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The simplest means to clarify how they work is comparing the same information seen through the naked eye and the two scopes. This is the scenario we will be using, with our trusted F-14 Tomcat since it displays both types of scopes at the same time.
This is the Marianas map, and we will be flying through the narrow corridor between Saipan and Tinian, maintaining the latter on our right-hand side. By means of the DDD in Pulse mode, we will be seeing the two islands passing to our sides, whist two Steerpoints located at the tips of the islands, will allow us to follow the flight from the PPI point of view. The perspective from the Radar Intercept Officer is also shown, allowing you to correlate the whole view and, hopefully, understand how the scopes portray the information you see.
What will happen is rather simple: the B-scope shows the radar’s perspective, which is kind of similar to the human eye, if we do not considered the different azimuth. Therefore, as an object gets closer, it will move towards the sides. The Plan Position Indicator, instead, is a sort of “god’s eye view” with some caveats and, for this reason, the relative position of the steerpoints will remain unchanged.
Small coloured indicators will also mark the where the scopes show the same information, with a certain degree of approximation.
As we have seen, the islands tend to “Drift” towards the edge of the B-scope. PPI is a top-down projection instead.
Therefore, another way to explain the B-Scope is imagining a corridor with a piece of furniture on the other side. As you walk towards it, it tends to move from the centre of your view, to a side. Eventually, it disappears from your field of view. Also, the closer you get, the quicker it drifts.
By the way, if the furniture did not drift, you have probably hit it by now. The reason is that your knee and the piece of furniture were on a Collision Course. Now go and put some ice on it!
There are other differences between these scopes, but this is the most basic. I hope this article has been useful, as this is one of the most important parts of the avionics for any crew member.
FlyAndWire 