The Economist's Gulliver blog points out something opponents to Heathrow's third runway may have missed:
In Britain the long-awaited Davies Commission report on a third runway for London is set for release shortly. The main objections to new runways by locals is the additional noise they will suffer. But by the time any new runway gets built in a decade or more, much of the fleet serving London will have been replaced by these new planes that whisper rather than roar. Describing volume is tricky but Bombardier’s new CSeries, a small single-aisle short-haul jet, equipped with Pratt & Whitney’s geared turbofan engine, was barely audible at times during its flight at just a few hundred yards from the watching crowds. Boeing’s 787 Dreamliner (pictured) and even Airbus’s A350 and A380 also made far less noise than would seem possible. Critics will point out that the planemakers do their utmost to make these display particularly silent, nevertheless the results are astonishing.
The noise reduction from new technology is significant. In early jet engines, which were ear-splitting, all of the air was forced through the engine core in which combustion takes place. High bypass systems, with some of the air directed around the engine core, made engines quieter and more fuel efficient. The engine on the CSeries uses a gear, allowing the front fan to turn at a lower speed than the engine core, reducing noise further. The CSeries, 787 and A350, constructed from composite materials, are lighter than their predecessors too, which helps keep noise down.
My new place is directly under the approach path to O'Hare's runway 28C, which opened in October 2013. Residents along this flight path worried that the runway would generate tons of noise. As it turned out, it really didn't, principally because of these new technologies. (Also because landing airplanes make much less noise than departing airplanes.) Someday, I hope London gets another runway, and I hope that people realise sooner rather than later that it won't be nearly as bad as they fear.