I'll take a crack at this one; here's how I understand the "flying" piece.
It's has to do with how those forearm angles/wedges relate to one another and the selected plane. The right and left wedges should be perpendicular to one another...it keeps the left wrist flat through impact and controls the clubface. The wedges also have specific alignments to the selected plane during the swing (different for swinger and hitter); regardless, the wedges "fly" as a single unit, aligned on plane, into and through impact.