When Hawker-Siddeley upgraded the Trident jet to version 3B they added a few things...5 meters of length, room for 30 passengers, and oh yeah...a fourth engine! (Fourth engine circled in red; intake
Hawker Siddeley Trident 2E G-AVFB (Passenger Cabin) | Flickr
Life on the Trident Fleet - Pilot
Hawker Siddeley Trident - Dumfries Aviation Museum