Aeromedical Forum

As I sit in my office at Airlake, a King Air is revving up its engines. Good Lord it's loud and I have the benefit of 30 yards separation and a wall between me and it. Pity the lineman that's out there waving his batons. Ever since Wilbur and Orrville ran their Flyer down the sand at Kitty Hawk the business of powered flight has posed a threat to the hearing of pilots. So how to retain what hearing you have after an adolescence of rock concerts? First of all, let's talk about sound. You may remember from your fun physics class that sound is a form of mechanical radiant energy transmitted through the air by pressure waves. So sound waves are variations in air pressure above and below the ambient pressure. These sound waves have three characteristics: frequency, intensity and duration.

Frequency is what gives a sound its pitch. It is usually measured as wave cycles per second, called Hertz (Hz). Humans at best can hear sounds within a range of 20 to 20,000 Hz, with highest sensitivity between 500 and 4,000 Hz. Normal conversation takes place between 500 and 3,000 Hz.

Intensity is basically loudness, proportional to the sound pressure level. It is measured in decibels (dB). A perfectly normal ear can hear from -10 to +25 dB. If a pilot cannot hear a sound below 25 dB in intensity, he probably has had significant hearing loss.

Duration determines the potential risk of hearing damage when exposed to high-intensity sound. As you might expect, short-duration exposure to a high intensity sound can be as damaging as long-duration exposure to a less intense sound.

Many things in aviation can generate a lot of noise: power plants, jet efflux, propellers, rotors, hydraulic and electric actuators all add to the cacophony. Yet among all that unwanted clatter are critical sounds a pilot must hear-sounds of a normal-functioning aircraft or a not normal-functioning aircraft, those friendly reminders from ATC or other pilots on CTAF.

So what can a pilot do to preserve ear function: earplugs, earmuffs, communication headsets or active noise reduction (ANR) headsets. These protection devices reduce noise waves before they reach the eardrum. They are most effective at reducing high frequency noise above 1,000 Hz. Headsets have the added advantage of reducing background noise, making speech signals clearer and more comprehensible.

• Earplugs provide an inexpensive means of providing hearing protection. It is important that they make an air-tight seal in the ear canal. If you are working on the tarmac it's a really good idea to have a pair in your pocket.

• Earmuffs are another good idea if you are working around aviation operations. Commercial models are available online and are pretty effective.

• Communication headsets provide the pilot with the advantage of earmuffs with the ability to communicate with ATC and other pilots.

• Active Noise Reduction (ANR) sometimes called Active Noise Cancelling (ANC) headsets are an excellent investment for the active pilot. They provide superior noise reduction and improved signal-to-noise ratio compared to the older communication headsets. For a long cross country flight they really can reduce aural fatigue.

So if you haven't already, save your pennies and seriously consider upgrading to ANC. It will reduce your stress levels and enhance your performance in the cockpit on those long haul slogs!

Want more information? The FAA has a dandy link:

http://www.faa.gov/pilots/safety/pilotsafetybrochures/media/hearing.pdf

Fly wisely. See you next month.

As always, comments, questions and suggestions are welcome: jdlakinmd@gmail.com.

Also, we've moved our office to Airlake Airport's FBO (KLVN)! Call 952-469-4414 for a flight physical appointment.