local noise = AIAirport.GetNoiseLevelIncrease(tile, a);
local allowed_noise = AITown.GetAllowedNoise(AIAirport.GetNearestTown(tile, a));
if (noise > allowed_noise) continue;

This is how I use it in an AI. Both ScriptAirport::GetNoiseLevelIncrease and ScriptAirport::GetNearestTown call AirportGetNearestTown. I would think a better way was to combine the whole thing and create a new function that does the same but avoids repetition. Something like bool ScriptAirport::IsNoiseLevelAllowed(tile, a).