Blogging the FARs: ATC Light Signals

For the first time, it might be something I need to know.

One of the nice things about my helicopter is that it has two com radios: a standard Bendix King KY196A and the radio that’s part of my Garmin 420 GPS.

My Radio Setup

Bendix King KY196AThe Bendix King is my primary radio and it’s wired into some controls on the cyclic stick. This is a neat feature that’s standard on Robinson helicopters. I can program 9 frequencies into the radio and cycle through them all without reaching down for the radio knobs or buttons. Once I get the frequency I want on standby, I simply push a second button on the cyclic to make that frequency active. I’ve got it programmed for all the CTAF (common traffic advisory frequencies), towers, and ATIS (automatic terminal information service) recordings of the airports I visit most: Wickenburg, Prescott, Deer Valley, etc.

Garmin 420The Garmin is primarily a GPS and I very seldom use the radio. It has the ability to automatically transfer the radio frequency for the current waypoint or selected airport to the standby slot, but when I’m flying, I don’t usually mess around too much with the GPS controls beyond simple Go To and Nearest functions. I prefer having a list of frequencies I need for a flight handy and manually tuning them in. A few times, I used the GPS to look up or check a frequency, but that was usually a practice exercise to make me more proficient with the GPS’s airport directory feature. I subscribe to the data card updates and usually have current (or at least recent) data in there, so it’s pretty reliable. It’s also a lot easier than fumbling with a chart while I’m flying. (One of the drawbacks of flying a helicopter is that you only have one hand to work with while you’re flying; your right hand is pretty much glued to the cyclic.) Another cool thing about the Garmin is that when paired with a Garmin GTX 330 transponder and flying within range of Class B airspace, it can graphically display traffic, as I wrote about here.

A nice thing about having two radios is that I can monitor two frequencies at once. This is especially handy if I want to fly between, say Deer Valley and Scottsdale — a distance of about 9 miles — and want to listen to the Scottsdale ATIS while monitoring the Deer Valley tower for instructions or traffic information. In fact, I’m starting to get into the habit of using the GPS’s radio to monitor ATIS and the Bendix King for two-way communications.

Two Radios are Better than One

Of course, the best thing about having two radios is that if one of them fails, there’s another one there to use. And just recently, having two radios became a very good thing.

On a recent flight, while talking to an airport tower’s controller, I heard static in my headset about halfway through my transmission. Turns out, when the transmission turned to static, it also became garbled on the controller’s end. He couldn’t understand what I was saying. But I could hear him and everyone else just fine.

I immediately tuned in the proper frequency on the Garmin, flicked the right switches to talk on that radio, and retransmitted. No problem. So it wasn’t my push-to-talk switch. It was something in the radio.

I had the radio looked at the same day. Of course, the mechanic could not duplicate the problem. And neither could I on my way home.

Don’t you hate when that happens?

Well, the problem has reared its ugly head several times since then. I’ve had another mechanic and an avionics shop look at it. The mechanic couldn’t duplicate the problem. The avionics shop pulled the radio out for a bench test and could find nothing wrong with it. But they did find a mysterious nut (as in hardware) in the mounting bracket. Once removed, the radio appeared to seat better in the console. We thought the problem would go away. But it didn’t.

So I’m left with a radio that receives perfectly and transmits perfectly about 75% of the time along with a second radio that works fine. I’ve taken to talking on the Garmin and listening to ATIS on the Bendix King.

Unfortunately, no one seems to have a spare KY196A for me to swap temporarily with mine. Putting another radio in there and flying with it for a bit would help me confirm that the problem is the radio and not some kind of helicopter wiring problem. You see, if I put in a different radio and the problem goes away, the problem is definitely my radio. But if the problem persists with a different radio in there, the problem is in the helicopter’s wiring or something related. I tracked down a refurbished KY196A, which I can get for a whopping $2,100. The folks there have promised to take it back if the problem turns out to be in the helicopter rather than the radio. So I’ll be ordering it on Monday.

What All This Has to Do with Light Signals

As usual, I’ve turned a short topic into a long story. But it does explain why light signals are on my mind.

If my second radio also decides to stop transmitting reliably, I may be unable to communicate with a tower. That would not be a good thing if I wanted to land at a towered airport.

The AIM (Aeronautical Information Manual) has a procedure for this. (You can find it in Chapter 6, Section 4-2.) The first thing a pilot who has lost communication capabilities should do is turn his/her transponder to 7600. That sends out a signal that says, “Hey, I’m over here and my radio isn’t working.” If you’re lucky, the tower you’re trying to land out has radar capabilities and can “see” you and this signal. The tower will attempt communication and will react according the results.

In my case, I can hear the tower perfectly fine. I can even transmit a little. So the controller would probably work with that and communications would continue, although rather one-sidedly, with me getting instructions and either clicking my push to talk button or speaking briefly to acknowledge.

But if I couldn’t hear a thing — or couldn’t get the controller to understand that I could hear — the controller would take out the light signal gun and point it at me. And that’s when I’d need to know what the signals meant.

I saw one of these light signal guns close up once, on a visit to Chandler tower. It’s a handheld device that they had attached to the ceiling inside the tower. It can display/flash three different colors of light: red, green, and white. The controller points it at an aircraft having communications problems and either shines a steady light or flashes a light. The pilot is supposed to understand what the signals mean.

So what do they mean?

FAR 91.125: ATC light signals includes this useful table:

Color and type of signal Meaning with respect to aircraft on the surface Meaning with respect to aircraft in flight
Steady green Cleared for takeoff Cleared to land.
Flashing green Cleared to taxi Return for landing (to be followed by steady green at proper time).
Steady red Stop Give way to other aircraft and continue circling.
Flashing red Taxi clear of runway in use Airport unsafe—do not land.
Flashing white Return to starting point on airport Not applicable.
Alternating red and green Exercise extreme caution Exercise extreme caution.

How This Might Appear on a Check Ride

Testing you on your knowledge of this is pretty straightforward for an FAA Examiner. He’ll simply say something like “You discover that your radio doesn’t work as you approach Class Delta airspace. What do you do?”

You reply that you tune your transponder to 7600 and circle outside the airspace until you see a light signal from the tower.

The examiner then says, “Okay, so you see the tower flashing a green light at you. What do you do?”

You explain that the signal means you should “return for landing” or enter the normal traffic pattern.

“You’re cleared to land?” the sly FAA examiner asks innocently.

“No. You need to wait for a steady green before you can land,” you reply, indicating full understanding of FAR 91.125.

To really prepare for this question on a test — and for it happening in real life — it’s a good idea to review the AIM Chapter 4, Section 3-13: Traffic Control Light Signals. Chapter 4, sections 2 and 3 provide additional information for working with Air Traffic Control at an airport. And, if you’re flying IFR (which I don’t), check out Chapter 6, Section 4: Two Way Radio Communications Failure.

Of course, all this might be led up with you explaining what’s required to enter Class D airspace in the first place. But that’s another FAR to explore.

One More Thing

I just remembered that I had a “voluntary radio failure” a while back when returning to non-Towered Wickenburg Airport (E25) from an off-airport location three years ago. If you’re interested, you can read about it here.

What do you think?