Mechta,
that was also my understanding regarding low wings and ground effect. But the wiki page for the Bae146 suggests -
" The chosen configuration had a high wing and a T-tail to give good short-field performance, "
can anyone shed some light on this? I know that a t-tail config makes the stab and elevator more effective as it places it out the way of the downwash from the engines but I still fail to see how both benefit a short t/o