Noise Fatigue

Fortunately, I've suffered little hearing loss in my flying career, partially because I've been religious about wearing the best active noise reduction headset I could find since ANR became available to the pilot public.

My first ANR headset was a David Clark with a separate battery box that required me to carry large quantities of AA batteries all over the world. A fresh set of AA batteries was good for about four hours, so a typical 10- to 12-hour leg across the Atlantic or Pacific demanded several cards of batteries.

As most pilots know, ANR isn't a terribly complex solution to noise pollution. A simple one-dimensional ANR system consists of a microphone and speaker that analyzes sound coming into a headset and transmits a waveform that's exactly counter to the noise source, effectively cancelling most of the offending sound.

ANR is most effective at nulling low-frequency sound, and the technology has been around since the 1950s. One of its most publicized practical applications was on the round-the-world, unrefueled trip by Dick Rutan and Jeana Yeager in Voyager in 1986. Bose provided experimental headsets for the two pilots on their unrefueled circumnavigation of earth.

Since then, ANR has been developed to lighter and more efficient designs that have progressively come to attenuate both aircraft noise and any other form of noise pollution. Today, you can buy receive-only ANR headsets for as little as $100 that will suppress sound levels in all manner of machines.

The technology has advanced significantly in the last 30 years, and today, there are several headset manufacturers that produce sets that offer as much as a 25 to 30 dB reduction for as long as half a day. A few manufacturers even allow tying in to aircraft power for unlimited noise attenuation.

Aircraft manufacturers have generally given short shrift to noise attenuation and have consistently concentrated instead on the more glamorous aspects of flying, namely performance. That's not so surprising when you consider that performance sells, and turning down the noise level isn't of much interest to most buyers.

Part of the problem is that hearing loss is insidious. It manifests itself gradually over a period of years, and you probably won't notice that your aural acuity is diminishing. A certain amount of hearing loss is normal as we age, but some people who work or play in noisy environments exacerbate the problem.

Piston aircraft are among the worst offenders, partially because the general aviation fleet averages 35 years old. More than coincidentally, in 1979, the industry was enjoying one of the biggest sales years in modern history. Over 18,000 personal and business aircraft were sold that year, and the manufacturers were so busy trying to meet demand that there was little time or motivation to worry about improving noise suppression.

Most pilots don't always understand the temporary and permanent effects of noise fatigue, partially because headsets have become so effective at suppressing sound levels. In fact, Bose and several other companies produce commercial receive-only headsets for music, airline entertainment system use and other applications where noise levels are high.

My current Mooney is from the same era, and I wasn't aware that the gear warning on my airplane wasn't working until it was discovered on the last annual. Fortunately, that fact has been masked, because I haven't been dumb enough to need the gear warning!yet. I now use either a Bose A20 or Lightspeed Zulu.2, both of which offer such excellent noise suppression, I never would have heard the telephone bell warning even if it had been working.

There was an interesting clip circulating on YouTube a while back of an over-the-shoulder perspective, probably shot with a GoPro mounted to the ceiling of an Aerospatiale Trinidad, approaching a private strip in France. The pilot and copilot were wearing ANR headsets and concentrating on the approach to the airport, totally ignoring the bleating of the gear warning horn. The recording included sound, and the horn was blaring away on a two-mile final. The Trinidad flared to a near-perfect touchdown with the wheels still tucked firmly in the wells. Fortunately, the airplane skidded to a stop pretty much straight ahead, and the only damage was to the owner's ego and bank account. All of that could have been avoided if the gear warning had been channeled through the audio panel into the headset.

At least some people are beginning to pay a little attention to noise suppression. For several years now, Beech has offered a three-dimensional ANR cabin noise reduction system on the King Air line. Other manufacturers of upscale turbine aircraft are beginning to copy Beech's design or build their own systems that help turn the entire cabin into a quiet zone.

Power Flow Systems in Daytona Beach, Fla., pioneered tuned exhausts for a variety of general aviation aircraft starting in the early 2000 time frame. These systems delivered as much as a 10% recovery of lost horsepower simply by minimizing "out the pipe" loss. I installed one on my Mooney in 2005 and saw an immediate three- to five-knot speed improvement. Diamond Aircraft tested the system and was so impressed, they elected to install it on all their Diamond Star singles.

More recently, however, Power Flow also began offering a quiet exhaust system designed specifically to dampen noise level without constricting power. My airplane is probably one of the worst offenders, producing an interior cabin noise level that would certainly leave me deaf as a post without protection. I was eager to see if the new exhaust pipe made a difference. (In fact, the noise is so loud on takeoff, it overpowers even the Bose A20 ANR during the takeoff roll.)

I installed one of the Power Flow Quiet Pipes during my last annual, and the difference has been dramatic. Darren Tilman, general manager at Power Flow, brags of a 13 dB drop in noise level inside the cabin on takeoff, and considering that decibels are measured logarithmically, that's a huge reduction.

On my first flight with the new exhaust stack in place, I was surprised that engine noise no longer overpowers my Bose A20s or Lightspeed Zulus. There was nothing subtle about the difference in noise level.

Power Flow sells the Quiet Pipe for $790, but unfortunately, it's only applicable to the 200 hp Mooneys already fitted with the Power Flow tuned exhaust. It's most effective on the older M20E Chaparral and M20F Executive models.

These days, there are a wide variety of ANR headsets to fit practically any budget. I can almost guarantee you'll hear a dramatic reduction in noise level. Or more accurately, you won't hear it.