Photographing airliners can be a little “samey” since there are lots of very similar jets and getting a shot of them from the side looks much like any other shot unless the aircraft is specially painted or the lighting is particularly unusual. Consequently, every once in a while, it is fun to try and shoot from a different angle. The approach to SEA when the planes are on a southerly flow brings them in over a part of Burien where you can get yourself pretty much under the flightpath.
It won’t take too long before you are again getting a sequence of repetitive images, so it isn’t going to be useful for much time, but it is a chance to do something a little different. Head on shots from a distance are possible. Then you can get the shot looking up from the underside. This might be a tight shot of a part of the airframe, or a wide angle shot of the whole thing. An opportunity to do something a little different when you are photographing aircraft that are not ones where you care about missing the shot as you might when something special is coming in.