Originally Posted by
aacharya
Simple answer:
Whichever airline you are beginning with at each end.
Harder answer:
The Most Significant Carrier (IATA 302 and the DOT regulation)
I would imagine LHR to MAA is less lengthy than SFO-LHR, and hence UA is the MSC.
SFO-FRA 5699, FRA-MAA abt 4700, so yes, but not "by much". I'd print the web page and be prepared to debate this with MAA agents, as the LH outsourced staff can be quite difficult on this issue, I had quite the debate with them in more than one station when it came to checking bags.