Pontius, magnetic detectors are "another square law" device. The closer you are the smaller an object you can detect. And since you're expanding much like a radio wave as your "surface" gets twice as far from the detector the signal is reduce by twice squared or four times.
And with this plane I get the impression there are some largish metallic items to find such as the engines. The rest is basically non-metallic or small. But, of course, aluminum is not particularly a live item for magnetic detection.
All that can really be said is, "It's been done before. If it is important enough this time it'll likely be done again."
{^_-}