This article is part of our special report Future of aviation: A quieter ride.
SPECIAL REPORT / Though civilian airlines are pressing for quieter, more efficient aircraft, noise output is low on the list of priorities for the sector’s military wing, but there are indications that may be changing.
Noise from civilian aviation is governed by a number of national and European-level rules and international agreements. But military aircraft are exempt from all EU-level legislation, a European Commission spokesman said.
Equally, there is little legislation governing military noise at national level, and little appetite for change. The military has long benefited from special status, its difficult mission to defend public interests affording it a certain lee-way.
Truls Gjestland, a noise researcher at SINTEF, Scandinavia's largest research institute, said: “They do whatever they like. Noise has never been a design criteria for military aircraft. It’s usually power and it’s speed and it’s capability of carrying lots of weapons, missiles. Noise was never an issue.”
But military activity has been an issue for residents near airbases, who complain of disturbed sleep and impacts on their quality of life. According to a study by the Dutch National Institute for Public Health and the Environment, military noise also has an economic cost, with huge impacts on house price depreciation.
The study, “Valuing airport noise in the Netherlands”, rates airport noise as responsible for about €1 billion depreciation in real estate value. Military airbases, it says, account for about 30% of that figure, compared to just 5% for other airports than Amsterdam International Airport Schipol, which alone accounts for 65%.
The authors concluded that “military airbases and flying areas seem to result in more depreciation than civil airports”.
Few studies exist on the impacts of military noise, but there is evidence of adverse health effects. A 2009 study by the World Health Organization (WHO), “Night Noise Guidelines for Europe”, referred to strong links between noise from military aircraft and behavioral awakening in adults. Compared to other noise sources, “military aircraft showed a very strong effect” in disturbing sleep patterns, the study said. But it conceded that the results were of limited applicability as the people polled lived near the end of the runway, where there is most noise.
Gjestland, who is preparing a report on the subject, suggests that military airplanes may affect sleep more than conventional aircraft as they tend to have different flight patterns, such as more nighttime activity – curfews are imposed on the civil sector – and training exercises in the early morning.
Military aircraft also have larger engines and travel faster, creating shorter yet louder bursts of noise, the form which most affects sleep.
Complaints from the public mean that armies are becoming more and more aware of the impacts of their noise on local residents but they concede that some disturbance is inevitable.
A spokesman for the British Ministry of Defence (MOD) told EURACTIV: “The MOD is always mindful of its responsibilities to the general public and treats all flying complaints seriously. It would be preferable if air operations could be conducted without disturbance to those on the ground."
"However, this is not always possible. We have a responsibility to ensure that military aircrews are fully trained and prepared for operational duty, but in meeting this requirement we will continue to do all we can to minimise disturbance.”
The MOD says, however, that it does take the environment into account when choosing its airplanes and also tries to follow as much as possible non-binding guidelines for keeping within civil aviation standards. “When the MOD purchases, or develops, an aircraft a process is followed that provides an environmental features matrix for the evaluation of environmental impact. Noise is a feature of the matrix. Guidance is also provided on how MOD aircraft should, so far as is practicable, comply with ICAO [International Air Certification Organisation] standards.”
But these environmental questions are a secondary concern. “The primary criteria for evaluating which aircraft to purchase are value for money for the taxpayer and operational effectiveness,” the MOD said.
Advances in engineering mean that the armed forces can reconcile more than ever operational effectiveness with low noise output, with urban warfare providing a testing ground for stealth machinery. In 2011, high-tech stealth helicopters burst into the public consciousness as US forces used a low-noise Blackhawk helicopter in the raid on Al Qaeda leader Osama Bin Laden’s compound in Abbottabad, Pakistan.
The picture is different for fighter aircraft, which rely less on stealth than helicopters and land-based vehicles and more on their speed and power to surprise the enemy. Their stealthiness comes more from evading radar detection than a muffled engine, SINTEF's Gjestland said.
But with engineering improvements and tweaks to flight behaviour, the armed forces can even take steps to mitigate the roar of a fighter jet. New models are designed for ever greater maneuverability, allowing pilots to carry out quieter take-offs and landings.
Sebastien Carlsson, a spokesman for Saab Group, told EURACTIV the Swedish aerospace and defence company’s latest fighter, the JAS 39 Gripen, allows for “great flexibility in performing noise abatement maneuvers during take-off and landing." He added: "This is important because peacetime military flight operations can be scheduled and performed in a way that minimises the noise impact on the environment."
Further, the auxiliary power unit (APU) of the Gripen is designed to meet stringent noise levels during ground operations.
While Gjestland greets warmly the engineering changes, he believes that the armed forces will not change their noise behaviour unless they really want to. There may be little appetite for regulation but to the SINTEF researcher the army's main reason for reducing its noise footprint is public relations.
Recent controversial international military campaigns mean its reputation is not what it once was. Gjestland has noticed a change. "Over the last years environmental issues have become more important," he said. "The military depends on good relations to their neighbors, and neighbors are concerned regarding noise," he said. "They want a quiet and peaceful place for themselves and not being waken up during the night. Thus the military tries to reduce the noise impact to their surroundings."
Ultimately, to Gjestland noise is not just about the decibel level but attitude. In his research on civil airports, Gjestland comes up with a noise annoyance level through surveys of local residents. “We do surveys, actually ask people how annoyed are you and they check the noise level and so on.” he said.
The surveys have yielded interesting results.
“The response is not only driven by the noise itself but is very much an attitudinal question,” he said. “If you like what is going on, if you depend on the activity then you have another attitude than if you think this airbase is a nuisance."
"If you don’t like the military you are very annoyed by military noise. But if you work at the airbase, if you have another job, that you deliver goods and services to the airbase, you sort of depend on the airbase being there then you are more tolerant. So this is a very very complex question.”