Commercial Fixed Wing
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 140; Flight Crew Type 10000
Human-Machine Interface
Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude
Flight Crew Overrode Automation; Flight Crew Executed Go Around / Missed Approach
Aircraft; Environment - Non Weather Related
We were cleared the RNAV (RNP) Y 16 L inside of HLDMM (I believe) on the KENNO 2 RNAV. 0.3 was entered into the LEGS Page and 4;500 feet was placed in the MCP (Mode Control Panel) window. Inside of KLOCK; zeros were entered into the MCP. At approximately 1;500 feet AGL; with the aircraft fully configured and a zero vertical NAV deviation; the Vertical NAV suddenly indicated approach 488 feet below the vertical path. The aircraft made a minor attempt with pitch and power to correct the deviation. I then disengaged the autopilot and autothrottles. By the time we sorted this out; we were too high above the glidepath for a normal approach; so I directed / executed a go-around.We subsequently flew a visual approach backed up by (a different RNAV) the RNAV GPS X Runway 16L. We did not engaged the VNAV / LNAV. An ILS is not available to 16L. The weather packet cover page did note GPS interference testing in the PMSR (Pt. Mugu Sea Range) centered on the SXC248/058 and possible impact areas; but RNO was not in the listed area.  RAF coverage was 0.3 or better. There was an FDC NOTAM for this approach (to disregard a note for night operations); but was N/A.  Company was contacted.
Air carrier Captain reported that VNAV suddenly indicated below glide path during approach to RNO airport. The approach became unstable; and the flight crew executed a go-around. Reporter stated that there was GPS testing in nearby area but the approach airport was not listed on the coverage area document.