willadvise, thanks for the information you gave in response to Wiley's query. I think most of us can understand how the maths quite correctly gives a theoretical increase in the probability of collision with the wider crossing window that offsetting causes at airways intersections. I can also see that this wider window throws the current formulae you use to calculate clearances for crossing traffic out the window. What I’m trying to get across is that maybe someone at the top should use some lateral thinking and accept that maybe they need to accept these wider tolerances and re-calculate the formulae to allow for a (preferably embedded) offset. Crossing traffic doesn’t scare me nearly as much as opposite direction traffic on the same airway. To hit crossing traffic, you’ve got to be really unlucky in having both aircraft crossing the same three dimensional spot at exactly the same time. With opposite direction traffic, many aircraft occupy exactly the same line in azimuth for up to eight or more hours.
Even if the decision I’ve been asking for was made tomorrow by ICAO, it would still be years before an embedded offset was a part of even one, let alone every FMS in the world. This is why I believe we simply have to allow the manual offset to be made a legal option – and preferably, a requirement – for all aircrew, ASAP. I don’t like the 0.1NM argument put forward by some ATC people. This will not prevent a TCAS Resolution Alert in the event of a mistake - and recent events within my own airline have proven that when surprised pilots receive an unexpected (and in this case, genuine) RA, they sometimes react not exactly as per the TCAS instructions. I want to avoid pilots having to manoeuvre to avoid whenever possible in a TCAS encounter and 0.1NM offset won’t achieve this. Anyone who doesn’t believe me, get clearance from ATC for 1.0NM right of track the next time you have traffic approaching 2000’ above or below you and take a look how close that is. Imagine 0.1NM and you’ll see that it simply isn’t enough.