Bandit
I guess the phrase "you can draw a horse to his water, but you can't make him drink it" comes to mind.
It must be a tad disappointing, but I wouldn't force the issue, you have the right idea by leaving it alone, I guess you could try and get him more actively involved, rather than pointing at the ones in the sky, take him to Heathrow and show him how big and powerful they are etc.
About taking him up, this is a difficult one and probably only you can judge, I asked my 2½yr old if she wanted to come to the airport with daddy to see the plane he flies, she jumped at the chance and was very excited, as soon as I wanted to sit her in the seat for a closer look she turned into a jibbering wreck.
I'd say just keep going as you are, if he likes them great, if not, so be it
