Backlit photography is when you take photos with the sun in front of you to try and create a silhouette effect or show different highlights of the aircraft.
Typically "best" practice photography is done with the sun behind you and nine out of ten times I tend to agree.
However some of the absolute best photos I have ever seen have been silhouetted backlit shots.
If you are trying to silhouette the aircraft turn the exposure down to -2 so it blackens the aircraft out and gives that definite assertion as to the type of photo you are trying to achieve.
Sunset and sunrise are generally speaking the best times to try for the silhouette effect when sun is just off the horizon and planes are in relativity close proximity to the ground.
Another exciting mix is when there is rain and the sun shines through the water illuminating the water droplets.
Mix it up once in a while, have go at shooting backlit in different weather conditions, adjust the exposure settings and ISO on your camera.
This photo below demonstrates beautifully the positive outcomes of shooting backlit.