Combining FF miles on OneWorld
 

A real basic question, this one. I have flights coming up on Cathay and on BA. Do I have to register for each of their programmes, or is there a single combined One World FF programme, like Star Alliance has Kris Flyer?

You can credit all Oneworld flights to any of the 8 OW member programs. Each program has different features, making it quite hard to determine which is the best program. Often Aadvantage is optimal, but BAEC and CX Asiamiles all have some feature that is best in some conditions. So it depends what fare classes you are flying (they earn differently on each program) and how you want to spend the miles. Usually using more than one program is sub-optimal, until you get into the high end.

Flights will be in Economy, and probably used to get free flights. Does that help point me to the best programme, or at least narrow the field?

Also, can miles be redeemed for flights on any One World carrier, whichever programme I join? eg, can I join AA but redeem on Cathay or BA flights?

No one FF program is really better than another for economy class flights, even though AA is probably the best. Having said that, deep discount economy fares on BA earn little 25% or none (CX) in the AA program. If the flights on CX are in a class that earns miles, that may be the way to go. On BA, you can't even join unless you fly an 'full' fare economy flight.

No, tell a little more about your flying habits. The main question is whether youre in discount economy or full economy, but you also need to tell where youre taking BA (trans-atlantic or other), where youre based out of, and where else you generally travel. There aren't many distinctions other than basic earning and redemption differences when referring to F and J, but economy can lead to some major differences so that your BA flights might earn 100%, 25%, or no percent and your Cathay flights 100% or no percent.

Generally, yes. There are one or two exceptions, most notable not being able to use BA miles on AA US-UK flights or AA on BA US-UK flights.