What are the emergency squawk codes and when do you use each one?

Squawk 7700 is the general emergency code used when a pilot declares an emergency due to any serious situation such as engine failure, medical emergency, or severe weather encounter. Squawk 7600 is used specifically for two-way radio communication failure (lost comm), signaling ATC that you have lost radio contact. Squawk 7500 is reserved exclusively for hijacking or unlawful interference with the aircraft. As outlined in the AIM, setting the appropriate code alerts ATC radar facilities immediately and triggers a coordinated response.

How do you navigate and land if you experience a two-way radio failure in IMC?

Under 14 CFR 91.185, if you lose radio communications in IMC, you must fly the route assigned in your last ATC clearance, or if being radar vectored, fly directly to the fix, route, or airway specified in the vector clearance. For altitude, you fly the highest of the MEA, the assigned altitude, or the altitude ATC has advised you to expect. For approach, you begin descent from the IAF at the expect-further-clearance time, or if none was given, at the estimated time of arrival based on your filed flight plan.

What's the difference between declaring an emergency and declaring a radio failure to ATC?

Declaring an emergency (squawk 7700) communicates to ATC that there is an immediate threat to the safety of the flight requiring priority assistance, which can include anything from engine trouble to a medical situation. Declaring a radio failure (squawk 7600) specifically tells ATC that you have lost the ability to communicate via radio but the aircraft may otherwise be functioning normally. The distinction matters because ATC and approach control use different procedures for each situation, including issuing light gun signals for radio-failure aircraft operating in VMC near a controlled airport, as described in the AIM.

Emergency Squawk Codes and Radio Failure Procedures

When things go wrong in the cockpit — whether it's a full emergency, a hijacking threat, or a complete radio failure — there is a clear, FAA-standardized system to help ATC know exactly what is happening even without a word being spoken. Transponder squawk codes and radio failure procedures are among the most important emergency tools a pilot can have, and understanding them deeply could one day save your life or the lives of your passengers. These procedures are tested on the FAA Private Pilot Knowledge Exam, but more importantly, they are the kind of knowledge that must be second nature before you ever leave the traffic pattern.

This article walks through every major emergency squawk code, explains what each triggers inside the ATC system, and then dives into the full procedure for handling a two-way radio communication failure — including the specific weather minima and route logic you must follow to get safely on the ground.

The Transponder and How It Works in an Emergency

Your aircraft's transponder responds to radar interrogation signals from ATC ground stations and returns a coded reply that shows your aircraft's position — and, if you have Mode C or ADS-B, your altitude — on the controller's radar display. Under normal operations, ATC assigns you a discrete four-digit squawk code (called a "beacon code") made up of digits 0 through 7. Certain codes, however, are permanently reserved for emergency and special-use conditions. Knowing them is non-negotiable.

The Three Critical Emergency Squawk Codes

7700 — Emergency

Squawk 7700 is the universal distress code. It tells ATC immediately that you are experiencing a serious emergency — engine failure, fire, medical emergency, or any other situation that places the aircraft or its occupants in danger. When a radar controller sees a 7700 return, an alert activates on the scope and the situation is immediately elevated. If you are already talking to ATC and an emergency develops, you can declare verbally on frequency while simultaneously squawking 7700. If you have no time to talk, setting 7700 on the transponder alone still triggers a response. Per the AIM, do not hesitate to use 7700 if you feel the situation genuinely warrants it — there is no penalty for a good-faith emergency declaration, and ATC will render every assistance possible.

7600 — Radio Failure (NORDO)

Squawk 7600 is the radio failure code. "NORDO" is ATC slang for "no radio." Setting this code alerts controllers that you are unable to communicate via radio. It does not mean you are in immediate danger, but it does mean you need special handling — controllers will clear airspace around your expected route and sequence you for landing. The procedures you then follow depend heavily on whether you are in VMC (visual meteorological conditions) or IMC (instrument meteorological conditions) and on what phase of flight you are in. Those procedures are covered in full below.

7500 — Hijacking / Unlawful Interference

Squawk 7500 is reserved for acts of unlawful interference with the flight — most commonly hijacking. Setting 7500 immediately alerts not only ATC but law enforcement and national security agencies. If a controller suspects a 7500 squawk has been set inadvertently, they may discreetly inquire whether the pilot needs assistance. If the pilot responds in a way that confirms the threat is real — or does not respond — emergency protocols at the national level are activated. Never squawk 7500 accidentally or as a test. If you mistakenly select 7500, select a different code immediately and advise ATC of the error.

The Easy Memory Pattern

Memory aid

A simple way to remember the three codes is the rhyme: "7500 — taken over; 7600 — lost radio; 7700 — in danger." You can also remember them in ascending order of immediate threat to the aircraft itself: hijacking (7500) involves human interference, radio failure (7600) is a systems problem, and full emergency (7700) is the broadest life-safety signal. The codes 75, 76, and 77 are also easy to sequence if you remember they start at 7500 and go up by 100.

Two-Way Radio Failure Procedures

A complete radio failure in VMC is more manageable than one in IMC, but both situations have specific regulatory procedures found in 14 CFR §91.185 and the AIM. Let's walk through each scenario methodically.

