University of California
Type of paper: Thesis/Dissertation Chapter
One philosophy that some persons question, including a few of our own aviation medical examiners, relates to our greater flexibility in granting special issuances to private pilots as opposed to air carrier and other commercial pilots. The arguments against such flexibility rotate around the thought that, in the event of a medical incapacitation, an air carrier or commercial pilot usually has another pilot on board who can take control of the aircraft and safely land. In contrast, the private pilot often has no such “safety net” and, therefore, a medical incapacitation is likely to have severe safety consequences. In the case of the private pilot, I think we can be more flexible and allow that pilot to assume some risks for him or herself that we would not permit in air carrier or other commercial operations.
This philosophy is frequently challenged regarding the safety of persons who fly as invitees of the private pilot. The risk derives not only from the medical status of the pilot, but the pilot’s proficiency and experience as well as the airworthiness of the aircraft. One might suggest that our approach, allowing greater flexibility in the medical certification of private pilots, constitutes experimentation with safety in private operations. This suggestion might have some validity if private pilots who are granted special issuances experience a significant number of medically related accidents. Humans regard vision as their most valuable sense, yet they fail to appreciate what a remarkable and complicated organ the human eye is. The rods are concentrated in a ring around the cones. Both the cones and the rods are used for vision during daylight and bright moonlight.
The pilot should consciously practice this scanning procedure to improve night vision. It is important for the pilot to maintain good physical condition. While dim red lighting has the least adverse effect on night vision, it severely distorts colors. Older pilots may experience extreme difficulty in focusing the eyes on objects inside the cockpit. In addition to night vision, the pilot should also be aware of how to cope with illusions encountered during night flight. Refer to Advisory Circulars 61-23B, “Pilot’s Handbook of Aeronautical Knowledge,” and 61 21A, “Flight Training Handbook,” and the Aeronautical Information Manual for further information on the above subjects. The term hearing describes the process, function, or power of perceiving sound.
The sense of hearing makes it possible to perceive, process, and identify among the myriad of sounds from the surrounding environment. Anatomy and Physiology of the Auditory System The auditory system consists of the external ear, ear canal, eardrum, auditory ossicles, cochlea (which resembles a snail shell and is filled with fluid), and the auditory nerve. Ambient sound waves are collected by the external ear, conducted through the ear canal, and cause the eardrum to vibrate. Sound waves are variations in air pressures above and below the ambient pressure. All sounds have three distinctive variables: frequency, intensity, and duration. Frequency is the physical property of sound that gives it a pitch. Since sound energy propagates in a wave-form, it can be measured in terms of wave oscillations or wave cycles per second, known as hertz (Hz).
Sounds that are audible to the human ear fall in the frequency range of about 20-20,000 Hz, and the highest sensitivity is between 500 and 4,000 Hz. Sounds below 20 Hz and above 20,000 Hz cannot be perceived by the human ear. The decibel (dB) is the unit used to measure sound intensity. The range of normal hearing sensitivity of the human ear is between -10 to +25 dB. Sounds below -10dB are generally imperceptible. A pilot who cannot hear a sound unless its intensity is higher than 25 dB (at any frequency) is already experiencing hearing loss.
Duration determines the quality of the perception and discrimination of a sound, as well as the potential risk of hearing impairment when exposed to high intensity sounds. The adverse consequences of a short-duration exposure to a loud sound can be as bad as a long-duration exposure to a less intense sound. Noise The term noise refers to a sound, especially one which lacks agreeable musical quality, is noticeably unpleasant, or is too loud. In other words, noise is any unwanted or annoying sound.
Categorizing a sound as noise can be very subjective. The aviation environment is characterized by multiple sources of noise, both on the ground and in the air. Noise is produced by aircraft equipment-powerplants, transmission systems, jet efflux, propellers, rotors, hydraulic and electrical actuators, cabin conditioning and pressurization systems, cockpit advisory and alert systems, communications equipment, etc. All pilots know the sounds of a normal- functioning aircraft. The effects of pre-flight exposure to noise can adversely affect pilot in-flight performance.
Types of Noise
Examples: aircraft powerplant noise, propeller noise, and pressurization system noise. According to the Occupational Safety and Health Administration (OSHA), the maximum permissible continuous exposure level to steady noise in a working environment is 90 dB for eight hours. The eardrum may be ruptured by intense levels (140 dB) of impulse/blast noise. Effects of Noise Exposure
Ear discomfort may occur during exposure to a 120 dB noise.
Ear pain may occur during exposure to a 130 dB noise.
Eardrum rupture may occur during exposure to a 140 dB noise. Temporary hearing impairment. Unprotected exposure to loud, steady noise over 90 dB for a short time, even several hours, may cause hearing impairment. This effect is usually temporary and hearing returns to normal within several hours following cessation of the noise exposure. Permanent hearing impairment. Unprotected exposure to loud noise (higher than 90 dB) for eight or more hours per day for several years, may cause a permanent hearing loss. Subjective Effects: Annoying high-intensity noise can cause distraction, fatigue, irritability, startle responses, sudden awakening and poor sleep quality, loss of appetite, headache, vertigo, nausea, and impair concentration and memory. Speech Interference: Loud noise can interfere with or mask normal speech, making it difficult to understand. Tasks that require vigilance, concentration, calculations, and making judgments about time can be adversely affected by exposure to loud noise higher than 100 dB.
How to Protect Your Hearing
Limiting Duration of Exposure to Noise: OSHA-established permissible noise exposure limits for the workplace(Fiugure 2) (including the cockpit of an aircraft). Use Hearing Protection Equipment. If the ambient noise level exceeds OSHA’s permissible noise exposure limits, you should use hearing protection devices-earplugs, earmuffs, communication headsets, or active noise reduction headsets. Even if an individual already has some level of permanent hearing loss, using hearing protection equipment should prevent further hearing damage.
These protection devices attenuate noise waves before they reach the eardrum, and most of them are effective at reducing high-frequency noise levels above 1,000 Hz and/or for reducing noise levels to, or below, 50 dB. Earplugs. Insertable-type earplugs offer a very popular, inexpensive, effective, and comfortable approach to provide hearing protection. Communication Headsets. Active Noise Reduction Headsets. This type of headset uses active noise reduction technology that allows the manipulation of sound and signal waves to reduce noise, improve signal-to-noise ratios, and enhance sound quality. Active noise reduction provides effective protection against low-frequency noise.
The electronic coupling of a low-frequency noise wave with its exact mirror image cancels this noise. * Combinations of Protection Devices. The combination of earplugs with earmuffs or communication headsets is recommended when ambient noise levels are above 115 dB. Earplugs, combined with active noise reduction headsets, provide the maximum level of individual hearing protection that can be achieved with current technology. [Editor’s Note: Be careful you don’t muffle too much engine noise when you combine ear protection devices.
Aeromedical factors. (n.d.). Retrieved from http://www.free-online-private-pilot-ground-school.com/aeromedical.html Aeromedical factors. (n.d.). Retrieved from https://ntc.cap.af.mil/ops/dot/school/CAPF5_Course/aeromedical.htm Aeromedical factors: cfi lesson plan. (n.d.). Retrieved from http://cfi-lesson-plans.com/aeromedical-factors/ Aerospace medicine & human factors. (n.d.). Retrieved from http://aeromedical.org/avmed_home.php Office of aerospace medicine. (n.d.). Retrieved from http://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/cami/