What's confusing me is why engine power would be lost. All else aside, jet turbines don't require electricity to keep them going. Maybe to get them started, but that's all.
Dumb concept and poor execution. It's the only valid answer. Mechanical systems still work (flintlocks, crossbows, modern firearms, etc.). Chemical systems still work (stills, gunpowder, etc.). Fire still works. Hell, even electricity
still works, else everyone would be dead and the magical talismans wouldn't be able to power up on their own (and those must be some crazy awesome batteries they have to be able to produce such a powerful effect even 15 years down the line).
The only real explanation is that a wizard did it. And that's about as stupid as it gets.