Cornwall County Council has refused to publish information about the economic impact of Newquay Airport.
A meeting of the Federation of Small Businesses was told passengers figures would reach 1.7m by 2020.
But Councillor Andrew Mitchell, economy portfolio holder, refused to reveal the results of a survey into the economic impact of the airport on the county.
Mr Mitchell said some research was not satisfactory, but he was confident in the passenger predictions.
At the meeting of small businesses on Tuesday night, Cllr Mitchell said the survey was being done again because he felt the figures could be better.
He said: "The results were encouraging, but it think they did undervalue the impact the airport has on the Cornish economy."
When asked why he was accepting the figures about passenger numbers and not those about economic impact, he said: "I believe those feel right.
"Industry experts and government advisers at the Department for Transport have signed of on those and believe they are achievable, so I have accepted those."
Some businessmen said they were unimpressed by the councillor's use of one set of figures but not others.
Richard King, of Trading Pages in Camborne, said: "When you are playing with tax-payer's money, I don't see how you can live on a wing and prayer like that."
Cllr Mitchell said: "The county council is not the only body that signed up to and has paid for that research. Once all the partners on board are happy, we will make those figures public."
The airport currently handles about 350,000 passengers a year.
The first stage of a £2.8m expansion of the arrivals terminal at the airport started at the beginning of March.