American AAdvantage has many airline partners, both in oneworld and not in oneworld. One of the nice things is that as long as the other award rules are met, you can generally mix and match airlines on a single award as much as your heart desires.

There are of course some restrictions, and per JonNYC at TravelingBetter, it looks like American has added a restriction for AAdvantage awards on Hawaiian Airlines:
Itineraries to/from Central, South America or Transatlantic that include Hawaiian Airlines (HA)will not price as one award and are only valid if multiple award(s) are claimed.
This is a new rule as far as I know, and means that you can no longer fly Hawaiian Airlines as part of a mixed carrier award between Hawaii and either Central America, South America, or Europe.
Let me explain what this means in practice. Say you want to fly from London to Honolulu, and you choose to connect in Los Angeles.
Previously you could fly London to Los Angeles on American or British Airways and then Los Angeles to Honolulu on Hawaiian Airlines on a single one-way award.
Unfortunately now that will cost you extra, and you’ll be charged separately for the London to Los Angeles and Los Angeles to Honolulu segments.
Take a look at the below flights, for example. American shows award space from London to Los Angeles on British Airways and then Los Angeles to Honolulu on American:

However, when you search separately there’s actually an earlier connection from Los Angeles to Honolulu on Hawaiian Airlines:

That flight won’t automatically display, and if you “force” those two segments together using the multi-city tool, it prices them cumulatively, at 42,500 AAdvantage miles one-way, rather than 20,000 miles.
Bottom line
It’s just another restriction to be aware of, though certainly not the end of the world. This would have been a much bigger deal back in the day when American allowed a free stopovers at the North American gateway city. At the time you could fly London to Los Angeles, stop for as long as you wanted (well, within the year-long ticket validity), and then continue to Hawaii at no extra cost. Since they discontinued that benefit, I don’t think this is quite as much of a loss. It’s still definitely bad news for those that frequently travel longhaul to/from Hawaii.
I’m curious what prompted this change in policy…
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