For me the drop rates decreased on second or third day of the mission. I think completing the mission did not make any change in drop rates from flights & buildings, but the astronauts academy sometimes drops 4 items at once 
Welcome to Airport City!
AirportCityGame.com is the Number One place to be when it comes to the hit game Airport City!
Real time chat to other players, trade items together, complete space missions, form & arrange alliances and much much more. It's all here at AirportCityGame.com
Airport City Game
S3R3G4