Aviation Daily 9 Nov 1971 says San Diego runway 27 was getting a two-step VASI: a two-bar flashing VASI "in the approach clear zone" set at 5 degrees and standard three-bar "alongside the approach end of the runway, set to provide a 3.25 degree glidepath beam from an altitude of 200 feet above the runway surface."
"A normal transition to approach will place an aircraft on a glidepath below that indicated by the flashing two-bar VASI and above that of the three-bar installation. Consequently, the lights of the former appear red and those of the latter white. As the appropriate glidepath is intercepted for five-degree descent, the upper row of flashing lights appears red and the lower row is white. As the shallower glidepath of the standard VASI is intercepted, the upper row of lights on that installation turns red. When the middle row lights also turn red and the lower row remains white, the aircraft is on the proper descent path."
How long did that last?