That part is the Toei Asakusa Line Airport Ltd. Exp.

Please use hyperdia.com to check for actual trip duration. For example from the schedule below there is 17:05 service from Nihonbashi to Narita Airport. I enter that time into hyperdia and I get the details: train is Toei subway Asakusa Line, turns into Keisei Oshiage Line at Oshiage, turns into Keisei Narita Sky Access at Aoto. There is no need to change train as all the icons shown are double arrow. (http://www.hyperdia.com/help/help_ke.html#point_mark)

If you don't get on that particular train, the next one that comes along in a few minutes will be just a regular metro train.

Weekday Schedule from Nihonbashi: (accessed through http://www.keisei.co.jp/keisei/tetud...ble/index.html )

http://keisei.ekitan.com/naritaacs/T...22-12&d=2&rsf=

And look for these trains that don't need connection (essentially one train per hour)

空 airport

ア特＝アクセス特急
エ快＝エアポート快特