It is relatively easy to "fly under radar."
***
Just to "cover bases"...
Any civilization capable of reaching earth from a distant planet would be able to pluck a plane from the sky.
Such extraterrestrial intervention is a vanishingly remote possibility but not inconceivable.
For the time being, the prospect adds to the Magnum Mysterium.
For the time being, the prospect adds to the Magnum Mysterium.