Let’s start over.
Land area UK : 243,610 km2
Land area US : 9,833,520 km2
Flight hours UK : 22,882.070 over 20 years = 1,144,103 h/year
Flight ours US : 20,896,382 h/year
Density UK : 4.7 h/km2 (per year)
Density US : 2.1 h/km2 (per year)
Density UK vs US = 2.24
According to statistical mechanics, the number of collisions in the UK should be 2.24*2.24 = 5 times that of the US. The numbers show 3.7 times that of the US. The UK is doing better than expected when compared to the US, not worse.
RobertL18C wrote:
Presumably this would be borne out by a statistically meaningful reduction in collisions? Has this been shown?
ADS-B has only been widely in use since 2020, and I think the statistics will take a while to become clear given that mid-air collisions are not frequent events even in the most densely populated airspace such as where I’m based.
As per my post above, my experience leads me to believe that good ATC is useful once in the traffic pattern and ADS-B less so although its still useful, particularly in joining the pattern. Where ADS-B is hugely useful to me is departing and reentering the terminal area where you have large volumes of traffic funneling through specific geographic/airspace created areas to and from 5 or 6 significantly busy airports, mostly without ATC contact or on different approach/airport frequencies. Its is hugely helpful there, I’d estimate that I ‘see’ and avoid five or ten planes on an average local flight that I would be otherwise unaware of.
It is not true BTW that all aircraft in the US radiate ADS-B. However this is virtually true in the specific high density terminal areas of the US where it is mandated for almost everybody.
172driver wrote:
you still don’t get it
Not much flying is Scotland either apparently, a huge chunk of the UK, so I think these things even out pretty much. The activity is pretty much proportional to the population density.
Aircraft density is the only meaningful parameter given everything else is equal, which they pretty much are. If the data were divided into smaller regions, then we could see this more exactly. But the data is given for the entire country. The data as they are given shows a MAC rate in the UK that is lower than expected based on density. Or, the MAC rate in the US is higher than expected. You are free to chose 
172driver wrote:
Basing a MAC comparison on land area is meaningless.
I think that’s correct unless you were to consider only areas above a threshold number of flight hours per year. Even if you don’t and assume both sides of the comparison have a similar concentration of flight hours into a similar fraction of the total land area, in this UK/US comparison the flight hours per unit total land area are 1.9 times as high in the UK, as per my post 16, but the collision rate per hour is about 4 times higher. And no, aircraft collisions don’t obey the same physics as helium atoms randomly moving in a jar.
I would guess the US has a similar or higher concentration of traffic into specific regions, and therefore similar or higher traffic density, but that it has a quarter of the collision rate per flying hour because of better airport ATC where it is necessary and better, more uniform airspace structure/procedures everywhere, including non-tower airports.
Given that there are just slightly more than 100 total mid-air collisions in quedstion, it should be fairly easy to read the reports for all of them and replace speculation with meaningful analysis.
Where would one get both lists?
Let’s remove Alaska, but retain Scotland (and all other low density areas of the UK)
Density UK : 4.7 h/km2 (per year)
Density US : 2.57 h/km2 (per year) Alaska removed
Density UK vs US = 1.83
1.83 * 1.83 = 3.35 This is closer to 3.7 than 5 and a little smaller. This can of course be explained by the fact that since Alaska is large, then the average flight there is also much longer than the average flight around Miami. Anyway, even removing Alaska, but retaining all the flight hours there (which is dishonest at it’s core), and the conclusion is that the UK is still OK compared with the US.
Silvaire wrote:
And no, aircraft collisions don’t obey the same physics as helium atoms randomly moving in a jar.
You know better than that Silvaire. No need to be dishonest to prove a point 
(Again, what point exactly is unclear to me). Helium atoms, cars, snow flakes, planets. It’s pure and simple geometry. The only assumption made is random movement, nothing is done to steer clear of others. The only reason to collide is random movement, because if they knew of each other, they wouldn’t collide, unless deliberately so.
it should be fairly easy to read the reports for all of them and replace speculation with meaningful analysis
+1 or actually make that +1E15
LeSving wrote:
the only assumption made is random movement
Fairly obviously, in a volume of air with a few airports located at defined points all on the ground, fixed and non-uniform physical geography, and fixed and non-uniform airspace structure, aircraft do not move randomly through the volume or collide at random like helium atoms in a jar.
You lot are now going to give me sleepless nights.
UK in 20 years 2003 to 2023 had 39 MAC accidents. That if I am correct is less than 2 a year on average.
USA looks at a 12 year period minus 1 so 11 years and 77 MAC accidents. So 7.7 mid airs per annum.
As someone whose métier was communication with the public I have been thinking how I would present this to a ga sceptical populace. Of course it depends how risky or otherwise I would want them to believe ga was.
I think if I wanted to represent GA to the UK public as no greater risk than say golf, I would present it as less than 2 mid airs a year. Whereas if I was selling ga to the USA public I would present it as 1 every 3million hours of flight. That’s spin and depends on what you are trying to communicate to whom. It’s all about perception.
Please forgive any maths errors, but I hope you still get the point.
