Is my ERD valid for airports,cities and airlines database? My objective is to make a database of airports, cities and the airlines which provide coverage to them. 

I asked the question before on stackoverflow and the person told me to break up the many-to-many relationship between airport and airline(I  agree with that). Moreover, he/she raised objection on relationship between airline and country.

I thought an airline belongs to a country so i made a relationship between two. Kindly, give your suggestions on the ERD and how i can improve it?
Looks ok.

Some countries span multiple continents, such as Russia and Turkey.

Some airports might not be in cities, like Mirabel (YMX), which is 53k from Montreal.