You may not realize it, but the commercial airliners we fly on have redundancy for virtually every onboard system. This, of course, is no accident—it’s a popular saying that the history of aviation improvements is written in blood, so the reason why we have redundant electrical systems, pressurization, and so on is because in the past, single points of failure have caused catastrophic accidents.
Even light airplanes often have more redundancy than the casual observer might suspect. For example, the engine ignition system in piston airplanes has two redundant magnetos, wired so that each magneto is independently providing spark to both cylinders. If one mag fails, no worries; you’ve got another one.
Luckily, the same is true with radios, as I found out on a recent night flight. My mission: leave Palo Alto, fly up to Napa to pick up my cousin, and continue on to Willows for dinner. I was in a fairly new G1000-equipped 172, one that I hadn’t flown before. When I listened to the ATIS broadcast on COM1 during my preflight, I noticed quite a bit of audio clipping, but I wrote it off as due to my position on the airfield– behind a large metal hanger with an electrical box that causes an audible squeal in the audio system as you taxi past it. I preflighted, started, and called ground; I could hear them OK, so I taxied to the runup area. Runup was normal, and then I switched to the tower frequency and called them for a takeoff clearance.
I called them again.
That’s odd, I thought. Even a busy controller will usually respond after a second call, and I’m the only guy out here anyway. A few seconds later the controller answered but his audio was unintelligible. I tried a couple more times, then switched back to ground and told them I was taxiing back to parking. When I got there, I started playing with the squelch controls on the audio panel while listening to the ATIS frequency and eventually got a squelch level that gave me clean audio… or so I thought.
Taxi back, runup, and takeoff were uneventful. I was talking to Norcal Approach the entire time; they vectored me over the San Mateo bridge, then over the runway 29 numbers at KOAK, then past the Nimitz Freeway, then VFR direct to the Napa airport. The trip was gorgeous, and I made a good landing at KAPC. Sadly I had forgotten my spare headset, and the local FBO didn’t have one, so Chris and I decided to have dinner in Napa instead of flying to Willows. We had a great visit while devouring burgers at Gott’s (where I had the best milkshake ever), then I dropped him back at the airport and got ready to fly back.
In the meantime, the Napa control tower had closed. This isn’t uncommon; many airports are towered only during part of the day. The normal procedure is to use the tower frequency (or another freq, if designated) to announce your position and intentions to any other aircraft in the area. I did so and had an uneventful takeoff. As I turned back towards the Bay Area, I tuned in the Norcal Approach frequency and called them.
Uh oh, that’s not good, I thought. I knew I hadn’t gotten the frequency wrong because I used the G1000 to enter it directly from the airport diagram, but I looked it up anyway and tried again.
By this time I was getting uncomfortably close to controlled airspace, and I didn’t want to enter it without being in radio communication with ATC, so I started a nice, gentle standard-rate turn to keep me out of trouble while I troubleshot.
First I tried calling Flight Watch, the nationwide FAA enroute advisory service that uses the same frequency, 122.0 MHz, everywhere. No joy.
Next I switched over to COM2 and called Flight Watch again. “Four Lima Bravo, we could hear you a minute ago but you couldn’t hear us. How copy?”
Bingo! My primary radio had gone dead.
While this was a little disconcerting, it wasn’t a problem; I had another completely functional radio, so I switched back to Norcal’s frequency, called them, got cleared along my route, and went about my business. If my secondary radio had failed too, I wasn’t without options; I could have changed my transponder code to 7600 to indicate that I was NORDO, then I would have flown a route and altitude to keep me away from Oakland and SFO. In this case, that basically means about 1500′ straight down the middle of the Bay. The Palo Alto tower was closed by the time of my arrival, so I would have had to be very careful about entering the traffic pattern (and as it turned out there were a couple of other planes working the pattern there).
Although this wasn’t an emergency by any stretch, I was glad to have that second radio. Operating in busy controlled airspace at night is not a good time to be muzzled. It might be time for me to pick up a handheld nav/comm radio to keep in my flight bag as a backup. (Of course, then I’d need a bigger flight bag…)