wrote:

Finally note that British Airways is not a US carrier and not even
required to
follow 14 CFR 121.

Untrue.
121.1
This part prescribes rules governing--
...
(f) Each person who is an applicant for an Air Carrier Certificate or
an Operating Certificate under part 119 of this chapter, when
conducting proving tests.

British Airways is no such applicant, nor is any other foreign flagged
carrier.

119.1(a) This part applies to each person operating or intending to
operate civil aircraft -
(1) As an air carrier or commercial operator, or both, in air
commerce;

It's nice to be able to quote selected portions of the CFR. It's more
important to have a clue what you are quoting. Before claiming that part
119 refers to foreign flagged airlines operating in the USA, you might be
interested in reading part 119. See 14 CFR 119.1 (d)

So if they want to operate as an air carrier in the U.S. then for the
portion of their flight in U.S. territory they are indeed subject to 14
CFR 121.

Absolutely False.