Capn Bloggs:
"On ILS approaches, stepdown fixes are established for obstacle or traffic separation.".
"On both days your flight path on the glide slope was the same, but on the hotter day, the stepdown altitude, crept up into your glide path."
How is a hotter or colder day going to change the vertical separation with terrain when tracking the glidelsope?
Fair enough steps limited by airspace (1900ft at the bridge!) are affected by temperature and pressure when on the GS but obstacles?
The GS isn't affected by temperature but step-down fixes are. The GS cannot be used as primary for vertical navigation until the P-FAF. The step-downs are primary for vertical guidance prior to the P-FAF. Step-down fixes rise when its hot and descend when its cold. The hot day is when separation from other aircraft can be lost.
On a really cold day obstacle clearance can be lost.