A consultant for Coventry Airport said fears by Birmingham International that any shared airspace would affect its growth were "misconceived".
Grant Riddick, who conducted a consultation into airspace capacity problems on behalf of Coventry Airport, was giving evidence during the long-running planning inquiry into its application for a new terminal.
Lawyers for Birmingham International Airport claimed that a proposed expansion would affect it reaching its full capacity of 48 landings and take-offs every hour.
The inquiry, at Leamington Town Hall, heard that each airport disputed the others' modelling for predicted changes to air traffic movements. There were also accusations that each side had withheld information from the other while investigating.
According to a BIA-commissioned report by the National Air Transport Service, and based on predicted WMIA growth by 2014, Coventry's expansion would lead to delays of up to 2.3 minutes per flight at BIA peak times.
But Mr Riddick's report for Coventry Airport - now called West Midlands International Airport - found only two runway configurations would affect sustainable growth at Birmingham International.
Mr Riddick's report quoted the CAA saying it regarded the airspace allocated to Birmingham International Airport as a 'national asset'. It added that the Air Traffic Control Unit at Birmingham International Airport was expected to manage this airspace safely and 'to accommodate all reasonable requests for access including reasonable requests relating to Coventry Airport's air transport, arrival and departure activity'.
'Increased traffic could be safely integrated with the local airspace through local co-ordination,' it said.
"In my view the purported airspace capacity issues raised by Birmingham International Airport are misconceived," stated Mr Riddick.
Coventry Airport hopes to build a permanent terminal capable of handling up to two million passengers a year.
Cross-examining Mr Rid-dick, John Steele, representing BIA, said Coventry had conducted a "wholly clandestine" modelling exercise which had not taken into account modifications they wanted to make.
"It was a wholly clandestine operation was it not?" he asked Mr Riddick. "Why was it nobody was informed about what was going on about this modelling even though we were seeking confirmation with our modelling?" he added.
Mr Riddick countered by saying there had been a "deliberate attempt to withhold information on modelling" by BIA.
Both sides denied the allegations and the hearing continues.