When considering opening a route to a city with two high demand airports (Tokyo in this case) is the demand calculation specific to the city or the airports listed?
An example: I want to start a route from Singapore to Tokyo (Either Haneda or Narita). I take a look on the destinations list for Singapore and notice that two other airlines currently fly a route out of Haneda to Singapore with relatively large aircraft. There is no direct Singpore-Narita flight. If I start a Singapore-Narita flight will the current traffic out of Haneda impact my ability to fill seats? (assuming I don’t price the flights so high that PAX don’t just ground network to Haneda).
AS demand is airport-based, and the ground connection is very less competitive, so the Haneda really has little impact on Narita flights. That is also the reason if people want to operate in Ibaraki they can’t steal traffic from either Narita or Haneda.
To OP, I’d suggest checking if they fill their flights too, especially if they are decently sized aircraft. And also, how they fill. If there are many connections and such. Though unless you’re the operating carrier you will never know what percent of the specific flight is conx.
It should work, though. Especially in that case.
It might be a bit different if the alternative airport of choice is Panama Albrook vs Panama Tocumen. Where one is clearly where the traffic is. Tokyo is pretty spread out, relatively. Even Chofu and Ibaraki can support supplementals to the key destinations.
I would start with Narita first if there is no competition there. Later add Haneda as well. If the competitors are Japanese carriers and not your partners you are essentially only competing for direct pax with them. The pax originating at Haneda for SE Asia are yours to grab. With long haul flights you will notice that very few passengers are direct.
As previously stated. Demand in AS is airport specific and not city specific. Therefore you need to fly to multiple airports in the same city if you want to collect all the pax.
The basis is for the demand is real (pre covid) airport-to-airport passenger traffic (with some restrictions like charter flights that are excluded).
As you might know this traffic is a bad proxy for the real demand as many passengers travel via a central hub (like Dubai or Atlanta).
Unfortunately there is no data available as far as I know that provides reliable the real passenger airport-to-airport demand
Airlinesim tries to simulate this a bit. To do so the available airport-to-airport traffic is spread with an (unknown) allocation logic to the airports of defined (unknown) regions. This is a try go at least simulate a bit the real passenger demand. Sometimes this works realistic, sometimes not.
What does this mean for your question? It means that you can expect that if one airport is a domestic one and the other international, because of the allocation as just mentioned in airlinesim both airports have international as well domestic direct demand. On top you have the shared demand via ground service.
Especially if you try to build a hub on a smaller airport (in a region with a big/high demand airport) this demand distribution logic might lead to confusion, but also if you have (as in your case) airports with totally different real life destinations the demand in airlinesim might be unexpected