Single pilot reported the loss of the GPS navigation system during landing approach. The pilot disengaged all related navigation systems and manually completed a safe landing for maintenance support.

Narrative

I was flying inbound to Stinson airport and had just been cleared to enter right downwind for Runway 14. The aircraft is equipped with a Garmin 430w; dual Garmin G5s for attitude and heading information; and a GFC500 autopilot. The Tower had instructed 'fly to midfield; then enter right downwind Runway 14'. The aircraft was configured for a descent; on autopilot; with Direct To SSF commanded on the Garmin 430w. The autopilot was in GPS/nav mode; following the 430w directions to SSF and vertical speed mode; in a 600 fpm descent to pattern altitude (1600 ft bugged; ALTS in standby). At approximately XA:36 AM central time the autopilot began to command a right turn. I immediately disconnected the autopilot using the yoke mounted autopilot disconnect button and hand flew the airplane. I looked down and noticed the bearing pointer on my HSI had turned. I ensured the airplane was still properly configured for descent; then checked the 430w IFR navigator. I hit DIRECT TO on the navigator and ensured SSF was the intended destination. The navigator had a pending MSG; which said 'Steep turn ahead'. I quickly took pictures of both the navigator and G5s; queried the tower to see if GPS anomalies were reported in the area; then set the problem aside and flew a normal visual approach and landing to the airport (this was VFR and I had the airport in sight; so the navigation was not necessary). Once safely on the ground at the airport I checked GPS position on the 430w moving map; and the aircraft position appeared correct as I taxied back to [the ramp] (at approximately XA:40-XA:45 AM). I believe at the time of the incident I was roughly 5 miles south west of Stinson airport. Studying the photos; I see no annunciation with regard to GPS integrity being compromised. The Garmin G5 displays 'GPS TERM' on the HSI; indicating terminal navigation mode which is appropriate to how the navigator was setup; and the magnetic heading information on the G5 matches the compass. The 430w is set to navigate Direct To Stinson; displays 'TERM'; and is not in OBS or VLOC mode (GPS is displayed above the bottom left CDI hotkey). The track indicated on the 430w matches the track of the aircraft; but the Direct Track to destination is incorrect - I could see the airport off my nose to the right; but the 430w seemed to indicate the airport was behind me and to my left. I have had GPS position loss before due to GPS Jamming; but that generally displayed a No GPS error or something similar. I have never had an incorrect position report for any aircraft; and have roughly 100 hours in 430w equipped aircraft and over 100 hours in GTN650 equipped aircraft; and have experienced multiple incidences of GPS jamming. I would have expected that any issue verifying GPS integrity would result in a failure message on the IFR navigator; and not an incorrect position report.