Commonsense? Hardly. It is well thought out rules that keep things safe, the only problem seems to be when they are not obeyed or understood.
Very true. Although courtesy (not to mention self preservation) means aircraft joining a circuit pattern tend to give way to those already in it I can, which surprised me, find no Rule that actually states that Circuit Traffic has any specific right of way.
All Quotes from CAP393
Avoiding aerial collisions
8 (5) Subject to sub-paragraph (7), an aircraft which has the right-of-way under this rule shall maintain its course and speed.
Since a pilot certainly wants to do this when concentrating on landing it is no surprise that:
Order of landing
13 (1) An aircraft landing or on its final approach to land shall have the right-of-way over other aircraft in flight or on the ground or water.
(2) An aircraft shall not overtake or cut in front of another aircraft on its final approach to land.
Flight in the vicinity of an aerodrome
12 (1) …a flying machine flying in the vicinity of … an aerodrome shall:
(a) conform to the pattern of traffic formed by other aircraft intending to land at that Aerodrome ….
A single pattern allows for an orderly single flow of Aircraft on to a final approach (0 to 4 nm from Threshold so ATZ, or not, is irrelevent) ie no multiple Base Legs, a variety of distances out from the threshold, which could be interesting, if not chaotic. However,
due to 13, all aircraft are still required to give way to aircraft already on Final - no matter how they got there.
Converging
9 (3) Subject to paragraphs (1) and (2), when two aircraft are converging in the air at approximately the same altitude, the aircraft which has the other on its right shall give way.
The above means that an aircraft joining a L/H Circuit Crosswind would be required to give way to existing Downwind Traffic.
But what about an aircraft that has Gone Around and is now flying along the runway at circuit height? The Rules state they are the ones who must now give way to an aircraft joining from the Deadside.
What about a R/H Circuit?
Pilots flying a Straight In approach to an airfield with a busy circuit pattern may not be popular but that does not mean they do not have right of way.