I don't go with the gravity waves theory. Instead, I heard that it's something to do with dark matter, which is attracted to and congregates around all objects that have mass, like trees, the ground, people, fence posts and similar things. When your plane arrives in the vicinity of this dark matter, a different force field engulfs it and sucks it in. This force field is part of the explanation for why gravity is much lower than it should be. it's the greater part of the field that would be gravity that occupies different dimensions from the ones we exist in, so it can't be measured, neither can its effect be proven with our maths, but nevertheless it's definitely there and active. You will see it for yourself whenever your plane is in the vicinity of those objects.
I got this from the aliens when they abducted me and took samples of my DNA, they asked me if they could do anything in return for it, so I asked them to explain this phenomenon, mainly in relation to why people who are either walking straight or standing still, always suddenly step into my path when I ride my bike near them, but I also noted that the affect on model planes must be from a similar cause. This was how I understood their explanation, but I must admit that some of it went over my head. Next time I see them, I'll ask if they can explain it in simpler terms.