Certainly not all the flights are operated by AA; BA doesn't fly to BHD. Both AA and BA now sell flights operated by the other airline under both codes - AA code on BA metal and vv, so you can buy AA-numbered flights on BA's site, and BA-numbered flights on AA's site, as well as AA-coded BA and BA-coded AA (true "codeshare") flights on both. When redeeming FF miles, however, there are no "codeshare" award flights - the flights always carry the "native" number.

The price differential probably has to do with what fare bucket inventory each airlines has remaining on a given flight. When airlines codeshare, the "operating" airline allows the "selling" airline to have access to X number of seats in each of various fare categories; it's entirely possible AA has sold all its lowest-bucket tickets but BA hasn't (yet) leaving some cheaper seats still for sale by BA. It it's the exact same planes with the exact same routing, then go for the cheapest price. (Be sure to get the booking locator codes for both airlines - they will be different even though it's the same seat.)

If your FF redemption is for any BA-operated flights (and it will be, at least for the flights into BHD) then the $160 savings will likely be eaten by BA fuel surcharges when you get to the final screens on aa.com. You might as a drill just look at flying on AA metal exclusively, BNA-XXX-LHR//CDG-XXX-BNA, and paying cash for the LHR-BHD (or MAN-BHD) segment - it might end up cheaper overall, counting taxes, fees, and BA fuel fines.

Sorry for all the typos above. Still sleepy I guess.

Thanks SO much for the very detailed response. It looks like it would save some money if I booked the Belfast leg from LHR separately. My concern is that if the flight to LHR is delayed -- or if there's a delay getting through customs -- and it's on a completely separate ticket (i.e., with Aer Lingus, which shows the lowest rate) -- they wouldn't be responsible for getting me to my final destination.

It's making my head ache!

That's correct - separate tickets means a no show for the connecting flight will leave you high and dry, so if you want to go that route, give yourself plenty of leeway - probably 3-5 hours if at LHR, 3+ if at MAN. For me, the savings would have to be quite substantial.

I am with you. I was looking at a fare from Sydney to Vietnam with Qantas for $3500. In checking, found it was a codeshare with Vietnam Airlines (not sure of their safety recored) and it was going for $2500.

I haven't decided whether it's worth $160 to fly on the same "metal" with tix issued by different airlines. Still wondering what the disadvantages would be. I'm thinking if there was a cancellation we'd have to go to different counters and deal with different agents and might not get rerouted on the same flights.

But I know the risk of missing a flight (especially in winter) is not worth the savings for me to book separate tix for the different legs.

MissGreen, this is a digression, but I offer some background on Vietnam Airlines, which has served me well three times. It is an efficient and modern operator with a rapidly expanding international network of routes, including Europe. The fleet of more than 60 jets is all late-model. Service to the Americas is said to be on hold until the delayed delivery of its first Boeing Dreamliner. Beyond Qantas, it code-shares with many international carriers including Lufthansa, Cathay Pacific, Air France. It also does maintenance work for some of these airlines on contract. Its last fatalities occurred 20 years ago when it still a local service flying Russian planes, now all long-gone. (Source: Wikipedia.)

While your interim idea to travel on seperate tickets has the potential risks that Gardyloo described, I would not hesitate to fly on two "one tickets" issued by BA and AA respectively.
IF you missed the connecting flight and IF there was not enough space on the next flight to Belfast, preferences should be given by status and fare class and not on which codeshare ticket you travel with.
But that would also be the case if you got the regular ticket from the same airline as your FF ticket.

If things turned sour, I would first go to one desk together in Heathrow, preferably the flight connections desk which you should pass on your way changing gates or terminals anyway, and ask how to make sure that both of you will sit on the same next available plane to Belfast.
If you need to see different airline desks, each of you should also have the booking code and ticket number of the other person's flight with him/her as well. The booking code is a six digit alpha-numeric code on your booking confirmation like BX18IK which can be pulled up by any ticket agent worldwide to check your itinerary.
So each agent can see if and how either of you got re-routed at the other desk.

Thanks Southam for the update. I also figured that if an airline had a dubious safety record Qantas (and other airlines) wouldn't do a codeshare with them.

I did check out their safety record. The list only showed 3 fatalities.

Songdoc, the AA website shows options on your travel date that connect to AA 6714, LHR-BHD, operated by BA.

<the AA website shows options on your travel date that connect to AA 6714, LHR-BHD, operated by BA>

Yes, I see that. But I'm not sure how that affects my concern.

We'll be flying from Nashville to Chicago (O'Hare); and from O'Hare to LHR. My fear (especially with it being winter) is that there would be a problem with the flight from Nashville to Chicago--or the flight from Chicago to Heathrow -- and that being booked through two separate airlines could make it difficult to be rerouted together.

I'm not sure the worry is worth $160 -- but I hate to pay that extra amount for the same flights!!!

My fear (especially with it being winter) is that there would be a problem with the flight from Nashville to Chicago--or the flight from Chicago to Heathrow -- and that being booked through two separate airlines could make it difficult to be rerouted together.

Once you've checked in for the flights, the issuer of the ticket is immaterial; if the BNA-ORD flight is late, you'll both be handled similarly with respect to onward transportation. Codeshare numbering is just a way for airlines to share revenues; in practice it's typically quite invisible from a passenger experience point of view.

In fact, when you go to check in for the BNA-ORD flight, you'll probably be issued boarding passes with AA's PNR locator (booking reference) on all three BPs (BNA-ORD, ORD-LHR, and LHR-BHD) even if the ticket was purchased through BA. The BPs for BNA-ORD and ORD-LHR will probably say something like "Sold as BA XXXX." And when you get to London, you'll probably have to swap the LHR-BHM BP for one issued by BA there, so that it can be read at the gate.

Frankly I think you're over-worrying on this.

>>if the BNA-ORD flight is late, you'll both be handled similarly with respect to onward transportation<<

Meaning, I think (pls correct me if I am wrong, Gardyloo), that both pax would have to deal with the operating carrier leaving from ORD. If it is AA then both of them would get it fixed together, by AA. Same thing at LHR where they would deal with BA.