IL18-A Cannot Assign to Route Even Though No Restrictions

Game: History and the Future

Player: JJP

Airline: Avalon Air

Route: LAX to EYW

Issue: When editing / creating the route, game says there are no payload or runway restrictions for IL18-A to fly this route.  However, when I attempt to assign the route to such an aircraft, I receive the message: "You cannot assign this route to this aircraft. The aircraft is unable to fly any payload to this distance due to runway lengths and payload/range capability."  This should only be true of the IL18-B which I do not have.