This happened to me about a year ago on that approach (I'm based at
SQL) and sounds like almost the same point. It all came back after
about 15 seconds, the RAIM flag went away. I don't recall whether I
was still in approach mode or not, but like you I broke out about the
time I was figuring out my next move.

I've wondered whether there's some kind of signal interference from
the Stanford/SLAC vicinity once in a while. (This is pure speculation,
I have no data to support that.) Something also messes up 119.0 (tower
freq) in that area all the time.

-Jon C.


"G. Sylvester" wrote in message
...
I went up for currency with my (former) CFII. We were flying back to
San Carlos (KSQL) and on the GPS 30 approach. We were cleared to
depart OSI at a heading of 140. Norcal informed that they are going
to fly us 7 miles past AMEBY. They flew us about 3 miles east south
east of AMEBY when they had us do a left turn direct AMEBY. I was
perfectly established and 2 miles out from the FAF the Garmin 430
went into approach mode. I had the needles perfectly centered about
1 mile from CUZUP (FAF) when I was kicked out of approach mode. We
stayed at that altitude as we are very familiar with the approach and
terrain and we skimmed one very thin cloud for about 5 seconds and
then went fully visual. During that time my CFII did a RAIM check.
I thought it passed but maybe I'm wrong. On the ground, he was
unsure why we were kicked out of approach mode. He thought it might
be because we were more than 25 (?) degrees off of the AMEBY-CUZUP
course but then again it definitely went into approach mode before
that. We were kicked out while theh needles were dead centered.

Any ideas?

Gerald