First time i had my desktop with my on the plane I just took out the GPU, put it in a anti static bag then I wrapped that in bubble wrap and duck-taped it inside my case and then put the case inside a suitcase filled with clothes.
The second time I brought it with me on the plane i had switched from a AIO water-cooler to a tower-cooler. So i took out the cpu cooler and graphics card, Bubble wraped that stuff.
Both times it was successfully sent as luggage