I took off VFR and called Columbus, Georgia, Approach Control, which handles IFR operations at Auburn, to pick up my clearance to Page Field in Fort Myers, Florida. The controller was ready: "Five-Four-Yankee is cleared to Page as filed, climb to five-thousand, squawk three-five-four-five."
He acknowledged my readback of the clearance, and I reached over to set the transponder to the assigned four-digit discrete beacon code that would identify me on the controller's radar scope.
Hmmm...no bright amber glow on the face of the transponder to indicate that it is transmitting the beacon code in response to an interrogation from the approach control facility's ground-based surveillance radar. Maybe I'm still below radar coverage. Sometimes, an airplane in climb attitude shields the belly-mounted transponder antenna from the ground-based radar transmitter. Shallowing the climb attitude, or climbing to a higher altitude, fixes that problem.
The few minutes I gave it didn't fix things. I recycled the transponder - switched to Standby and then back to the altitude-reporting (ALT) switch position. I tried turning it off, waiting, then back on again. I tried a little boot maintenance - a few persuasive taps on the face of the unit. I tried pushing it in to ensure it was fully mated to the connecting pins in back, but all to no avail. No reply light, no identifying blip from Five-Four-Yankee on the controller's scope.
I asked the controller if I could "squawk ident" - push the Ident button on the transponder, which sends a transmission resulting in a strong blip on the controller's scope for quick, positive identification. Nothing showed up on the controller's display. Apparently, the transponder was completely inoperative.
Now what? I'd just taken off with my wife and son on a 450-nm trip home. Would I have to return to Auburn and try to get the transponder fixed on a Saturday? Would I be allowed to continue on my IFR flight? Or, would the controller offer me the alternative of canceling IFR and proceeding VFR without the benefit of receiving traffic advisories, even though my route would take me very close to Tampa and Orlando Class B airspace?
A transponder is a prerequisite for operating in controlled airspace. Federal Aviation Regulation 91.215 specifies where Mode A transponders with Mode C altitude-reporting capability are required (in general, in Class A, B, and C airspace, within the 30-mile "ring" around Class B airspace, above Class B and C airspace, and anywhere when above 10,000 feet mean sea level [msl] except for any airspace closer than 2,500 feet to ground level. Some exceptions apply, most notably to aircraft certified without electrical systems). The regulation also says that if the airplane has a working transponder with Mode C altitude-reporting capability, it must be on whenever the aircraft is operating in any controlled airspace.
Fortunately, the regulation also allows for some wiggle room in the event the transponder acts up. Specifically, it says that you may ask air traffic control for a "deviation" from the regulation so that you can fly to your ultimate destination, including any intermediate stops, or to a place where suitable repairs can be made. In other words, if you discover after taking off that the transponder isn't working, you don't necessarily have to return to the airport unless it makes sense to do so. The air traffic control facility responsible for the airspace you are in can waive the FAR 91.215 transponder requirement on the spot.
In my case, I didn't even have to make the request to the Columbus controller. When it became obvious my transponder wasn't functioning, he gave me a 90-degree turn to the left. The purpose of the vector was to identify me on his radar scope, to confirm that the primary target he was looking at as indeed my airplane. A primary target is the basic radar reflection of the aircraft skin, minus any transponder-supplied data - four-digit squawk code and altitude. When the controller saw that the primary target also made a 90-degree turn to the left, he knew for certain it was me.
Now that the controller had positively identified me on his screen and, with confirmation of my altitude, could track my progress and provide standard IFR separation services, he turned me back toward the southeast and my destination. Because of the inoperative transponder, the Columbus controller recleared me on a new course direct to a nearby VOR, and then on published airways all the way home. Radar coverage is good along airways, especially above 3,000 feet. Flying GPS direct off airways could have taken me over areas of sparse radar coverage.
The only unusual feature of the flight was that I was required to make several position reports. The Columbus controller instructed me to report crossing the first VOR. The next controller I talked to asked for my distance to the next VOR and the radial I was flying, to confirm the position of the primary target.
The fact that the Columbus controller quickly had me on my way despite the transponder problem didn't necessarily mean that every one of 10 controllers I was handed off to in six different ATC facilities on the flight home would be so accommodating. Radar coverage, traffic volume, weather - any or all of these factors can affect a controller's ability to handle a non-transponder primary target.
A transponder is virtually a required fixture in most general aviation aircraft. Fortunately, the FARs provide us with some options for asking for, and receiving, air traffic control services even if the transponder and/or its Mode C altitude-reporting capability is inoperative. When that occurs, our job is to fly well - to maintain an assigned altitude, to follow an assigned route, and to always know where we are and be able to report our position when requested.
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