M-20 K (231) / Encore
Flight Crew Instrument
Flight Crew Last 90 Days 6; Flight Crew Total 1500; Flight Crew Type 500
Training / Qualification
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Unstabilized Approach
Flight Crew Executed Go Around / Missed Approach
Airport; Human Factors; Aircraft
First approach attempt was to Mandan (Y19). Reported weather was 300 ft ceiling with 2.5 Miles Visibility. I was established on the approach (RNAV 31) and shortly after the FAF; the approach downgraded to LNAV. The weather was below minimums for the LNAV; so I declared a missed approach and requested the RNAV 31 into BIS. After the IAF; approximately at the FAF; the approach downgraded to an LNAV approach. I was high on final and declared missed approach. By this time; I was lower on fuel than I expected and advised ATC of the situation. ATC advised they would provide ILS 13 to save time. The receiver did not provide accurate glide slope; but ATC advised altitudes at the fixes and landing was made without incident.After landing; two other pilots indicated they had experienced similar problems with RNAV approaches degrading at the same airports at approximately the same time frame. One pilot also reported he had been advised of difficulties with the localizer; but it may have been an incorrect configuration in the G530W on my part. I intend to practice more ILS approaches and also LNAV approaches. Overconfidence due to a [previous] near flawless approach may have led to being unprepared to fly the LNAV GPS approach to low minimums.
Mooney K pilot reported difficulty with RNAV approaches degrading to LNAV on approaches to Y19 and BIS.