This thread is about the littlest of things. Curiosity has the best of me as I board yet another flight.

Certainly, there is some logic to CX's flight numbers that I've figured out. For example, Australia and New Zealand flights are in the 100's. Europe flights inc appear previously to be all 200's, until Manchester and Zurich came along (and Dusseldorf comes along), which are the only European flights in the 300's. So MAN, ZRH and DUS are lumped alongside PVG and PEK, which are the only 300's I can think of and something of an odd lot. Some Taiwan and Korea are 400's, Japan and remaining Taiwan flights are the 500's, Indian subcontinent + Maldives + some Middle East are the 600's, remaining Middle East + SE Asia (ex Philippines) + JNB lumped in are the 700s, North America flights are 800's, Philippines flights are 900's.

So there is some logic, and also some exceptions. Curious about why, for example CX is now using the 300's for additional Europe flights when there are so many open #s in the 200's? Of course, there appears some attempt at keeping the "10"'s place open for a specific city (or perhaps country?), like AMS is 270/271, FCO is 292/293, etc. But, even this logic doesn't perfectly follow...eg MXP is 232/233, whereas a few LHR flights are also 23X (238 and 239 I believe?). Why is Europe now 300's?

And I'm curious why the new SFO flight got 892/893, instead of 874/875 876/877? (the legacy SFO flight #s are 870, 872, 873 and 879).

Same question about LAX as well, why the newest LAX flight got 898/897? While the old flight #s were 880, 881, 882, 883, 884 and 885, with 886 and 887. Why not use those?

Being honest, this isn't really not relevant to a whole lot...except my curiosity!

With CX's expansion, particularly with the intro of the A350s, I have to imagine it won't be too long before whatever logic there was goes out the window, unless there is some type of rejuggling of the flight #s. Any thoughts welcome.

238/239 were 'inherited' from NZ38/39 I think

I thought I had read here on FT that there can be issues sometimes with ATC when new routes start -- the authorities can weigh in on flight numbering to avoid similar numbers on different carriers operating in the same airports at the same time. No idea if that would explain some of the exceptions you point out.

Pick random numbers out of a hat, put the numbers in any random order, there's one flight number. Add one or subtract one and you got the reverse.

Correct, authorities will review them and will discourage numbers that are similar, like (hypothetically) CX899 with CI899, usually they will do their best to ensure enough diversities. Thought a major airport like JFK I would imagine it will be very hard.

The numbers may be similar at high volume airports but I don't believe the iata codes and the numbers are similar both together at any given airport route. Plus they should be using NATO alphabet. Charlie x ray 899 vs Charlie India 899.

You probably meant ICAO codes not IATA codes. ICAO codes are three letters. CX - CPA.

ATC does not read out the two digit IATA airline code in their communications. Instead they use an airline's call sign: Cathay for CX, Dynasty for CI, for example. Others include: American for AA, Speedbird for BA, etc.

That's exactly the reason. Most European flights depart within 1-2 hours before/after midnight, while for the North American flights, they depart at different time in a day. It is unlikely that two (or more) flights with similar flight numbers (and hence call sign) are flying at the same time. CAD Hong Kong has guidelines on this (published in AIP).