Transponders for Dummies

Get the facts straight.

One of the podcasts I listen to on my morning walk is called Stuff You Should Know. Produced by the folks responsible for the How Stuff Works website, Stuff You Should Know is a pretty thorough discussion of a specific topic by two hosts, Josh and Chuck, who base their discussion on a website article and some of their own research. It’s a great way to learn new things when you’re stuck doing something mindless — like walking, driving, flying, etc. So far, I’ve learned about revenge, diamonds, Atlantis, social security numbers, air traffic control (ATC), and bullfighting. You can find its RSS feed here.

The April 24, 2012 episode of the podcast was titled “How Air Traffic Control Works.” It was based on a How Stuff Works article of the same name by Dr. Craig Freudenrich. The article was very detailed; the podcast was based on that article and several other articles on How Stuff Works.

As a pilot, I know quite a bit about air traffic control — but not everything. The article (and podcast) was mostly concerned with ATC as it relates to airliners. After all, that’s how most people interact with aviation. But I’m involved with general aviation (as opposed to airline aviation or military aviation). And, as a helicopter pilot, I don’t interact with ATC nearly as much as, say, an instrument rated pilot flying a King Air from Phoenix to Seattle.

So I was hoping that I could learn something new. And I did.

But I also heard the podcasters misinforming listeners about transponders (among a few other things). And if there’s one thing I hate, it’s when an informational article or podcast or video — or anything else — includes errors. So I thought I’d set things straight.

What Is a Transponder?

Garmin Transponder
This is the Garmin 330 Transponder I have in my helicopter.

A transponder is a part of an aircraft’s avionics. It assists air traffic control by making it easier for ATC radar to “see” an aircraft. It basically sends out a signal that says “Here I am!” ATC radar can pick up this signal, along with any additional information encoded within it, to plot the aircraft as a “blip” on the radar display and differentiate it from other aircraft.

Transponders include a feature that enables the pilot to send a specific “squawk” code. Normally, in VFR (visual flight rules) flight, an aircraft’s transponder is set to send the code 1200 — in fact, this code is used so often that many transponder models — including mine — have a VFR button the pilot can press to quickly enter that code.

IFR (instrument flight rules) flights are assigned a discreet discrete squawk code. This code is used by ATC to identify that particular aircraft. Sometimes, when operating within tower-controlled airspace, ATC will assign a discreet discrete code to a VFR flight. Or perhaps a specific code is used by signatories to a letter of agreement between ATC and pilots — for example, 0400 is used by Sharp Alpha signatories in the Phoenix class bravo airspace.

Most transponders are equipped with automatic altitude reporting features, which is known as Mode C. Indeed, Mode C transponders are required within 30 miles of a class Bravo airport — think major airports like the kinds most airlines serve — and in a bunch of other places detailed in Part 4-1-20 of the Aeronautical Information Manual (AIM), “Transponder Operation.” (This, by the way, is an excellent resource for learning more about transponders in general.) Mode C transponders interface with an aircraft’s altimeter to get the altitude of the aircraft and send that information to ATC.

Garmin 420 GPS
My Mode S transponder interfaces with my Garmin 420 GPS to show traffic when information is available. I blogged about this here.

A Mode S transponder, which is what I have on my helicopter, is also capable of two-way communication with ATC radar. In certain radar coverage areas — primarily near Class Bravo and Class Charlie airspaces — a Mode S transponder receives traffic information from ATC. This information can then be plotted on compatible GPS equipment to create a simple traffic information system (TIS).

There are some other things about transponders that are interesting, including the fact that there are special squawk codes a pilot can use in certain emergency situations. And although the transponders were turned off on the 9/11 airliners, that didn’t make them invisible; it just made it impossible for ATC to definitively identify what they were.

What the Stuff You Should Know Guys Said

There’s no transcript available for the podcast, so I had to create one for the part that irked me. It was related to when the transponder is turned on and what the transponder is/does.

At 22:55, Josh has just described how the tower controller hands off the airplane to a departure controller.

Chuck: All right, so now we’re in the air, we are enroute. And you have to, if you’re a pilot, activate your transponder, which will basically make you the little blip on the radar. Very important thing to do.

