Class B is not used in Europe, which is probably where your confusion comes from. The starting point in Class B is that ATC is responsible for separating all traffic, including VFR from VFR, so the "type of service" is not really a relevant concept. You must talk to ATC and you must do what they say, regardless of flight rules.
How ATC apply that control to VFR traffic is all there in part 7-9 of the link. I suggest reading the whole part from 7-9-1, including the notes. It's not long and is quite clear, but to summarise:
A) Helos at DCA are VFR in Class B. This means they must squawk and talk (7-9-1) and follow route and altitude clearances given by ATC (7-9-2). This could be a procedural route clearance, but the controller will monitor, separate and sequence by radar (7-9-2a note 2) and may instruct aircraft to hold (7-9-2c). The separation standard is 1.5nm vs large aircraft (7-9-4b1), radar target resolution vs small aircraft (7-9-4d1) or 500ft vertical vs any aircraft (7-9-4b2 and d2).
B) The controller and pilot may agree upon visual separation (7-9-4b3 and d3), in which case the separation minima no longer apply and it becomes the pilot's responsibility to avoid collision. Throughout, traffic advisories must be given (7-9-5) and any vectors given by ATC must meet minimum altitude criteria (7-9-7) which are much higher than 200 feet.
In European terms, my paragraph A) is what you would understand as radar control. The clearance and start of a route through DCA probably reflects your London experience, with a procedural route being followed and the controller keeping airline traffic vertically or horizontally separated by radar. However, as the route gets close to DCA, the separation standards become impossible to achieve. To make progress the pilot must become visual with factor traffic, request visual separation, and be granted it by ATC. If traffic is not sighted then the controller must maintain separation by other means such as holding (vectoring being constrained by the 7-9-7 restrictions at low altitude).
As such, the lateral dimensions of the routes are not very relevant as true "procedural" separation is not used at any point: it's either radar or visual. The maximum heights on Route 4 strike me as a veneer, "safety for show", a paper-thin layer in the Swiss cheese around this accident: a few tens of feet of separation if everything else went wrong. No one can seriously have plotted out the runway 33 approach path and thought that 50ft of separation over the east bank made a valid contribution to a safety case.
The DCA airspace design didn't just incentivise pilots to report visual with traffic and request visual separation: it actively required them to, with no realistic alternative course of action besides holding. In this sort of environment, one can see how pilots might learn to respond reflexively to traffic calls by requesting visual separation to avoid their progress being impeded.
The sort of thing that happens when you don't accept visual separation when required to in Class B is well illustrated by a hotly debated event at SFO a while back. A Lufthansa aircraft refused an ATC request to accept visual separation against parallel approach traffic. Although he reported the traffic in sight, he stated that company policy did not allow him to accept visual separation at night. This left ATC no option for maintaining separation minima besides sending him around and into what some saw as a punishment hold. Lufthansa backed the pilot's decision, but changed their policy as there is no other practical way of operating into some US airports.
Last edited by Easy Street; 18th February 2025 at 20:01.