Thanks, that's clear. Now, why can't they say the same thing on the customer-facing pages instead of only on the agent-facing ones?

Although, as if they wish to reinforce my point about the rules being unclear, they also say that only BA prime flights can be upgraded, when the customer-facing page I quoted above says flights on BA, IB, and AA can be upgraded.

In my opinion, that page which is directed to travel agents is just explaining that travel agents can only use this process for BA prime (no codeshare, no other airline) flights. That BAEC will allow a customer who is a BAEC member to upgrade AA and IB flights directly with BAEC under very restricted conditions is not relevant in that context.

I have never upgraded with avios. if it is done via TA, what booking class is needed for upgrade?

That's fine if they want to only talk about agency bookings there. My point is that they should inform customers what the rules are on the customer-facing page. If they expect agencies to inform customers, then the agency page should also explain the rules. For example, my recollection from the original announcement some years back regarding upgrading AA/IB/BA flights using either Avios or AAdvantage miles is that an agency or airline booking that includes a flight operated by any of the three and marketed by any of the three is eligible to be upgraded either with Avios or AA miles, but I expect only directly with BA or AA. This was some years back, so I could easily be misremembering, and I certainly can't find anything on BA's site that says what the rules are.

Here's the table from the link jerry a. laska posted above:

https://cimg0.ibsrv.net/gimg/www.fly...bfc1423b9f.png

yes. i saw the table. but my question is what booking class does it upgrade to...... U or I from PE to J?

Ah, sorry, I interpreted "needed for the upgrade" as what you needed to be booked into, but you meant what you need to have available. I think it's U for PE to J, and Z for J to F, same as straight awards, but I don't know for certain.

no. i didnt put it out clearly.

for gold upgrade for 2 via TA, PE to J is booked into I class as opposed to U class because TA does not see U space.

therefore, it is interesting to do upgrade via Avios if it can be done via TA as they booked into E/I/A class as opposed to award chart which is a big deal for many people.

Interesting. So you think perhaps J to F would book into A?

On TA-issued ticket using upgrade voucher, buy I FARE (I can be ZERO) book into A directly.
for avios, this is what I want to find out.

For avios upgrades, you still need regular redemption availability in the class to which you are upgrading. This is different than using the GUF vouchers which allow you to upgrade to certain positive cash space fare buckets. So there is no corresponding advantage for using a TA for avios upgrades like there is with GUF upgrades.

Redemption buckets:
https://www.flyertalk.com/forum/29235580-post2.html