There are two main locations at the treshold of Runway 31. One is on the perimeter road from the Terminal to Hal Far, and the other is an elevated field beside the runway.
To get there, just follow the road from the Terminal towards Hal Far. Once past the runway treshold, turn on the second turn right and proceed along this narrow alley, turning right to get to the spotting location.
From the road, it is possible to get shots of planes on finals, but the angle will pretty much be a low-angle and liveries might not always be clearly visible.
The field alongside the runway is to be used from around 12:00 onwards.
From this location, you get a much better angle of planes "floating on the runway" seconds before touchdown.
However, in Summer, it is advisable to shoot the aircraft before they overfly the tarmac, as this reduces heat haze caused by the hot surface.
Lens-wise, you would be needing 100-400mm, depending on the size of the aircraft you are shooting.