Suppose there is a tetrahedron $SABC$ with $S$ being its apex, and $H$ being the orthocenter of triangle $ABC$. When is the line $SH$ perpendicular to the plane $ABC$ except for the case of $SABC$ being a right tetrahedron?
I'd like to know if there are any other cases and how do you find these. Internet gave me no visible information of that.
Thanks in advance.