Josh: Yeah.

Chuck: That’s how they can follow you as you move across the country. Or around the world.

Josh: [laughter]

Chuck: Right?

Josh: You are covering all bases on this episode.

Chuck: Well, the little blip is going to obviously represent your plane and it’s going to have your flight number, your altitude, your airspeed, and your destination.

Josh: Uh-huh.

Chuck: And, uh, so where are we now?

Josh: It’s also how they find you if you go plummeting into the ocean or the earth.

Chuck: Sure. Is that the black box?

Josh: Uh, I think that’s probably a part of the transponder.

Chuck: Okay. Yeah.

Then they continue talking about what TRACON does.

What’s Wrong

There are a few things wrong with this.

First, a pilot usually turns on the aircraft’s transponder when he (or she, of course) powers up the rest of the avionics, including the radio. On my helicopter, in fact, the transponder turns itself on automatically when I turn on the “Master Battery” switch, which provides electrical power to the helicopter before I even start it.

Part 4-1-20 of the Aeronautical Information Manual (AIM), “Transponder Operation,” states:


(The FAA used those caps; I didn’t. I guess they wanted to shout about it.)

So the FAA says to turn on the transponder before you move the aircraft and keep it turned on during flight. The pilot does not wait until the flight is turned over to departure control to turn it on. It’s already on. In fact, it’s one of the ways ground control can track the airliner as it taxis between the runway and the gate.

Note: I was fortunate enough to be able to visit the Phoenix TRACON and tower back March 2012. I got to see the radar screens and their blips firsthand. It’s interesting to note that there are no windows in the TRACON facility. It’s a dark room filled with computer screens. If you’ve seen the movie Pushing Tin, which was mentioned in the podcast, you’ll get the idea.

So although the podcast guys made a big deal over the fact that ground controllers are only one of two kinds of controllers that can use binoculars, the reality is that only ground controllers and tower controllers have windows to look out of. They’re the only ones close enough to the airplanes they guide to actually see them.

To say that activating the transponder “makes you the little blip on the radar” is misleading. Radar does not need a transponder to see aircraft traffic. After all, do you think fighter planes use transponders when they’re out on patrol or attack? If a transponder was required to put an aircraft on radar, there would be no need for stealth technology. Instead, radar works by bouncing radio waves off objects. It doesn’t need a transponder signal. The transponder simply makes it easier for ATC radar equipment to find targets and provides additional information to ATC.

While it’s true that a radar blip might include an airliner’s flight number, this information is not sent by the transponder. The transponder sends the discrete squawk code assigned to the airplane from its flight plan. The ATC computer equipment looks up the code in the flight plan database and provides the information from the flight plan on the blip.

Josh is partially right when he says that the blip is how they find you if you crash. The transponder helps keep the aircraft on radar. Radar tracks where you are. But there comes a point — especially in remote or mountainous terrain — when radar coverage is limited. If you are flying too low, you can literally fly “below the radar” and not be tracked. Helicopter pilots commonly fly this low — that’s why its so difficult to get flight following in certain areas. An airliner should never be that low, but if it’s having trouble, it may disappear off radar before an actual crash. So although a transponder and the resulting radar blip can help locate a downed aircraft, it doesn’t guarantee that it’ll be found. Think about Steve Fossett. His plane likely had a transponder, yet he wasn’t found for well over a year after his crash.

Chuck and Josh are completely wrong when they suggest that the black box is part of the transponder. It’s not. They’re two completely separate devices. The transponder sends live information to ATC as an aircraft moves around on the ground and in the sky. Most aircraft have them. The black box is a virtually indestructible device that records data during an aircraft’s operation and stores it in the event of a mishap. Only aircraft providing certain air transportation services have them. For example, although I have a transponder on my helicopter, I don’t have a black box.

It’s interesting to me that the guys got this so wrong when the How Stuff Works website actually has an article called “How Black Boxes Work.” Maybe they should have read it?

