Tailskid
I believe mmrasi is on the correct path, the 900ER has a 2 positions tailskid, monitored by the SPSEU, electronic control, hydraulically actuated.
SPSEU light would light up if it does not work.
All of the info is from Cockpit companion, I haven't got acces to the official 900ER manuals, so can't check if it is in there.