Alpha_Floor wrote:
Lack of data does NOT mean that both approaches are equally safe in principle
Hmm. Lots of implicit factors here. What is “safe” anyway, except a calculated risk based on data? What is data, except the number of accident events vs the number of non accident events? What I mean is that logic is no measure for safety, only data is. Thus, the semi circular rule works just fine. There is no lack of data, only “lack” of accidental events, which again is the basis if the fact that the rule is safe, based on data. The data shows that mid airs en route is extremely rare. The data also shows that all other rules are safe (flying below 3000 AGL where the rule doesn’t apply is also safe)
Malibuflyer wrote:
The difference is: the first half of your statement is based on facts while the second half is based on theory.
I see your point, but would hold up the AAIB statistics for the UK (where random altitudes are encouraged), and these statistics show no increased risk either, so not completely theoretical.
Malibuflyer wrote:
I rather argue that we should not try to fix something that is obviously not broken.
In the end it seems it does not really matter, doesn’t it. From the discussion I gather that a lot of traffic seems to fly below the required semi-circular altitude anyway, IFR tends to fly higher than the usual VFR cruising altitudes, so yes, nothing needs to be changed.
Sebastian_H wrote:
Isn’t that a bit fallacious? … So of course flying semi-circularly is safe as there are no accidents, but so is equally flying at random altitudes.
The difference is: the first half of your statement is based on facts while the second half is based on theory.
I do not want to argue that flying random altitudes can’t be as safe as semi circular altitudes (as explained: can not be better as semi circular is already perfectly safe). I rather argue that we should not try to fix something that is obviously not broken.
Malibuflyer wrote:
The current practice of flying semi circular altitudes is extremely safe
Isn’t that a bit fallacious? I would state it more as “it does not matter if or if not you comply with the semi-circular rule” since there are hardly any mid-airs. So of course flying semi-circularly is safe as there are no accidents, but so is equally flying at random altitudes. The correlation between accidents and semi-circular or not is as good as the correlation between accidents and colour of underwear :)
Alpha_Floor wrote:
Lack of data does NOT mean that both approaches are equally safe in principle, saying that is a logical fallacy…
But we do have data, don’t we? Running quickly through the AAIB and BEA reports, I found from the AAIB the latest mid-air report occurred in June 2019 and nothing for 2020 or 2019 from the BEA. There’s an old report from BEA on mid-air occurrences that has 1.7 mid-airs per year in the interval 1989-1999. Since we hardly seem to have any mid-air collisions at all anyway, a statement “behaviour X causes more mid-airs than behaviour Y” simply has no basis.
Peter wrote:
I would suggest that the reason it makes little difference to mid-airs is because most GA happens at levels which are too low to be applicable to semicircular numbers.
I’d rather suggest that the reason is that enroute mid airs in GA are an extremely rare event – so there is simply only very little difference to make even if something could eliminate enroute midairs completely.
Alpha_Floor wrote:
Lack of data does NOT mean that both approaches are equally safe in principle, saying that is a logical fallacy…
Right! But it does mean, that it simply doesn’t matter which of the two approaches is safer in principle because there is not much you can improve.
The current practice of flying semi circular altitudes is extremely safe (in the ballpark of less than one accident in Europe every 10 years). In the absence of good data, why risk this extreme level of safety we already established by changing the rules that perhaps theoretically could improve this safety a bit at the risk of lowering it significantly.
Or to put it simpler: There is much more to loose by changing semicircular rules than to win.
Lack of data does NOT mean that both approaches are equally safe in principle, saying that is a logical fallacy…
I would suggest that the reason it makes little difference to mid-airs is because most GA happens at levels which are too low to be applicable to semicircular numbers.
For example, in the UK, the vast majority of traffic is at/below 2000ft. And nearly all traffic I have seen in France was also very low down.
Exactly. The topic tends to get people worked up. But in the end, as with many other things in GA, there is no data; no science to prove which is safer than the other, even though many think they know it.
gallois wrote:
But as has been stated this is perfectly legal in the UK it is not in France so perhaps we feel safer with what we know.
Since there seems to be no increased en-route occurrences of mid-air collisions in the UK vs France, I would wager that neither procedure is safer than the other …
