Safety is paramount in aviation. Prevention and protection measures against life threatening situations are well known and are taken extremely serious by everyone. Protection against less noticeable, but in the long-term comfort threatening situations, however, receive much less attention from the individual. This is not different in the military in general, and in military aviation in particular. No fast jet pilot will take-off in an aircraft without a well-maintained and functional ejection seat or will enter a combat zone without the proper countermeasures against anti-aircraft weapon systems. Working near aircraft with running engines without the proper ear protection, however, happens quite regularly. For that reason, the Belgian Defence set-up a number of preventive actions to sensitise its personnel to take the proper precautions against such insidious threats.

The noise level in the cockpit of a Sea King is around 95 decibels. In that of an A.109BA helicopter or a C-130H transport aircraft it is even higher and reaches 104 decibels. A traditional flying helmet reduces these noise levels only to 84 and 90 decibels respectively, still well over the noise limits permitted by the new regulation on the matter in vigour since 16 February 2006. To offer his pilots the proper protection, the Assistant Chief of Staff for Well-being (ACOS WB) started to provide them with special communication earplugs (CEPs). When wearing CEPs, the noise level is reduced to a much more comfortable 55 decibels in the cockpit of the Sea King and to 58 decibels in that of the Hirundo or Hercules. Continuous exposure to these reduced noise levels will not entail any hearing damage, not even after flights of as long as 8 hours. The communications earplugs reduce loud background noise levels by around 30 decibels and in the meantime improve the audibility of radio communications by built-in micro-loudspeakers. The Belgian Air Component is one of the forerunners in the application of this technology as all Belgian military pilots already received their pair of CEPs, while other air forces, such as those of the United States and Switzerland, only started distributing these protective devices this year.

 For ground crews working in the vicinity of aircraft with running engines, the danger of permanent damage to the ear is even greater. At a distance of 10 meters in front of an F-16, a crew chief is exposed to noise levels of as high as 115 decibels, causing hearing damage after only a few seconds. This is why the new royal decree only allows unprotected exposure to such noise levels during 11 seconds, which is far less than the time needed to get an aircraft airborne safely. Ground crews therefore are provided with ear caps or earplugs. Careful attention, however, has to be given to the choice of the proper caps or plugs, as two different types do exist. One type only protects against pulsating noise like that of gunfire. The other protects against continuous noise like that of aircraft engines.

 The pulsating noise of guns and cannons can be effectively reduced with non-linear earplugs or electronic ear caps. Non-linear earplugs are simple and cheap and basically function like the exhaust silencer on a car. They, however, do not reduce continuous noise or low energy sound waves. This means that they are not to be used for ear protection on airfields, but on shooting ranges, where they stop all gunfire noises, without hampering oral communication. Electronic ear caps have two built-in microphones and work on the principle of anti-noise. They are sophisticated, expensive and work on batteries. A study carried out by the Department of Audiology of the University of Ghent on behalf of the Ministry of Defence, revealed that the cheap non-linear earplugs are as effective as the expensive electronic ear caps if they are inserted properly into the ear.

 Continuous noise can be reduced with traditional ear caps or earplugs, both very common and cheap items. So, next time when you visit an air show or open house and you are in the vicinity of an aircraft being prepared for a flight, be sure to wear the proper earplugs. Never wear the mushroom like linear earplugs, because they will not protect against deafening jet noise. Only use the well-known yellow cylinder-shaped foam rubber plugs or the somewhat more sophisticated plastic plugs with successive noise muffling lamellae. This simple gesture will let you enjoy the sound of freedom of our military aircraft for many more years…

 

 2nd Lt Renaud “Grat” Thys shows how a fast jet pilot protects his ears against hearing damage: (1) he inserts the communication earplugs in his ears, (2) then puts on his flying helmet and (3) finally plugs in the cable of the micro-loudspeakers in the socket at the right-hand backside of the helmet.

 

 Aviation enthusiast too should wear the proper protective earplugs in the vicinity of aircraft. The ones in the middle and on the left are suitable, those on the right are not. The latter are non-linear earplugs and only abate the noise of pulsating sources like gunfire.