In article ers.com,
David Megginson wrote:

The spar is typically below the floor -- I don't have a hump on the floor
of
my Cherokee,

What is that thing under the rear seat in my 140?

and I don't remember ever seeing one in an airliner. The
cargo
handlers will might to worry about it in the airliner, of course.

airliners have fuselages high enough that the passengers can be
above the spar.

--
Bob Noel