Putting on salesman's hat:
No. No. No. No... you should get a new lens. Get the Canon 70-200mm f2.8L II, while you are at that, you should also get the 300mm f2.8L and if can, get the new 200-400mm lens. With that combination, you can take sharp pic of aircraft far far away.
Putting on economist hat:
You really should spend more money, that will keep our economy going and save thousands of jobs, from the operators to the designers to the salesman and the sweeper, packers, etc etc.
Putting on friend hat:
After you buy the 70-200mm f2.8L II, can lent me for a couple of days? Pretty please?
Putting on adviser hat:
Yes, you probably shouldn't buy anything now. Go out and rent a 70-200mm f2.8L lens, see, play for awhile and see if it can achieve what you like. if cannot, then stay with your 18-200mm, if it can... then ditch your 18-200mm and get the 70-200mm f2.8L. Please also note the weight of a 70-200mm f2.8L is significantly more as compared to the relatively light weight 18-200mm.
Okay LexenZ, choose from the above advises - salesman, economist, friend and adviser... see which one suits you better.