An aviation expert has cast doubt on the predicted passenger growth at Birmingham international Airport on which the hub is basing its billion-pound expansion plans.
Proposals for a runway extension and a new second runway at BIA are based on a predicted trebling of demand - to 33 million passengers per year - by 2030.
However, speaking at the public inquiry into Coventry Airport's development plans, traffic forecasting specialist Peter Hind said: "I have always been of the opinion it is difficult to predict with any certainty how an airport will grow beyond ten years."
BIA objects to the development of a terminal handling two million passengers per year at Coventry because it believes airspace constraints between the two airports - just 11 miles apart - will compromise its £1.5 billion growth Master Plan.
Mr Hind, who was called to appear before the inquiry at Leamington Town Hall as a witness on behalf of CA, also predicted the airport would be marketed aggressively as a facility for small private business jets if the passenger terminal was not granted.
This would result in four times more aircraft - executive jets and air taxis - using the airport annually by 2030.
His report concludes that if the new permanent terminal is granted planning permission by the Secretary of State following the inquiry, it will reach 1.96 million passengers per year by 2014, with as many as 46 planes either landing or taking off every day in the summer peak.
He added that by 2030, air traffic would remain much the same because CA has committed to cap its business at two million passengers per year.
John Steel QC, on behalf of BIA, described Mr Hind's report as "unrealistic" because it assumed the current Thomsonfly low-cost operation at Coventry would remain the same over the next eight years.
He said there were no guarantees that operators would use bigger planes to meet demand.
Mr Steel said it was known that CA was actively seeking to attract new airlines to the airport and added some low-cost operators currently used fleets of smaller planes.
He told Mr Hind: "What you cannot say is what that throughput of passengers will amount to in terms of air traffic movements.
"You cannot say what the mix will be.
"The number of air traffic movements could change per season and also the destinations served could change."
The inquiry is due to last until the end of February.