Originally Posted by silrerelise
I guess that is because "all the evidence" is AAIB reports showing where it hasn't worked. No one logs all the occurences where it has worked. So we just don't know how well it works because we only have the failure statistics not the success ones. Am I making any sense?
Consider two aircraft approaching each other at 120kts each, when the visibility is 6km. The time from the earliest possible sighting to the moment of impact is 50 seconds. We're all taught that the ones that are going to hit you are the hardest to spot, so the distance is likely to be a lot less before the "Mk. 1 eyeball" can identify the danger in the clag. Suppose it took 20 seconds to do a scan, followed by a 10 second VOR position check, and the approaching aircraft was visible at the end, rather than the beginning of the next scan. Did your instinctive reaction, finely honed by regular practice save you, or had the other pilot finished reprogramming his flight plan in time to have already taken avoiding action?
The big sky theory has got to explain why mid-airs are so rare, but stacking the odds with TCAS still appeals.