One participates within a Thread.
Current system seems fine to me....you want something to do specifically with Helicopters....go to Rotorheads. If one is interested in the topic within a Thread....pitch in!
I look at Rotorheads Forum as being the center of the Universe for all things Helicopter. The Industry needs to come together as a whole if we are to progress as a trade, profession, and collegial group of people.
I would vote to keep things as they are.....otherwise the tendency would be to skip over several sub-forums as one assumes there is little of current personal interest to be found.
Now...you do get the benefit of seeing all the Active Threads within the Rotorheads Forum as you scroll down through the Threads thus you might trip into what might be a missed topic if you did not enter that particular sub-forum.
In a left handed way that encourages people to read things they might not normally do...and perhaps get a bit of vicarious cross training which cannot hurt anyone.