When using the Gatwick Airport Air Bridge on several occasions we have seen pilots wave back to PAX (usually children) who have stopped to watch aircraft which are taxiing and about to pass underneath the bridge.
http://simflight.com/wp-content/uplo.../Airbridge.jpg
Our grandson is a keen aircraft spotter and loves to go over the giant bridge.
We are not so keen due to the distance to walk to the North Terminal, especially last time when the escalators were out of action !