Citing Department for Transport (DfT) documents, released by the CAA under FOI legislation, The Guardian reports the government expects nearly a million households around Heathrow would experience more daytime noise by 2050 if the runway is built.
This, the data suggests, would impact some 2.2 million people.
In October 2016, the government formally signalled its support for a third runway at Heathrow as opposed to a new runway at Gatwick.
Transport secretary Chris Grayling said despite an increase in flights, the airport had made “firm commitments” to noise reduction.
The government added night noise restrictions would be a requirement of the expansion, as well as legally binding noise targets, quieter planes, a “respite timetable” for those living under the final flight path and £700m to improve noise insulation for residential properties.
The Airport Commission, meanwhile, said even with extra flights, fewer people would be affected by noise from Heathrow from 2030 than are today.
However, Heathrow and the government have since been accused of trying to “conceal” the noise impact of the expansion.
Paul McGuinness, chairman of the No 3rd Runway Coalition, said it had “long been clear” the DfT had understated the numbers, The Guardian reports.
The DfT said a “world-class” compensation and mitigation package, including a £50m annual community fund, would address any noise concerns.
Final proposals for expansion at Heathrow are due in the first half of 2018 ahead of a final parliamentary vote.
The disclosure comes just days after the government published its response to its 2017 “Beyond the horizon: the future of UK aviation” consultation.
It states a new north west runway at Heathrow could generate an additional 260,000 air transport movements per year.
Aviation noise is referenced, with the DfT stating the government is “already acting on aviation noise” through noise controls and the foundation of the Independent Commission on Civil Aviation Noise (ICCAN).
The consultation response also reveals Heathrow’s inbound regional capacity has fallen between 2000 and 2016 due to a high demand for slots, with many domestic routes forced elsewhere to make way for more profitable long-haul routes, as well as competition from other London airports and poor transport links.
The latest Airports National Policy Framework states up to 15% of slots at Heathrow, if expansion goes ahead, should be used for domestic routes.