I recall going down rear stairs, onto the tarmac, and then up stairs into gate 79 at SFO (This was in August 2001 off a Shuttle By United flight). But to me that is a horrible idea because:
A) You need to carry all your bags down the jetway stairs
B) You need to walk across the tarmac at an airport (safety?)
C) You need to climb back up the stairs into the terminal

A double jetway is much more logical.