FARNBOROUGH Airport’s owners TAG got its sums wrong in calculating the environmental impact of nearly doubling the number of flights there.

The carbon dioxide the flights would create is less than half what TAG believed.

It is predicted that the  50,000 flights that TAG wants would produce nearly two million tonnes of CO2.

This turned out to be wrong because its contractors had accidentally counted the number of engines rather than flights.

Twin-engine planes were counted twice and four-engine planes were counted four times.

The actual figure for 50,000 flights would be 241,153 tonnes of carbon dioxide while cruising.

This is less than what the mistaken calculations said was being created by the flights it had in 2008.

Brandon O’Reilly, the airport’s chief executive, said the exposure of the error was down to the way planning applications are scrutinised.

He said: “People have been going backwards and forwards and query things from Rushmoor Borough Council (since TAG submitted its application in June) and they come back to us.

“In this case it was shown that the emissions the flights would produce was lower by a factor of more than two.

“It’s proof that the planning process is good.”

Mr O’Reilly said the mistake had not prompted TAG to check its calculations on other matters, such as employment projections, noise and the risk of a plane crash.

“We do not believe those contain errors,” he said.

The North East Hampshire branch of the Campaign to Protect Rural England (CPRE) exposed the mistake.

Hugh Sheppard, the branch’s chairman, wrote to Rushmoor Borough Council to say he had compared the projected emissions with those at other airports and they seemed to be up to two and half times higher.

The council put this, along with other questions, to the consultants RPS, which had done the original calculations.

It responded that a “re-evaluation of the figures” had showed the error.

RPS gave new figures, which showed 50,000 flights would create 241,153 tonnes while cruising, less than half of its original calculation of nearly half a million tonnes.

No one at the consultants RPS was available to comment this week.

Mr Sheppard did his own calculations from RPS’s new figures to work out the total CO2 created.

His conclusion was 50,000 flights from the airport would create 977,900 tonnes a year.

This calculation refers to the total CO2 the planes would leave in the entire atmosphere, while the cruising figure only refers to CO2 at ground level.

Mr Sheppard said he now believed the carbon footprint of those flying from Farnborough Airport was 10 times higher than those leaving from Gatwick.

This is because Farnborough Airport’s business jets have far fewer passengers than commercial aircraft.

Like the environmental statement, many include complex calculations about the impact of the proposed expansion on the area, including employment, noise and risk to the public.

Mr O’Reilly added RPS was only involved in calculating the carbon emissions.

Rushmoor Borough Council will now be considering the new figures.

It has yet to set a date to reject or approve the application.

The borough council has changed the rules of the meeting of the planning committee to allow members of the public 90 minutes to speak on the subject.

Ten people will have five minutes each to speak against the proposal.

Representatives from Hart District Council and Surrey Heath Borough Council will also be able to speak for five minutes each.

Thirty minutes would then be available for anyone to speak in favour of it.