West Sussex County Council has withdrawn its support for a second runway at London Gatwick airport.
Following widespread local opposition, the council voted 37 to 26 to reverse its July 2013 decision to support expansion at the airport.
The move follows Kent County Council withdrawing its own backing for a second runway in November. That decision was made due to new flight paths.
How the proposed second runway at Gatwick would look
The Airports Commission has three options for airport expansion in the south-east — a third runway at Heathrow, extending an existing runway at Heathrow, or a second runway at Gatwick.
London mayor Boris Johnson's plans for a new airport in the Thames estuary were dismissed by the commission last year (see news, September 2).
West Sussex County Council councillor Pieter Montyn said: "The issue of a second runway at Gatwick is an extremely emotive subject.
"Councillors believed that Gatwick has not, to date, put forward sufficient evidence to counter the very serious environmental and noise fears of local residents.
"However, irrespective of our position, our role now is to start planning for the future. The decision about the runway will be made by government so we have a responsibility and duty to plan for either scenario - second runway at Gatwick or not."
A spokesman for Gatwick airport said: "While obviously disappointed at this decision, we will continue to work closely with West Sussex County Council to illustrate the benefits, both economic and social, that expansion will deliver for years to come.
"Gatwick is doing as much as possible to reduce the impact of aircraft noise on local residents. If chosen for expansion, we will work with local authorities to maximise the benefit and minimise, mitigate against, or compensate for, the impacts of a second runway."