Mexicana serves MEX, GDL, MLM, and MTY nonstop from SFO. I believe MEX gets 4 daily flights, GDL gets 5, MLM and MTY get one each. All A320s with the occasional 757 sprinkled in on MEX and GDL flights. Both very handsome in the MX colorscheme.
United Airlines serves MEX with one daily nonstop to MEX and several one-stoppers through LAX. The nonstop is an A320 and the one-stoppers originate as Shuttle 737s changing to A320s and A319s out of LAX.
Delta Air Lines once served MEX from SFO, a route inherited from Western. The market was quite lucrative, however DL pulled out of it because it was not in line with the corporate emphasis on East Coast operations. All that now remains of WAL's once-mighty operations to Mexico from SFO and LAX are two flights: DL726, a redeye from LAX to MEX on the 757, and DL427, an afternoon departure to GDL utilizing a 727.
Boy, leave it to me to bring Delta into any topic!
I definitely expect to see AM jump into the SFO market once we see the demise of Cintra. The market is just too big and too profitable not to. I also think we'll see MX get into such profitable markets as DFW and IAH.
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