Original Research
Occupational Health & Audiology

Noise Exposure Among Maintenance Crews of C130H Aircraft Lead to the Hearing Impairment

Summary

Military aviation maintenance represents one of the most noise-intensive occupational environments. Aircraft maintenance crews working on the C-130H Hercules—a four-engine turboprop military transport aircraft widely used by air forces worldwide, including the Royal Malaysian Air Force (RMAF)—are routinely exposed to intense noise levels during engine run-ups, ground idle operations, and maintenance procedures. This sustained and repeated exposure poses significant risks to auditory health.

This study, published in the Malaysian Journal of Public Health Medicine, investigated the prevalence of hearing impairment among C130H aircraft maintenance crews in the RMAF. The research combined noise level measurements with audiometric testing to characterise the occupational hearing risk faced by this specialised workforce.

Study Population and Methods

The study was conducted at the Institute of Aviation Medicine, RMAF, and involved 63 maintenance crew members who worked on C130H aircraft. These personnel were exposed to aircraft noise during their 24-hour shift rotations, which significantly increased their noise exposure duration compared to standard 8-hour shifts. Hearing assessments were conducted using standard audiometric testing protocols, with hearing impairment defined according to established audiological criteria at frequencies of 4000 Hz, 6000 Hz, 7000 Hz, and 8000 Hz.

Noise level measurements were taken at various distances and positions around the C130H aircraft during different operational states, including ground idle. The measurements were compared against established Permissible Exposure Limits (PEL) to determine whether maintenance crew members were operating in hazardous noise zones.

Prevalence of Hearing Impairment

The audiometric results revealed that 41.2% of the sampled maintenance crew members demonstrated hearing impairment, failing audiometric testing at one or more of the assessed high frequencies. This prevalence rate is notably high and significantly exceeds that reported in many civilian occupational noise studies. For comparison, studies of aircraft maintenance workers in other countries have reported noise-induced hearing loss prevalence rates ranging from 22.9% in the Indian Air Forces to 33.5% in Saudi Arabian civilian aviation settings.

The elevated prevalence in this study may be attributable to several factors specific to the military aviation maintenance context. The 24-hour shift pattern means that maintenance crews accumulate noise exposure over longer periods than standard 8-hour shifts. Additionally, the C130H’s four Allison T56 turboprop engines generate substantial noise during ground operations, and maintenance tasks often require close proximity to running engines.

Noise Exposure Assessment

Noise measurements confirmed that areas around the C130H aircraft during ground idle and maintenance operations exceeded the PEL. The noise levels were particularly hazardous in zones immediately adjacent to the engines and in maintenance hangars where sound reverberates off hard surfaces. The study documented that maintenance crews working on shift for extended periods were highly exposed to cumulative noise doses exceeding recommended safe limits.

Control Measures and Recommendations

A critical finding of this study was that reliance on personal protective equipment (PPE) such as earplugs and earmuffs, while necessary, is insufficient as a standalone solution. PPE compliance may be inconsistent, particularly during prolonged shifts, and hearing protectors may not provide adequate attenuation at all hazardous frequencies. The study recommended that engineering controls—such as acoustic barriers, engine run-up enclosures, noise-dampening materials in maintenance hangars, and modifications to work scheduling to limit cumulative exposure—should be identified and implemented as the primary long-term approach to controlling noise hazards.

The hierarchy of controls in occupational health places engineering controls above administrative controls and PPE, as they address the hazard at its source rather than relying on individual worker behaviour. For military aviation maintenance, this may include investment in quieter maintenance equipment, improved hangar acoustics, and development of remote monitoring systems that reduce the need for close-proximity work during engine operations.

Implications for Military Occupational Health

The 41.2% prevalence of hearing impairment among C130H maintenance crews represents a significant occupational health burden for the RMAF. Hearing loss among military personnel has implications beyond individual health, potentially affecting operational communication, situational awareness, and career longevity. A comprehensive hearing conservation programme incorporating baseline and periodic audiometry, noise monitoring, engineering controls, and enhanced PPE training is essential.

Limitations

The study’s sample size of 63 maintenance crew members, while representing the available workforce, limits statistical power. The cross-sectional design prevents assessment of hearing loss progression over time. The study did not control for potential confounding factors such as recreational noise exposure, pre-existing hearing conditions, or years of service. Future research should incorporate longitudinal follow-up and detailed exposure histories to better characterise dose-response relationships in this population.

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