Speaking Collins now, VGP is an approach mode for Baro VNAV that replaces VPTH. So, you enter an approach with a charted Baro VNAV descent gradient; arm APPR and VNAV, and intercept the course and path; the FD mode changes to VGP and the FD/ AP now behave like it is an ILS. Particularly the ALT Selector which can now be set to the missed approach altitude. The FD will NOT have a level-off altitude as in a non-precision approach with a MDA, the pilot will see a GP to the runway.
It does make compatible approaches more like an ILS; is not a substitute for LPV (it was developed prior to LPV) and is on all ProLine 4 and 21 installations, at least all Bombardier ones.
GF