Originally Posted by
aerokitty
Looking at SFO-PEN. United.com routes SFO-SIN-PEN, but uses 3K for SIN-PEN instead of MI. True, MI is not *A but is at least aligned with SQ while 3K is owned by QF and hence aligned with OW. Seems odd -- MI seems to have reasonable baggage allowances. I hae no idea what 3K would offer.
Same reason that SQ codeshares mostly with VX for its domestic US traffic. UA and SQ just don't get along at all.