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Its placement would have to be quite close to the tail, based on the scarcity of additional debris found near the tailplane wreckage, and a pretty powerful one at that, given that the tail is generally considered as the most structurally robust part of the aircraft, n'est-ce pas?"
It takes a surprisingly small amount of explosive to remove the tail from a pressurized airliner at altitude.
Less than the size of 2 cigarette packs.
Placement isn't all that critical, either.
Tests were done after Lockerbie, you can see the results on Youtube