The airbrakes were extended on all normal approaches to land because as PN stated the engines would then be in a higher (more responsive) setting (with the gear down the airbrakes moved to a higher drag position than with the gear up.) Note: the Vulcan has no flaps which solved the problem on ' conventional ' ac . Also with airbrakes out the nose was lower which gave the pilot a much better 'view' of the runway.
Occasionally approaches were practiced airbrakeless - these were quite tricky as it was very difficult to control the speed without reducing power to a low (irresponsive) setting. Also as the ac nose was unusually high on landing airbrakeless this meant that you had to be careful not to 'round out' too much which could result in a long 'float' and possibly a 'tail scrape' not to mention losing good sight of the runway!
Obviously the airbrakes would be IN for T/O and selected IN on rollers - which was probably happening in this case??