To represent fading, i follow gregg cooper's article and the amazing finish he had on his J1n1 Gekko. You can find it
http://www.features02.kitparade.com/gekkogc_3.htm
. As for a dirty plane, i guess u could use ground up pastel chalks, a wash, or like i do, using a artist pencil, i draw in the panel lines, then with an artist's blending stump, smear the graphite outwards.