According to Airlines Reporting Corporation, prices for flights are generally cheapest around 6 weeks prior to the date of the flight. While, this study applies to US flights, I think it’s generally true for Hong Kong to long-haul destinations as well, (for non-holiday periods.)
My logic is that airlines will generally set their prices well in advance at a fairly high price, to see who buys tickets. Then when it gets closer to the travel date, when airlines see the planes are empty, they’ll lower prices to make sure the planes don’t fly empty. This appears about 2 mos – 6 weeks prior. At that point, if consumers buy the cheaper tickets, the airlines will raise their price back up again closer to travel date. If consumers don’t bite, they’ll probably keep the prices at the same level or may even lower them further.
But with capacity so tight these days, I am seeing that airlines are not that aggressive with pricing, and would rather force you to pay the higher prices by not having as many fare wars. Sometimes it’s also tough to wait until 6 weeks prior, when you have very early travel plans, for fear that prices may go up as well. In these cases, you might want to check seating charts and try to guess at how full the flights are. However, if you notice fares are abnormally high, I think you can generally assume they’ll go back down, since you won’t be the only one waiting for a fare decrease.
Generally speaking, from HK to Europe / North America, I see China Eastern and Air China as cheapest options, and they’ll load the cheap prices into their systems very early. For these carriers waiting probably won’t do you much good, I don’t think they have as sophisticated revenue management as the Western carriers. Cathay Pacific is similar, but they tend to have a lot of destination based fare sales when there’s lots of empty seats.
Link to report: