring you toward (typically the airway or fix that was the apparent destination of the vectors).
E — Expected: If no assigned route fits the situation, fly the route ATC told you to expect (e.g., in the ATIS, a clearance remark, or a "expect direct" advisory).
F — Filed: If you have no assigned or expected route to reference, fly the route you originally filed in your flight plan.

The logic here is that ATC planners use this same priority order to predict where you are. By following it, you remain as predictable as possible, allowing controllers to clear conflicting traffic out of your path.

Which Altitude to Fly

Altitude selection is governed by 91.185(c)(2) and follows its own priority order. The regulation's second altitude option is not strictly the MEA — it is the minimum altitude for IFR operations as published on charts or in altitude information manuals, which may be the MEA, MOCA, MRA, minimum crossing altitude, or another applicable minimum IFR altitude depending on the route segment:

The last assigned altitude — the altitude ATC most recently told you to maintain.
The minimum altitude for IFR operations — for the route segment you are flying (MEA, MOCA, MRA, or other applicable minimum IFR altitude). This ensures terrain and obstruction clearance.
The altitude ATC told you to expect — for example, if the controller said "expect 8,000 in 10 miles," that altitude becomes the expected altitude if you haven't yet received a new assignment.

You fly the highest of these three altitudes. This is a critical exam point: you do not simply fly the last assigned altitude — you compare all three and take the highest, because the expected altitude may be higher than what you were last assigned (perhaps you were climbing to a higher altitude when communication failed). The highest altitude gives you the best obstruction clearance and keeps you predictable to ATC.

For example: you were last assigned 6,000 feet, the MEA for your current segment is 5,200 feet, but ATC told you to expect 8,000 feet in 20 miles. You fly 8,000 feet, because that is the highest of the three.

When to Leave the Clearance Limit and Begin the Approach

This is the section of 91.185 that confuses pilots most, and it is heavily tested. It depends on whether you have been given an expected approach time or an expected further clearance (EFC) time.

When an EFC or Expected Approach Time Has Been Issued

If ATC gave you an EFC time or told you to expect an approach at a specific time, hold at the clearance limit (or the fix from which the approach begins) and leave that fix to begin the approach at the expected time. This is simple and predictable: ATC knows you will start the approach at the time they advertised, so they can sequence traffic accordingly.

When No EFC or Expected Time Has Been Issued

If you reach the clearance limit and no expected time was given, 91.185(c)(3)(ii) prescribes a two-part rule:

If the clearance limit is a fix from which an approach begins, start the approach as soon as possible after arriving at the fix. Do not hold and wait; begin promptly.
If the clearance limit is not a fix from which an approach begins (e.g., you were cleared to a waypoint that is not the initial approach fix), hold at that fix until the ETE (estimated time en route) computed from the flight plan has elapsed, then proceed to the approach fix and begin the approach as soon as possible.

The rationale: ATC can calculate your ETA at the destination based on the flight plan. If they know your filed ETA, they can expect you to begin your approach at approximately that time and can protect the airspace for you.

Transponder and Signals

Throughout a lost-communications situation, squawk 7600 on your transponder. This is the universal lost-communications code. ATC radar facilities monitor for this squawk and will immediately know you have a radio failure. This gives controllers critical information to begin re-sequencing traffic and protecting airspace along your expected route. At towered airports, controllers may also use light gun signals per AIM 4-3-13 to communicate with NORDO aircraft in the vicinity of the airport, so be aware of that possibility as you approach and enter the traffic pattern.

Why These Rules Matter

The IFR system works because ATC can predict where every aircraft will be at any given moment. A radio failure breaks the feedback loop, but 91.185 replaces it with a deterministic set of rules that both the pilot and the controller know. When you follow the regulation precisely, controllers can safely route other traffic around you, protect your approach corridor, and have emergency services standing by if needed. Deviating from 91.185 — even with good intentions — makes you unpredictable and dramatically increases the risk of a mid-air conflict or a controlled flight into terrain.

Key Numbers and Rules

Squawk 7600 immediately upon confirming loss of two-way communications.
121.5 MHz — attempt contact on the emergency frequency before declaring total failure.
Route priority: AVE F — Assigned, Vectored, Expected, Filed.
Altitude: Highest of last assigned, minimum altitude for IFR operations (MEA/MOCA/MRA as applicable), or expected altitude.
Approach timing: At EFC time if given; if not, as soon as possible after reaching the approach fix (or after ETE elapses if the clearance limit is not the approach fix).
VMC encountered after failure: continue VFR, land as soon as practicable.

Memory Aid

For the route, use AVE F (pronounced "ave-eff"): Assigned, Vectored, Expected, Filed. For the altitude, remember the phrase "Highest of the three": last Assigned, Minimum altitude for IFR operations, Expected — some instructors link this to AME (highest). Together, AVE F for route and AME (highest) for altitude give you a compact mental framework you can pull from memory under pressure.

Common Test Traps

"Fly the last assigned altitude" — not always correct. The exam often presents a scenario where the expected altitude is higher than the assigned one. You must fly the highest of the three choices, not simply the last assigned.
Confusing VMC and IMC requirements. If you are in VMC when the failure occurs, you must continue VFR. Many students assume NORDO always means flying the IFR rules of 91.185 — but the regulation explicitly separates the two conditions.
EFC time vs. no EFC time. If an EFC was given, leave at that time. If no EFC was given and the clearance limit is the approach fix, leave immediately upon arrival. Students frequently reverse these or blur them together.
Squawk code confusion. 7600 is lost communications; 7700 is general emergency; 7500 is hijacking. Mixing these up on the test — or in the cockpit — has serious consequences.
"Land as soon as practicable" vs. "land as soon as possible." The VMC lost-comm rule says "practicable" (reasonable given circumstances), not "possible" (immediately). These terms have different operational meanings and the FAA tests the distinction.