The “SkyDeck” in terminal 2 of HKIA is the only “designated” viewing location at HKG, meaning that it’s probably where the airport authority would prefer that we spot from (especially considering you need to pay to get in). However, that doesn’t mean that you can or should only spot here, as the airport authority can’t and won’t stop you from spotting elsewhere. That being said, this is where I always go when the 25 runways are in use, as it’s perfect for 25R arrivals and very convenient. You don’t need to mess around switching between the Tung Chung line and various buses to get there, as SkyDeck is located in the main passenger terminal, meaning you can easily take the Airport Express or a taxi to and from. There are also restaurants, bathrooms, and even a movie theater, whereas most of the other locations are in the middle of absolutely nowhere.
The only real con of this location is that it’s only good for 25R arrivals. 25L arrivals and 07R departures will be heavily backlit most of the time, and 07L arrivals take place 3km away on the other side of the airport. Taxiway movement is quite far away, and often blocked by the terminal building. For 25R arrivals, you’ll need a focal length of 150mm on an APS-C camera for a 777 and almost 250mm for a narrow-body A320 or 737. Do the math and this equates to roughly 250mm to 400mm on a full frame.
To get here you’ll need to somehow get to the airport passenger terminal. Whether you take the Airport Express (highly recommended) or a taxi (less recommended), well that’s up to you. Once you arrive, follow the signs to Terminal 2 (the smaller building meant for LCC’s). Next, go all the way up to the highest floor where there’s a food court and several other restaurants. Then walk to the northern end of the terminal building, and you should see the Aviation Discovery Center and movie theater. The entrance to the SkyDeck is inside the museum, and you’ll need to purchase a ticket (15HKD) from the cashier. Then continue walking deeper inside the museum, and you should find the entrance to the SkyDeck, which you’ll need to take an elevator in order to access.
Link to the Aviation Discovery Center page on the airport webiste: http://www.hongkongairport.com/eng/shopping/entertainment/t2/aviat/avia.html