Draw an ER diagram for an airline reservation system. This system holds information of airports, airplane types, airplanes, flights, flight legs, and seats reserved for a flight leg.

The system handles information such as: 1. In each airport, what kind of airplane type could land, and each airport could land at least one type of airplane. Every airplane has a type. 2. Each flight leg is about from departure airport to arrival airport with scheduled times. 3. Seats are reserved for a flight leg at a certain amount of fare, customers phone number and name should be kept as well. 4. Each flight belongs to an airline company, has several flight legs. Every flight leg belongs to a flight.