20-Year Prospect
Yes, this job will still exist in twenty years, because—duh—so will airplanes.
But the growth prospects for this particular career field are terrible. See, older airplanes are being replaced by newer, niftier models, made with more durable materials that are less prone to going kaput. Fewer maintenance issues with a plane mean fewer maintenance personnel will be needed to maintain the airliner.
Take carbon fiber, for example, which was used in the building of the Boeing Dreamliner. (Yes, the Dreamliner is buggy as all get out, but it's still an incredible plane.) Researchers foresee a day when manufacturers will be able to toss out the millions of individual pieces that make up the modern jumbo jet, rebuild said pieces out of carbon fiber, and come up with fewer parts that are less prone to breakage.
Our advice, then, is this: You may love the planes of yesteryear, but if you want to be puttering around a hangar two decades from now, you need to get hip to the airliners of tomorrow.