HEARING LOST

The risk of hearing lost around aircraft

The risk of hearing lost around aircraft

Introduction

In recent years a number of surveys have been conducted in a variety of military aircraft. These have shown that even with the very best hearing protection some aircrew are still being exposed to a noise dose in excess of the current legislative criteria set out in the UK's Health & Safety Executive's (HSEs) Noise at Work regulations. This situation will be further exacerbated in February 2006 when new and more stringent noise legislation arising from the EU's Physical Agents Directive 2003/10/EC will become UK law.

The Ministry of Defence (MoD) considers personal protection (including hearing protection) a duty of care issue and aim to provide personal protective equipment (PPE) that is fit for purpose and that aligns with legislative criteria. The high noise levels that some aircrew are subjected to will, without adequate protection, cause permanent hearing damage which, in turn, will require aircrew to be downgraded from flying duties with the incumbent re-training costs for downgraded personnel and training costs for new/replacement aircrew.

Additionally, since 1987 when section 10 of the Crown Proceedings Act was repealed, military personnel have gained the right to sue the MoD for disabilities incurred during the course of duty. Hence, MoD will not only have to meet the costs of disability pensions but there is the added burden of compensation and litigation costs. A similar situation is found in the US, where the military pay out some $270m a year in service disability pensions related solely to hearing loss and it would not be unreasonable to assume that the UK figures will soon be proportionate.

Internal cockpit and cabin noise

The majority of the current problems associated with high levels of cockpit noise are generated, essentially, from the post 1960's need to fly operationally at high speed and low-level. These flight tactics were adopted in order to minimise detection by radar and exposure times to ground based weapon systems. Ingress to target is usually flown at speeds of around 420 to 480 knots at heights at, or below, 250 feet and egress is quite often lower and faster. At these speeds and heights noise levels in the fast jet aircraft cockpit have been increasing over the years, with one or two exceptions, and cockpit noise levels of 115dB to 120dB are now not unusual during high-speed, low-level flight.

Helicopter noise

Helicopters have a different mechanism of generating noise and the sources are both aerodynamic and mechanical. The cockpit or cabin noise is predominantly narrow band discrete tones with associated harmonics superimposed on a low-level, broadband background noise. Aerodynamically induced noise is generated from the main and tail rotors, including interactions between the rotors in a twin rotor design (e.g. Chinook) and interactions between the rotors and fuselage. The mechanical noise originates from revolving systems connected to the rotors in the form of gearboxes, transmission shafts, transfer gears, auxiliary systems, drive shafts etc.

Future aircraft noise problems

For the fast jets, it is probable ...