Other Things

In listening again to parts of the podcast — mostly to find the passage quoted above — I heard other things that weren’t quite right. That bugs me. It calls into question the rest of the podcast — the stuff I don’t already know for sure. It also calls into question other podcasts that these guys do. How factual are they?

When I’m listening to a podcast titled “Stuff You Should Know,” I expect it to be factual, not conjectural. If these guys are guessing about something, they should make it clearer that it’s a guess. To state that a pilot activates a transponder after the aircraft is enroute and handed off to departure control is an incorrect statement of fact. To say “I think” a transponder is part of the black box helps identify it as conjecture or a guess, but is there really any place for guesses in a podcast like this?

Or am I expecting too much?

The Real Cost of Helicopter Ownership

Don’t believe what they tell you.

My first helicopter, a Robinson R22.

N630MLMy R44, parked out in the desert at a rides event.

Twenty years ago, if someone told me I’d own a helicopter before my 40th birthday, I would have told them they were nuts. Yet on October 3, 2000, I took delivery of my first helicopter, a 1999 Robinson R22 Beta II. Four years later, on January 8, 2005, I’d traded it in for a brand-spanking-new, designed to my specifications, 2005 Robinson R44 Raven II.

I was making a lot of money as a writer back then. A handful of bestselling computer how-to books — yes, they do exist — and a few good real estate investments left me with an excess of cash. I live rather modestly in a home I can afford and although I own more than my fair share of motor vehicles, none of them are new, flashy, or expensive. In other words, I don’t live beyond my means. Although my income fluctuates wildly — especially these days — I could foresee the ability to own and operate an R44 into the future, especially with added income from a small Part 135 on-demand charter operation.

Fueling my opinion on this matter was a document published by Robinson Helicopter Company on its Web site. Titled “R44 Raven II Estimated Operating Costs,” it painted a rosy picture of an “affordable” helicopter (if there is such a thing). The conclusion at the end of the “Operating Cost-Per-Road Mile” section stated that the calculated 98¢ per road mile “…compares favorably with some expensive automobiles, and will usually be lower when the value of time saved is considered.”

The Underestimated Costs

I knew from the start that the document was overly optimistic for my situation. Some of the numbers just didn’t seem right.

Arguing with a True Believer

It’s a waste of time.

I’m a skeptic. I’ve been a skeptic for at least the past 10 years, although I didn’t have a label for it way back when. After realizing that there was no proof in a lot of things I’d been told to simply believe, I started looking at things with a more skeptic eye. Although you can’t prove a negative — for example, something doesn’t exist — you can withhold believe until proof of the positive. That’s where I sit now.

Mary’s Mother

It’s also where I sat a few days ago when a house guest brought up the topic of a person’s spirit continuing to exist after death. When she — we’ll call her Mary (not her real name) — asked me whether I believed a person’s spirit existed after death, I said, without hesitation, no. She then launched into a long story about why she believed that spirits do go on after death.

It was kind of pitiful. Mary’s mother had died about two years before after about a year of declining health. Mary lived in California. Her mother lived in New York. Her mother was financially stable and had hired in-home nurses to care for her as she began the dying process. She’d been an alcoholic for most of her life and although she was always upbeat and fun, her last months were painful. Mary believed that the Hispanic nurses had held back on pain medication until her mother “accepted Jesus” — not very likely, as she was Jewish — and, as a result, her mother’s eventual death was more painful than it should have been.

Mary and her brother visited during the months their mother’s health was declining. In the end, they stayed until it was over.

Mary claims that a few days after her mother died, she had a dream that convinced her that her mother had died “a horrible death.” (I have trouble believing that, as she was fortunate enough to die at home with family nearby.) Mary claimed that her mother’s spirit was trapped in her house, unable to escape to whatever other place spirits are supposed to go.

Desperate to resolve the situation and save her mother’s tortured spirit, she sent a family member to the now unoccupied house to tell her mom to leave. (Mary was back in California by this time.) I don’t know if this family member actually did this.

