I flew to my favorite breakfast stop recently, had a great brunch and then headed back to my home airport.
The weather was great and the winds were light so I decided to take a little shortcut over a low ridge rather than follow the road winding through the valley as I often do.
As usual in cases like this, as soon as I got to the ridge and out of gliding distance to any reasonable landing spot the engine suddenly sounded like it was going to come apart. It sounded like it was missing terribly and backfiring almost constantly. I had been in a nice, relaxed after-a-meal state and immediately sat bolt upright and grabbed the stick and throttle. My heart was pounding and my brain was churning faster than the latest i7 processor trying to calculate the Ultimate Question of Life, the Universe and Everything.
What’s the first thing you are supposed to do? I think I mentioned this before – wind the clock. The intent is to slow down and take stock of what you have to work with and how long you have to do the work. Here’s where this got interesting.
The first thing I noticed is that there was no vibration in the stick or throttle to go with the sound. Hmmm. All the engine instruments looked normal. Hmmm. Epiphany. I took off my headset to get a better read on what was going on. There was the normal wind noise and the nice smooth engine noise that you always want to hear. I put the headset back on and the awful sound returned. Hmmm.
I was wearing a David Clark active nose-cancelling headset. I turned off the noise-cancelling feature and the noise stopped. Cancel the emergency! It had been a while since I last flew and apparently the batteries in the headset unit were strong enough to get me to breakfast but only half way back. They had chosen that time to drop down below the threshold that the headset needed to function properly. The noise-cancelling function was cutting off and on in a rapid uneven sequence as the batteries dropped below the required level and then recovered.
I left the noise-cancelling function turned off for the remainder of the flight and changed the batteries when I got back on the ground. I carry an extra set of batteries and they can easily be changed in flight but I was flying solo I didn’t want to divide my attention while I flew.
Besides, I had to let my heart rate slow down to normal before I entered the traffic pattern.