DV
I sat on the UK AIRPROX Board for 3 years. Your analysis of Cat A is flawed in my opinion; if you look at risk of collision and RTL then you could argue that every time 2 seperate aircraft get airborne there is a RTL and risk of collision!
Even a Cat A doesn't tell the full story as in most cases the assessment is purely subjective - don't forget the definition of an AIRPROX...
An AIRPROX is a situation in which, in the opinion of a pilot or air traffic services personnel, the distance between aircraft as well as their relative positions and speed have been such that the safety of the aircraft involved may have been compromised. (ICAO Doc 4444: PANS-ATM).
I've added my
bold for reference.
Sometimes a Cat A AIRPROX was not a unanimous vote - so that could also blur the overall picture when a panel of a dozen or so Board members could all have differing opinions.
All said, the UK AIRPROX Board data is useful for an indicator of risk, but needs to be done carefully if it is to support any safety case. In my humble opinion of course.
LJ
PS. Here are the categories (note not classes or classifications):
Risk Ratings
Risk level assessments are made on the basis of what actually took place and not on what may or may not have happened. There are four categories, A - D agreed at international level, and one UK category, E, as follows:
A Risk of Collision: aircraft proximity in which serious risk of collision has existed.
B Safety not assured: aircraft proximity in which the safety of the aircraft may have been compromised.
C No risk of collision: aircraft proximity in which no risk of collision has existed.
D Risk not determined: aircraft proximity in which insufficient information was available to determine the risk involved, or inconclusive or conflicting evidence precluded such determination.
E Met the criteria for reporting but, by analysis, it was determined that normal procedures, safety standards and parameters pertained.