Today’s engines are on average 75% quieter than those produced at the dawn of the jet age, manufacturers say, a result of steady technological improvements that along with more aerodynamic aircraft have reduced the nuisance of flying for passengers and those on the ground.
Yet even if planes are quieter, the surge in air traffic means noise remains a political bombshell in Europe, which leads the world in noise-based flight restrictions. EU states are also obliged to limit noise around airports under a 2002 regulation that is now being revamped to reflect the anticipated growth in the airline industry.
The updated noise regulation, proposed by the European Commission in December 2011, reflect obligations under the International Civil Aviation Organization (ICAO) to create a “balanced approach” to noise pollution, including the use of quieter aircraft, improved airport planning and operational procedures that cut noise levels in the air as well as around airfields.
The aviation industry says it is doing its part through new engine technologies and future airplane designs that will make flying machines quieter than household appliances. Some of the newest aircraft engines coming on the market produce noise equivalent to a food mixer or coffee grinder, or about 85 decibels.
Put another way, “that’s like standing on a busy street corner in Manhattan or London or Paris, whereas the early jet planes were 120 and above – they were rock bands. Rock bands haven’t gotten any quieter but airplanes have,” said Alan H. Epstein, vice president for technology and environment for Pratt & Whitney, an engine manufacturer.
The world’s top engine manufacturers - including Rolls Royce in Europe, and US-based Pratt & Whitney and General Electric - expect business to boom in the years ahead driven by demand for quieter, more fuel-efficient propulsion systems and aircraft.
Boeing forecasts that the number of airplanes in service will double - from 20,310 in 2012 to 41,240 - by 2032. Airbus, Boeing’s chief rival for medium- and long-range passenger jets, also foresees a doubling of the world’s air fleet over 20 years.
Lighter, composite metals have made aircraft themselves more agile and wind resistant - thus quieter as they move through the air. Similarly, jet engines have become more fine-tuned, resulting in less noise and greater fuel efficiency. They have also changed in shape, becoming broader and shorter compared to the tubular jet propulsion systems of the past.
“An airplane needs a certain amount of thrust and you can make the thrust by moving a lot of air slowly, or little bit of air very fast,” Epstein explained in an interview. “The noise gets made by the speed of the air being moved. So from a noise point of view, you want to move as much air as you possible can as slowly as you possibly can. But the inside of the engines – all those compressors and turbines - want to turn really fast.
“In the past we’ve had a compromise between the parts that turned slowly and the parts that want to turn fast because they were all connected just by a shaft. Putting a gear – like the gear on your car - it lets the motor turn fast and the wheels turn at whatever speed they want to go at.”
The next generation
Researchers are already looking to a future that is quieter and more efficient. The American space agency NASA and the EU-financed Clean Sky Initiative have both backed research into aircraft that could replace today’s conventional tube-and-wing designs in the next 20 years. Clean Sky, launched in 2008 with €1.6 billion in funding, is now in its second phase.
Among the futuristic designs that would reduce fuel consumption and noise are aircraft with V-shaped wings blinding into the fuselage, and engines mounted on top of the wings.
“Doing that actually shields the citizen on the ground from rather a lot of the engine noise,” said Andrew Watt, head of environment at Eurocontrol, the Brussels-based civil-military air traffic management and safety organisation.
Eurocontrol is also working to reduce noise through changes in landing patterns, so that aircraft spend less time cruising at lower altitudes before they begin their landing. This gliding approach from higher altitudes reduces fuel consumption and means people living along flight paths endure less noise since aircraft are at higher altitudes.
The EU air control organisation hopes to expand the regular use of what is known as continuous descent operations to more than 200 airports by 2014.
“On the approach, aerodynamic noise is actually quite significant, in particular once you deploy the control surfaces and you deploy the undercarriage,” Watt said. “The aircraft is no longer as clean, as slippery as it was through the air, so that causes turbulence which generates the noise. So often times on the approach, it can be that the dominant factor is the fuselage noise and not that of the engines.”
Demonstrators want restraint
But those living in flight paths may be less convinced that their world is getting quieter.
Protest groups for years have have demanded moratoriums on new runways and terminals at hub airports as well as bans on night passenger and cargo flights.
In May, hundreds of anti-noise demonstrators mixed with travellers at Frankfurt’s airport and earlier this month similar protests were held in Berlin, where the much-delayed Brandenburg Willy Brandt Airport is nearly completion.
Demonstrators opposed to the redevelopment of Istanbul’s Gezi park also called on the Turkish government to reconsider other major public works projects, including what would be the world’s largest airport just outside the city.
In Brussels, airport noise has sparked intercommunal tensions, with the European capital’s French-speaking communities long complaining that they bear the brunt of take-offs and landings to spare Flemish-speaking suburbs close to the airport.
Europe already leads the world in imposing operating restrictions on cargo and passenger operations, limits that are viewed as bad for business in an industry with round-the-clock operations and customers across the world. Of the world’s 161 major airports with night flying limits or bans, 106 are in Europe.
ICAO’s “balance approach” to noise discourages such flying bans, noting that “operating restrictions can have significant economic implications for the airlines concerned, both those based in the states taking action and those based in other states (particularly developing countries) that operate to and from the affected airports.”
Pratt & Whitney’s Epstein acknowledged that aircraft noise would remain politically sensitive even as propulsion grows quieter.
“What the airports decide to do with that lack of noise is a political question – it can be longer flight hours, it can be more flights per day … or it could be reducing the noise for the community,” he said in a telephone interview. “It’s a questions that will generate a lot of press because it has no unique technical answer. It’s a political-economic answer and I suspect the optimum is different for different communities.”