werido_salt good comment but although there is an element of risk involved in the fly-by, the airline would also realise that it is a free promotion of the airline, the thousands of people at the airshow and indeed on youtube see an exciting well performed piece of flying so therefore think of the airline as having good aircraft operated by well trained, skilled crews. And therefore they fly that airline because at the end of the day no matter how cheap the ticket if the airline flys old aircraft that fail often with poorly skilled pilots they don't fly with them.