Just when you thought knowing light gun signals would be useless, you find yourself flying with failed radios, a non-transmitting transponder, and a dying electrical system into a tower controlled airport. Oh yeah, and it's night. Sounds like fun, right?

How can something as simple as a radio failure be a sign of much more serious electrical problems in your airplane? That's what I found out a few weeks ago, while returning to Grand Forks International Airport after a local sunset flight with friends. So what happened to the electrical system in the 1968 Cessna 172I Skyhawk that I flew? And what caused my radio/transponder to fail before any other electrical components?

The First Warning Signs

It was a normal sunset flight with three friends, all commercial aviation students and pilots from the University of North Dakota. Flying at 2,000 feet and 5 miles away from the Class D airspace, problems started with the simple fading in and out of radio reception while approaching Grand Forks (KGFK). Imagine listening on the phone to someone with a bad connection; that's what approach control began to sound like. For about 5 minutes, we circled outside of the Class D airspace, calling approach, tower, and even ground control on every frequency possible. No response.

After turning both radios off and back on, nothing changed. Neither radio was working, and receiving any kind of transmission was becoming impossible due to a high pitched squealing noise through the headsets that sounded similar to a police siren.

Declaring An Emergency

"Ok," I thought, "now what?" When I realized the problem was getting worse, not better, I knew that I was being confronted with my first legitimate in-flight emergency. Flying circles outside of the Class D airspace, it was now well past sunset and light was fading fast. In reality, I had two options:

1) Divert to the nearest pilot-controlled airport with lighting to avoid towered airspace (Grafton KGAF was roughly 20 miles away). In this case, Grafton's lighting would've been on from sunset to sunrise, so we weren't worried about not being able to turn on lighting with the failed radio.

2) Find a way to contact Grand Forks tower to enter their airspace and land.

The four of us onboard decided to try the Grand Forks option first, since it was the closest airport with the most services available on-field. Remaining outside of the Class D airspace, I tuned "7600" into the transponder, a code used to tell ATC that we'd lost communications. For a few minutes, we continued circling, hoping that we would see light gun signals from the tower once they picked up our beacon.

But after a few minutes with no light gun signals visible, we moved onto the next option. That's where teamwork and CRM really came into play with my friends onboard...

The Problem We Couldn't See

Until we landed at the airport, all of us thought we were dealing with a simple radio failure. Keep in mind, the old 1968 C172I only has an ammeter installed. And with the ammeter reading a positive charge, occasionally bouncing to zero with the flashing of our old beacon light, we had no way of seeing exactly what was happening to the electrical system of the airplane.

There unfortunately aren't low voltage or alternator failure lights installed in the aircraft due to its age. And on top of that, the transponder's "on" light was blinking for the entire flight, regardless of whether it was transmitting or not. We had no way of knowing that ATC could not see our 7600 code. So until other aircraft components began to fail, it was an easy assumption to think we only were dealing with a radio failure. Only toward the end of our flight, once we were cleared for landing, did the ammeter begin reading a varying charge ranging from zero into the negatives.

Managing The Emergency

Jon Jensen, a student pilot sitting in the back seat connected his cell phone to a bluetooth Bose A20 headset and called the control tower's phone number (which he had coincidentally put into his phone the day before). Once the tower picked up, the phone and headset was given to Corey Komarec, a more experienced commercial student pilot.

And since our 1968 C172I only had an intercom installed in the two front seats, Corey (who was sitting in the back) relayed instructions to Timo Soroush (who sat adjacent to me in the right seat). Timo then relayed the instructions to me through the intercom, all while I was focused on flying. It was one big game of telephone, but with each person having a defined role in the emergency, managing the situation was easy. Jon provided a headset and phone number, Corey talked to the control tower, Timo relayed information to me, and I flew the airplane.

The Failure Point: The Voltage Regulator

An alternator only puts out power equivalent to that being drawn by the devices on the aircraft. For example, the avionics might only draw 12 amps and the voltage regulator adjusts accordingly so that the alternator only puts out 12 amps. If you then turn on a 6 amp landing light, the voltage regulator adjusts and enables the alternator to put out 18 amps. So if your voltage regulator fails, it's almost the same as having an alternator failure, something that most pilots are more familiar with.

In our case, the radio and transponder failed first, because those components draw more amps than most other systems do to operate.

If you experience a voltage regulator failure, you should follow steps similar to those found during an alternator failure.

In our case, with teamwork, light gun signals, and a phone call to the control tower, we were able to get on the ground quickly and safely. So if you're ever flying and begin to notice a piece of electrical equipment malfunctioning, especially one that takes a lot of amps to operate, start thinking about what could be wrong with your electrical system.