The question pre-judges that the solution is actually an aeroplane - there's no particular reason why it has to be and artificially constraining the options too early in the process is rarely a good idea.
For example a requirement that calls for “a bridge capable of handling 500 cars per hour in each direction” would allow bidders to offer a suspension bridge, a box-girder bridge, a pontoon bridge or indeed any of many other technical approaches, but all of them must be bridges.
A requirement calling for a “river crossing capability for 500 cars per hour in each direction” would allow all of these, or a tunnel, or a ferry service, or a catapult-and-net system. It might even allow an enterprising contractor to offer a service-based solution using a fleet of surplus heavy-lift helicopters that he happened to see coming up on Ebay with 1 minute to go, no bids and a £0.99 minimum bid price. That could achieve the requirement with a totally different financial profile (minimal capital, higher revenue) whilst also adding the benefit that it could be in operation in a matter of weeks with no construction disruption rather than needing five years of construction investment and constipating of local traffic for the duration.
Focus on the mission first - never prejudge a solution. Some maritime patrol requirements can be fulfilled with remote video camera with a zoom lens. That solution wouldn't need a galley or a toilet...
PDR