An airport transit visa is valid only for transiting through the international transit areas of the airports situated on the territory of the Member States. It can include an additional “period of grace” granted by the Member States for reasons of public policy or other specific reasons. The maximum duration on an airport transit visa is 6 months. This type of visa is mostly for third-countries nationals who are passing through the international transit areas of airports situated on the territory of the Schengen countries.
You might have to fill a Schengen Visa Application for a regular Schengen Visa (C type) if you have to leave the airport to take your flight in another airport for example.
Immigration And Migration 