We've just released (in early beta) our latest feature that allows FlightAware users to view airborne aircraft based on the type of aircraft.
For example: http://flightaware.com/live/aircrafttype/MD83
You can also make wildcard searches on 4-digit aircraft types by using a * (star) as the last character. http://flightaware.com/live/aircrafttype/B73*
Additionally, aircraft types on the airport status pages
are now hyperlinks to the new aircraft type searches.
As always, this is an early beta, there's lots more functionality to come, we hope you enjoy the feature, and please send us any feedback.