Last theory from the Smolens.ru forum.
The outer NDB with marker in Poland is usually 4 km from the threshold,
and the inner NDB with marker - 1 km.
It has been confirmed, that the outer NDB in Smoleńsk,
due to terrain situation was 6 km from the threshold.
(Which is quite common in Russia.)
If you assume the 2,6 deg glide-path the 2 km error in distance
would result in 90 m altitude difference at the 1 km NDB,
which corresponds approximately to the altitude deficiency the
accident aircraft experienced at this point.
The pilots, assuming outer NDB at 4 km and following the
normal glide path were 100m lower then they should be.
Continuing with the angle of 2,6 deg they were still 2 km
from the runway, at the moment, when they expected threshold,
and at 1 km from the runway already below the runway level...
Fits the fact known until now quite well.
The lowest line in this diagram corresponds to 2.66 deg from 6 km NDB.
It's 0m QFE point is exactly 2km back from the touchdown point 300m
down the runway.
Plausible?
Anyone?