Say Again, Please
Preventing hearing loss in and around airplanes

Stanley R. Mohler, M.D.
Sport Aviation - November 2001

One of the highlights of EAA AirVenture Oshkosh is meeting old acquaintances and rekindling friendships. However, with each passing year I’ve become aware of a disturbing trend: More of my friends are wearing hearing aids, the result of longtime, unprotected exposure to noise that exceeds the human ear’s injury threshold. In many cases, longtime pilots, especially old-time racers and military pilots, require hearing aids later in life. The same is often true of mechanics and longtime line personnel.

You can protect your hearing by taking some simple steps when flying or working in or around loud noises, such as an aircraft engine or rivet gun, that can injure unprotected ears. Figure 1 shows the National Institute for Occupational Safety and Health noise energy limits at various frequency levels and exposure times. These levels are "recommended permissible" limits and provide a good base line for safety.

If you’re exposed to noise intensities and durations that exceed these limits, they can damage the inner ear’s delicate hearing mechanism. Short duration exposure to high levels of noise can cause a transitory shift of hearing threshold, but recovery to prior levels of sensitivity is possible over time. However, continuous or multiple exposures to high levels of noise can cause permanent shifts toward hearing loss at various frequencies.

The human ear has the ability to hear very faint sounds, including the buzzing of tiny insect wings. But this sensitivity can present problems in a high-noise environment. Too much noise energy can fragment and damage the sensory "hairs" in the cochlea (the inner ear) that resonate with various frequencies.

If you’ve ever used an ammeter you’ll have an idea of how excessive noise affects hearing. When a multiple ampere current (think noise) is thrown into the delicate meter when it’s set at the milliamp range (think sensitivity), damage to the ammeter occurs. That’s what happens when the ear receives noise levels that exceed its sensitivity capabilities.

The Incredible Ear

The human ear has a beautifully designed built-in noise protection mechanism. Three tiny bones-the anvil, the hammer, and the stapes, the little bone that looks like a stirrup-connect the eardrum and the cochlea. Between these tiny bones are cartilage and joint fluid, just like other skeletal joints. These little bones transmit sound vibrations from the eardrum to the cochlea, which detects the frequencies and intensities of impending sound or noise (noise being defined by some as unwanted sound) and transmits them to the hearing centers of the brain.

The body’s tiniest skeletal muscle is the stapedius, and it runs from the wall of the middle ear to the stapes bone. If the brain detects noise of an intensity that could damage the cochlea, the stapedius muscle contracts and partially pulls the stapes away from its connection to the cochlea.

Just as raising the drawbridge slows the attack of castle invaders, pulling the stapes away from its contact point somewhat diminishes the sound energy transmitted to the cochlea. This mechanism is nature’s way of providing some protection against hearing damage caused by excessive noise.

The same nerve system that can stimulate facial muscle contractions and cause a facial grimace controls the stapedius muscle contraction. This is why, in the presence of a loud noise, the facial muscles are stimulated at the same time as the stapedius muscle. The result can be a marked simultaneous facial grimace. But nature can do just so much in protecting our delicate hearing.

A Few Ounces of Prevention

Wearing hearing protection is the number one safety habit you can practice when exposed to an injurious noise environment-maintenance hangar, engine-testing facility, or workshop. A quality noise-reducing headset (the one that looks like an aviation headset without the electronics and microphone) is the best safety solution.

Simple earplugs can do wonders to protect your hearing and are readily available at aviation retail outlets or in catalogs. They’re inexpensive and comfortable and will last for years. They often come in a small plastic box attached to a key chain, and they can easily be made a standard part of your flight kit so they’re always handy. Disposable, one-time-use earplugs are also a convenient option for the flight bag or workshop.

When flying, use a quality aviation headset. The passive protection will help preserve your hearing, and a set featuring active noise-reduction technology will further protect your ears.

My first flying lessons were in Aeronca Champs and Piper J-3 Cubs, and serious training for my private certificate was in a Piper Tri-Pacer. In the 1950s and 1960s these lessons were sans headsets because many airplanes didn’t have electrical systems or intercoms. Instructors and students simply became accustomed to the 95- to 100-decibel cockpit.

Some minutes into the flight, the hearing threshold would rise, and the noise wouldn’t seem to be so severe. But on cross-country flights the continuous high-level noise contributed to flight fatigue. After the flight, it was common for the ears to "ring," and the return to normal hearing from transitory partial deafness took several hours.

Thankfully, protective headsets began seeing widespread usage in the late 1970s in general aviation as new materials and construction methods provided better seals around the ears along with added comfort.

Your goal should be to limit your exposure to excessive noise in all activities-not just during flying and building. Use hearing protection when engaging in target practice or hunting, when using chainsaws, lawnmowers, tractors, or other loud machinery, and during occupational activities involving excessive noise.

For more detailed information on noise and its effects on hearing, visit www.cdc.gov/niosh/noise/noisepg.html. or www.entnet.org/noise-hearing.html. 

Figure 1