Radio Failure in VMC (Visual Meteorological Conditions)

If your radio fails and the weather allows you to fly visually, the rule is straightforward: continue VFR and land as soon as practicable. You are not required to land immediately at the nearest airport if a more suitable airport is close by, but you should not continue your original cross-country as though nothing happened. Squawk 7600 the moment you realize communication is lost. Then:

Attempt to re-establish communication on every available frequency, including the emergency frequency 121.5 MHz.
Check that your radio volume, squelch, and headset connections are all functioning. A surprising number of "radio failures" turn out to be a headset jack pulled loose or squelch set too high.
Try transmitting "blind" — that is, broadcasting your position, intentions, and request even if you cannot confirm reception. Controllers may be hearing you even though you cannot hear them.
Land at the nearest suitable airport and notify ATC of the situation.

Radio Failure in IMC (Instrument Meteorological Conditions)

A radio failure in IMC is a more serious event and triggers a detailed regulatory procedure under 14 CFR §91.185. The regulation covers route, altitude, and approach procedures. Remember the acronym AVE F — used widely in training — to recall the priority order for route selection.

Route to fly: The regulation specifies a priority order. Fly the route that ATC has assigned to you. If no assignment exists, fly the route that ATC has advised you to expect. If neither applies, fly the route you have filed in your flight plan. The logic is that ATC will anticipate your route based on this same priority order and will clear the airspace accordingly.

Altitude to fly: For each route segment, fly the highest of the following three altitudes: (1) the last assigned altitude, (2) the minimum IFR altitude (MEA or other applicable minimum for that segment), or (3) the altitude ATC has advised you to expect. Flying the highest of these options ensures obstacle clearance, keeps you in radar coverage when possible, and matches what ATC will anticipate.

Leaving a clearance limit: If you reach a clearance limit (such as a fix or destination airport) and have not yet received a further clearance, the rules are specific. If the fix is the destination airport, begin your descent and approach as close to your expected further clearance time as possible, or if none was given, as close to your estimated time of arrival (ETA) from the filed flight plan as possible. This is critical — ATC will have sequenced other traffic around your anticipated arrival time, so sticking to that schedule keeps everyone safe.

Arriving at a Controlled Airport Without Radio

When you arrive at an airport with an operating control tower while NORDO, look for light gun signals from the tower. ATC controllers keep a light gun ready specifically for this purpose. The light signals you must know are:

Steady green: Cleared to land (in flight) / cleared to taxi (on ground).
Flashing green: Return for landing, to be followed by steady green at the proper time (in flight) / cleared for takeoff (on ground).
Steady red: Give way to other aircraft and continue circling (in flight) / stop (on ground).
Flashing red: Airport unsafe — do not land (in flight) / taxi clear of the landing area (runway) in use (on ground).
Flashing white: Return to starting point on airport (on ground only).
Alternating red and green: Exercise extreme caution (in flight or on ground).

After landing NORDO at a towered airport, squawk 7600 until you have parked. Then notify the tower — in person if necessary — to confirm the situation and debrief ATC so they can clear any holds they placed on traffic for your arrival.

Why These Procedures Matter

Emergency squawk codes work because they are universal and instantaneous. A controller who sees a 7700 on radar knows immediately what to do without waiting for a radio call — and in a real emergency, those seconds matter. Radio failure procedures under 91.185 work because they create a shared expectation: both you and ATC are following the same rulebook, so controllers can predict where you will be and at what altitude, allowing them to protect your route even without two-way communication. The system is elegant precisely because it does not require communication to function.

Key Numbers and Rules

7700 — Emergency (distress). Activates ATC alerts immediately.
7600 — Radio failure (NORDO). Triggers special sequencing and light gun readiness at towers.
7500 — Hijacking / unlawful interference. Escalates to law enforcement and national security agencies.
121.5 MHz — Emergency frequency. Always try this during a radio failure attempt to re-establish contact.
14 CFR §91.185 — The governing regulation for two-way radio communication failure procedures in IFR conditions.
Route priority in IMC: Assigned → Advised → Filed (in that order).
Altitude in IMC: Highest of: last assigned altitude, MEA, or expected altitude.

Common Test Traps

Confusing 7600 and 7700: Test questions often present a scenario and ask which code to squawk. Remember: 7700 is any genuine emergency; 7600 is specifically radio failure without other emergency. If you have a radio failure AND an engine failure, squawk 7700 because the broader emergency takes priority.
"Land immediately" vs. "land as soon as practicable": In VMC with a radio failure, the regulation says "as soon as practicable," not "immediately." This distinction is tested. You use judgment about the most suitable nearby airport.
IMC altitude rule — "highest" not "assigned": Many students think they simply maintain their last assigned altitude. The rule says fly the highest of three options. If the MEA is higher than your assigned altitude, climb to the MEA.
Clearance limit timing: Students confuse "expected further clearance time" with ETA. If ATC gave you an expect-further-clearance time, use that. Only use your filed ETA if no clearance time was given — they are not interchangeable.
Light gun signals in flight vs. on ground: The FAA exam distinguishes between signals given to an aircraft in flight and those given on the ground. Steady green means different things depending on context (cleared to land vs. cleared to taxi). Know both meanings for each signal.