The 2M Group, an umbrella of local authorities opposed to Heathrow expansion, has called on the Davies Commission to publish its evaluation methodology.
The group led the successful judical challenge to the previous approval of a third runway.
The councils say the only way for the Commission to succeed is for each proposal to be publicly scrutinised against “credible, consistent benchmarks”.
The group insists this process must be completely transparent if affected communities are to have any trust or confidence in the commission’s recommendations.
Leader of Wandsworth Council and 2M spokesman Ravi Govindia said: “The overriding task for the Commission must be to win the confidence of those who will pay the price for any expansion – wherever it is located. It is for these reasons we urge Sir Howard to publish the assessment methodology so this can be opened for public debate.
“Previous Heathrow schemes have fallen by the wayside because the promoters failed to spell out the true environmental, financial and human costs. Without this discipline there can be no confidence that the business case has been properly evaluated and the environmental impacts for local communities fully articulated.”
The 2M Group, named for the combined two million population covered by the authorities, say they are not anti-heathrow, but they remain steadfastly anti-expansion, and want new restrictions on night flights.
Heathrow Airport told the Commission last week that noise could be reduced by changing airspace management, and would in any case reduce through continuing improvements in aviation technology.
Thay also said that extra runway capacity at Heathrow was “the only realistic solution” to the UK’s lack of hub capacity.