[Still Thinking]

It is, incidentally, one of the few dated moments in this 50-year-old novel, this “ray screen” business that kills “magnetic,” by which one hopes Rand means “reciprocating” engines.

That annoyed me too. I could see it killing her alternator (did they use alternators or generators in 1957?) and obviously her compass, and probably her radio, but her motor and flight controls, which probably would have been cables and linkages, should have been clicking along just fine.

[whodathunkit]

...that kills “magnetic,” by which one hopes Rand means “reciprocating” engines

I think the reference was to the magneto type ignition system which uses magnets to generate electricity and therefore spark. The magneto system is used in aircraft due to it's utter reliability, permanent magnets being very dependable.

Reference Wiki-"The magneto is now confined mainly to lawnmowers, chainsaws, and internal-combustion aviation engines."