Airports and noise limit
An important thing to note is the noise limit of a city. This can be seen in the town window and represents what size airport you can build right next to the city. An increased distance from the city decreases the amount of noise produced, so theoretically you can build an airport with a higher noise rating than the towns noise limit, it just needs to be built further from the town.
Sometimes, due to noise levels restrictions, players build small airports and use big planes. That is not right as there is a 5% risk of a crash for big airplanes that land on short airstrips. You will lose passengers, rating and money to buy a new plane. Small airplanes are recommended for this type of airport. In the expanded color menu you can choose separate colors for small and big airplanes for easier understanding of which is which.