Radio failure on a VFR flight: squawk 7600 and the light-gun signals

Somewhere in every flying life is a cockpit that goes quiet. You are on downwind at a towered field, you key the mic to report your position, and what comes back is your own voice through the cabin and nothing else — no readback, no traffic, no tower. You try the second radio. You check the volume, the squelch, the frequency, the headset jack. Still nothing. The runway is off your left shoulder, the tower is a mile ahead, and the one tool you were counting on to get permission to land just went dark in your hand.

This is a moment the PSTAR is quietly preparing you for, and it is smaller than it feels. A lost radio in good weather is a nuisance, not a crisis — the airplane flies exactly as well as it did a minute ago, and you can still see the runway. What changes is only how you and the tower talk. There is a drill for that, and it is two moves: tell the system your radio is dead, then read what the tower shows you back. We will take them in the order you would fly them.

First move: squawk 7600

The fastest way to tell everyone on the ground that your radio has failed is not a radio call — you no longer have one of those. It is your transponder. Reach down and set code 7600. That is the code that exists for exactly this: communication failure. It lights up an alarm on the controller's display and flags your aircraft as the one that has lost comms, so the tower stops waiting for a call that is never coming and starts talking to you the other way.^[3]

7600 sits between its two neighbours in the emergency block, and the exam wants you to keep them straight. 7700 is the general emergency code; 7500 is unlawful interference — a hijack — and you never select it to mean anything else.^[3] All three begin with a seven, which is why the guidance is to change codes deliberately — dial carelessly and you can flash an emergency code you never meant, telling the ground the wrong story for a moment. Set the digits with intent.^[3]

There is a regulation under the reflex, and it is worth knowing because the wording is precise. For a VFR flight that loses two-way radio while operating in Class B, C, or D airspace, the pilot must do three things: leave the airspace — and where that airspace is a control zone, you leave it by landing at the aerodrome the control zone is built around; set the transponder to 7600 if you are equipped; and inform an air traffic control unit as soon as possible of what you did.^[4] Read that carefully. The rule does not send you home or off to a quiet field. Inside a control zone it sends you in — you are expected to come back and land at the towered airport whose zone you are already in, not to slink away from it.

Which is why the second move matters, because the tower has to be able to clear you in without a radio. And it can.

The tower can clear you by light

Here is the part students are surprised by: getting a clearance by radio was never the only legal way. At a controlled aerodrome the regulation requires you to obtain clearance to taxi, take off, or land from the tower either by radio communication or by visual signal.^[5] The light gun is not something the controller improvises when the radios fail. It is the other half of a rule you were already flying under — a signalling lamp in the tower cab that throws a tight coloured beam at your aircraft, and each colour and cadence is a specific instruction.^[2]

The whole set turns on two questions: what colour, and steady or flashing. And every signal means one thing to an aircraft in flight and a different thing to an aircraft on the ground — that split is the entire game, and it is exactly where the PSTAR lays its traps.^[1]

Here is the full set the tower can show you:

• Steady green — in flight: cleared to land. On the ground: cleared for take-off.^[1]
• Flashing green — in flight: return for landing (you are not cleared to land yet). On the ground: cleared to taxi.^[1]
• Steady red — in flight: give way to other aircraft and keep circling. On the ground: stop.^[1]
• Flashing red — in flight: airport unsafe, do not land. On the ground: taxi clear of the landing area in use.^[1]
• Flashing white — a ground signal only: return to your starting point on the airport.^[1]

Six lines to memorise, and a pattern that carries most of the weight. Steady is a command that stands; flashing is a redirection — something has to change. Steady green is the clearance itself; steady red parks you where you are, circling or stopped. Every flashing signal wants a change of plan: come back around, taxi, clear the landing area, go back where you started. Layer the colour on top — green is permission, red is denial, white is go home — and you can rebuild the whole table from the logic instead of the rote.

The two greens are where marks go to die

The bank does not test these signals gently, and the greens are its favourite trap. Both green stems read almost identically, and the exam sets them side by side so your optimism can pick the wrong one. Here they are, verbatim from Transport Canada's own study guide:

A steady green light directed at an aircraft means respectively in flight on the ground

— keyed answer: cleared to land; cleared for take-off.^[1]

A series of green flashes directed at an aircraft means respectively in flight on the ground

— keyed answer: return for landing; cleared to taxi.^[1]

The trap is the airborne meaning of the flashing green. It is not "cleared to land" — that is the steady green — it is "return for landing," which means come back around and set up again; you have not been cleared for anything yet. On a radio-out approach, mistaking a flashing green for a landing clearance is how you continue to a runway the tower was trying to wave you off of. And the same flashing green on the ground means something entirely different again — cleared to taxi. One signal, two meanings, and the exam pays out on the seam between them.

Tell the tower you understood

Reading the light is only half of it. The controller cannot hear you say "roger," so you answer with the airplane. The regulations spell out how to acknowledge a visual signal, and it depends on where you are.

By day, you acknowledge with full movement of the rudder or the ailerons — whichever the tower can see most easily — repeated at least three times, or simply by taxiing the aircraft to the position you have been cleared to.^[2] In the air that full aileron movement reads as rocking the wings; on the ground, as working the controls through their travel where the cab can see it. None of it is subtle, and it is not meant to be: the point is a signal the controller can read from the cab with the naked eye, closing the loop the radio would normally close.

What the PSTAR is really testing

The light-gun table is pure PSTAR: the Visual Signals questions run the tower-light meanings as in-flight-versus-on-ground pairs, exactly as you just read them.^[1] The squawk itself sits a step to the side of the exam — the PSTAR's transponder questions ask about the everyday VFR codes, not the failure code — but the regulation behind 7600, the one that sends a radio-out VFR flight back to land in its own control zone, is exactly the kind of rule the exam is built on.^[4] The section is small, it is pure recall, and it is entirely learnable, which is precisely why losing marks here stings: nobody derives a light-gun table under pressure on the exam, and nobody should be reading one for the first time with a dead radio and a runway ahead. You learn it once, cold, so both times it counts — on the paper and in the seat — the meaning is already in the airplane with you.

If a signal ever genuinely stumps you aloft with no radio to ask, the conservative reading is the safe one: treat a red as do not, keep the airplane flying, keep circling clear of other traffic, and wait for the tower's next signal rather than force an approach. See-and-avoid never transferred to the controller just because your radio quit.^[5]

A dead radio near a control tower is one of the more theatrical things that can happen to a student pilot and one of the least dangerous, provided the drill is already yours. Squawk 7600, fly the airplane, and read the light the way you read a page you have read a hundred times. The PSTAR asks the question on paper first so that the day it asks it for real, you already know your lines — and the only thing left to do is fly them.