Offset Pursuit
This behaviour is very useful if vehicles are supposed to move in
formation e.g. Red Arrows aerobatic display. 
In this example the planes all have their own offset position (yellow) relative to the lead plane (red). The lead plane will be using its own steering behaviour. For each of the 'pursuing' planes their expected world position is calculated from the lead plane's position and the offset. The steering force is calculated using the arrive behaviour with the expected position.
Offset pursuit is used in the City Patrol sketch to keep the patrol members in position on their leader, while the leader is using path following behaviour to navigate the city.