Mary then contacted a psychic in California for assistance. I didn’t get all the details on the first contact. Apparently, Mary e-mailed the psychic a photo of her mother. I don’t know if she provided her mother’s name. In any case, they spoke by phone and the psychic managed to convince Mary that she could communicate with her dead mother. Tarot cards were involved; Mary didn’t understand why she needed them but was willing to put that aside. She told Mary that her mother was indeed trapped in her home and that the only way to free her spirit was for three people in three different places to light candles and play her mother’s favorite music and pray to her mother to “cross over.” I think they had to do this for three days in a row, but I may have that wrong.

So Mary asked her husband and cousin to do this. She did it, too. She says she’s not sure if her cousin did it.

Afterwards, she met with the physic in person. The psychic told her she did not remember their initial contact. She asked the psychic about her mother’s spirit. The psychic said that her mother’s spirit had been trapped but then something had “popped” (her word) and her mother had crossed over.

Mission accomplished.

I don’t know how much money exchanged hands, but I know Mary can afford whatever it was. And I do know that Mary is happy now, so I guess you can easily argue that no harm was done.

I’m not quite that generous, though.

Cold Reading

What followed was a discussion of cold reading, where a “psychic” makes a bunch of guesses and then reads his subject’s response to zero in on actual facts. It is documented that the human mind is more likely to remember correct guesses than incorrect ones. So if a “psychic” does a “psychic reading” and makes 5 correct yes/no guesses, 9 yes/no misses, and one direct hit, people come away thinking that the “psychic” has real psychic power.

Of course, John Edward came up in our conversation. Mary fully believed in his power. She had examples of “proof” of his power. She was not interested in the fact that every John Edward Crossing Over show is taped and then edited. They edit out the discussions he has that result in mostly misses and leave in the results that are mostly hits. The result might be something like this, which I don’t think is very convincing:

Did you watch this video? This is classic cold reading. Throwing out a common name, picking the person who responds, and asking questions to get information. Guessing all kinds of things that are relatively common — cancer, military service, etc. Pulling info out of people with questions. And they think he has real power. But listen carefully. How much is he actually getting right? How much is he telling them? Isn’t it more of a fishing expedition to suck information from people who already believe in his ability?

As Joe Nickell writes in his piece about John Edward:

The “psychic” can obtain clues by observing dress and body language (noting expressions that indicate when one is on or off track), asking questions (which if correct will appear as “hits” but otherwise will seem innocent queries), and inviting the subject to interpret the vague statements offered. For example, nearly anyone can respond to the mention of a common object (like a ring or watch) with a personal recollection that can seem to transform the mention into a hit.

I could not convince Mary. She was not willing to believe in my explanation of how he could have gotten a particular detail correct. The discussion got heated. She kept trying to convince me. I could not be convinced about a “trick” when I knew how it was done.

What I find particularly disturbing about all this is that Mary has a PhD in psychology and treats patients with particularly troubled backgrounds. She should be the voice of reason in these people’s lives. I hope that “woo” does not find its way into her diagnoses or treatments.

Another Friend

When I tried to relate this story to another friend of mine, he said two conflicting things in the same sentence: “You know I’m skeptical about all kinds of things, but I really believe the psychic I go to has real power.”

It was difficult for me not to explode with laughter.

He then went on to tell me about what was likely a personal, one-on-one cold reading. He’d make an easy subject. He’s a real talker and it wouldn’t take much to pull information out of him. He’s also willing to believe, which makes him more likely to remember hits more than misses or turn partial misses into hits by voluntarily providing information that makes a wrong guess right. This is why true believers will always continue to believe. They don’t understand that if a person had real psychic power, he/she should be able to make far more factual statements than errors. And the technique wouldn’t be a glorified guessing game, like the one John Edward plays on his television show.

My friend told me I should go see his psychic for proof. He’d set up an appointment. He’d tell her that I was a skeptical friend —

I stopped him right there. I told him I’d go, but only if he didn’t tell her a single thing about me — including my name. He didn’t seem to understand that she could simply Google me to learn all kinds of things about me that would be useful in her “reading.” It wouldn’t be a cold reading anymore; it would be a hot reading. She could simply recite things off my bio.

