We are planning to travel LHR-HKG-BKK and then PER-HKG-LHR in J. We shall be tavelling with our baby and would like him to have his own seat, however I would prefer not to spend Ł3000 to buy it. Can I buy an economy ticket and upgrade with AA miles and if so how many miles?

Before anyone asks he has travelling many times and is very good onboard and does not disturb the cabin.

Thanks.

As far as I know, AA miles cannot be used to upgrade CX flights.

To be more exact, as far as I know, AA miles cannot be used to upgrade on any non-AA flights.

Make it you cannot upgrade on any flight unless it is coded and operated by AA using AA miles. For example, you cannot upgrade on AA coded CX operated flights.

Yup. But apparently I can use Asia Miles to upgrade some AA flights on qualifying fare classes (YBH I think). I guess CX thinks AA miles are somewhat devalued b/c of all the bonuses, etc?

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Yes...I think the math is something like between 2-4 AA miles for every Asiamile

I understand that you cannot upgrade using AA miles, but IIRC, you CAN get award tickets on CX using AA miles, right? Isn't that odd?

Not at all. Most airlines and alliances have dropped cross upgrades using miles.

I know and understand that concept. But it just seems inconsistent that you can value miles from a partner at one level but not at another. It's not really going to affect my life in anyway, I just find it odd... It's like a store in Japan (or HK in this case) saying, "OK, we'll take your US dollars for purchases of candy and gum, but not for milk or coffee." At the end of the day points are a currency, the value of which is determined by the various entities providing services or products in exchange for the points, so taking the same currency for one thing but not the other seems odd. Of course it is clearly stated that the terms of each currency is up to the discretion of these parties, so I know we agree to accept these terms when we sign up, just a funny thing I notieced... Just my two cents.

I agree, I can't really think of a good fundamental reasons why many inter-airline alliances do not let you upgrade on partners. Of course there are exceptions, such as AsiaMiles upgrades on AA, and also CO/NW/KL.

Doesn't AsiaMiles also let you upgrade on BA?

I don't find it odd. Its one of the ways that airlines drive passengers onto their own flights in an alliance that could be competitive on some routes.

You take the currency analogy too far.

in fact, I think Star is indeed pushing more towards the cross-upgrades direction. e.g. I know my LH miles (and in fact also the upgrades from SEN qualification) can be used to upgrade on quite a few airlines.

see this page too:
Star Alliance Upgrade Awards

Yes, according to their website, you can upgrade Y-J on AA in YBH, but on BA, you can upgrade only to the next class of service, e.g. Y to Y+ and Y+ to J. That's the catch on BA. You can't do regular economy to business upgrades.