Transponders – How My Plane Became a Stealth Aircraft

Think about your training and experience as a pilot — you covered stalls, turns, takeoffs, and of course, the always exciting landing, but there was probably something missing. Most pilots worked on their skills at minimum controllable airspeed, and depending on when you certified, you may even have had to do a few spins to get your ticket. When you consider the training that a person has to go through to become a licensed pilot, you would think that most everything that could happen would be covered … or would you?

I had rented a well-maintained Cessna 172 from the local FBO, and had set my course for a local airport. The airport was located at the center of a TRSA, or Terminal Radar Service Area, which — at the time — was a Junior ARSA. This meant that you were not required to report while in the airspace, but you should … just to be safe.

Since I was inbound for landing, I picked up the ATIS, then contacted Approach on the correct frequency and reported my intentions. Approach gave me a transponder code, which I dialed into the Cessna-provided unit, and plunged on towards the airport. Then things got a little weird

The first indication that something was wrong when ATC didn’t respond with their usual “Radar Contact, 15 miles southeast of airport.” Instead, I got something that was far less committal — ATC asked me to ‘turn to a heading of 360 for ID.’ I repeated back the instruction and made the turn. As a relatively new pilot, I had never heard this type of request from ATC before, but didn’t ask why I was asked to turn for ID. This was Mistake #1.

As I flew on, I received a second request from ATC to “turn for ID.” Something clicked in my mind and I took a good look at the transponder in the plane, which was turned on and set to the assigned squawk code … as it should have been. The interrogate light didn’t seem to be flashing, but pushing the test button made it brighter.

They say that when you fly, you should always ‘think ahead of the aircraft.’ Well, I’d been so distracted this odd new procedure and figuring out what was going on that — the next thing I knew — I’d been guided to within one mile of the airport. I remember the runways were clearly visible in the twilight. ATC was fairly busy with landing and departing jet traffic, and their lack of attention really wasn’t bothering me — the last time I had flown in, they had waited until I was only a mile or two out before handing me over to the tower.

Then came the radio call that cleared up all the confusion.

Cessna 97E, have neither primary nor secondary radar contact at this time,” the controller said. “Do Not Enter Airport Traffic Area. Repeat. Do Not Enter Airport Traffic Area.” Of course, I was already within the traffic area, and immediately turned on my landing light to lower the chances of being involved in a mid-air. Then it got worse: “Uh, 97E, what is your position?” the controller asked. I confessed that I was over the southeast end of the airport, at which point the controller said, “Oh, is that you?” and then cleared me to land and had me contact the tower.


  1. PILOTS: When things go wrong or not quite the way you expected, listen to the cues. I should have picked up on not hearing the expected “Radar Contact” reply from ATC, and questioned ATC on the absence of the transmission. Had I done so, I might have been able to figure out what the controller was doing earlier, and avoided the whole problem by returning to the airport for repairs.
  2. CONTROLLERS: Confess early. Just as pilots are encouraged to explain when things get out of whack, if you have a problem finding an aircraft, don’t just assume the pilot will be able to divine your intentions … tell them E A R L Y.
  3. TRANSPONDERS (Part I): If it dies, you are flying a stealth airplane. Unless ATC has a good idea of where you are — without the “Primary” signal from your transponder — they must rely on the weak “secondary” pulse they get from active radar. Again, unless they know where you are, spotting that pulse in a busy tower can be darn difficult.
  4. TRANSPONDERS (Part II): The transponder interrogate light was dimmed down due to the lighting systems on the Skyhawk — at the time, I didn’t know that. Suffice to say, pilots should be familiar with how fast the interrogate light flashes on their plane on a typical day in different airspace and take actions to investigate problems when the equipment doesn’t act as it usually does. Had I noticed the interrogate light’s performance in my look over the panel, I might have had an opportunity to figure this out before it became an unintentional airspace violation.

BOTTOM LINE: Learning about your aircraft and the airspace we fly in is part of what makes flying fun … and part of what makes you a better pilot. Even the most mundane flights have something to offer and — take it from me — the best time to learn about your airplane is when you don’t have to. In the case above, the transponder was just one little thing that I needed to learn a little bit more about. It would have been a bit better if I’d learned about it before being directed over an active runway.