Will I go? Only if I’m sure she doesn’t know anything about me when I arrive. I may throw out my first name to see if she takes the hispanic bait (in Arizona, it’s far more likely for a woman named Maria to be Mexican than Italian). I’ll likely dress myself up a bit to alter my appearance and lead her to believe things about me that might not be true. I think these would be good tests of her ability to read minds rather than physical appearances. It would be an interesting experiment.

After all, I am a skeptic. Although I don’t believe that anyone has psychic power, I’m willing to let them try to prove that they do.

Vaccine Insanity

When doctors join in on the fear mongering.

FluViewI’ve been wanting to get an H1N1 Flu Vaccine for a while now. I believe that by getting the vaccine, I’ll not only protect myself from getting the Swine Flu, but I’ll prevent myself from becoming a carrier that can infect other people. In other words: I’ll do my part to help protect my fellow citizens and possibly prevent deaths.

When I heard the vaccine was available in town, I started making calls to see where I could get a shot. The Safeway Supermarket pharmacy ran out of doses yesterday. They suggested that I call my doctor. I did. And that’s when I got a shock.

A receptionist answered the phone. When I asked about the H1N1 Vaccine, she told me the doctor wasn’t giving shots. When I asked why, she replied:

The doctor heard that there were serious neurological side effects to the vaccine. She doesn’t think it’s safe.


I asked the girl for details and she had none. I asked her to have the doctor call me. I hung up and went to Twitter. My query there brought links to two reliable sources of information about the vaccine:

I read the information on both pages. Neither discussed any likely serious side effects. The CDC piece did mention the usual flu vaccine side effects but said the H1N1 vaccine was no more likely than any other flu vaccine to result in those side effects. It also mentioned Guillain-Barré syndrome (GBS), which was apparently an issue back in 1976. The article said that studies had been done and that the risk of GBS was 1 additional person out of 1 million.

Let me repeat that: 1 person in 1 million.

Is this the kind of risk that worried my doctor?

The phone rang. It was the receptionist at the doctor’s office. She told me that the doctor had read about the risks online, but she couldn’t remember where. (Fox News? I wondered.) She’d also heard about it from patients. (Now patients are advising doctors?) And she’d also heard it from a few doctors.

In other words, it was hearsay from vague, unidentified, and mostly unqualified sources.

Stay home if possible when you are sick. Visit for more information.

I told her what I’d learned from the CDC. She wasn’t interested. She wanted to argue with me. Evidently, the doctor’s sources were more valid than the Centers for Disease Control of one of the most advanced nations on the face of the earth. She wouldn’t listen to reason, she wouldn’t give me a chance to speak.

So I hung up on her. Why should I waste my time listening to a raving idiot?

I’ll be looking for a new doctor. Again.

And I’ll keep looking for my vaccination.

You want more information from the CDC? Start here.

You want some satire on the whole vaccine idiocy? Check out this on the Onion.

The Offending Pickup Truck

A photographer’s dilemma.

If you’ve been reading this blog for a while, you might be aware that I’ve been fooling around with panoramas. Last night, I created a panorama from 11 vertical images shot at Monument Valley:

Monument Valley Panorama

The ability of Panorama Maker 5 to stitch these together so perfectly sold me on the product. I bought it as soon as the stitched image appeared on my laptop screen so I could save my latest creation at full-size. The resulting image is a whopping 16,724 × 3,485 pixels in size and weighs in at 37MB — as a JPEG file.

Silver Pickup TruckOn close examination of the photo, however, I realized that there was one thing that marred it: a silver pickup truck dead center of the image (see red box above and blowup right). It wouldn’t be so bad, but the darn truck is shiny and really does stand out when you look at the image in full resolution.

So the question is: Do I Photoshop it out?

I experimented with this and did a reasonably good job with the cloning tool. But then I got to thinking about it. To me, a photograph represents reality. The reality of this image is that a silver pickup truck driven by what looks like a Navajo man was there when the image was shot. Removing the truck removes part of the reality of the image.

Or am I over analyzing this? Putting ethics where they don’t belong?

Are you a photographer? If so, how do you feel about modifying images to remove unsightly elements? If you’re not a photographer and just like to look at photos, how do you feel about a photographer’s honesty when creating and sharing photographic images?