Last Friday I went up for a quick instrument practice flight with a safety pilot. Since I got my instrument rating I'd filed and flown IFR a couple times, but haven't flown simulated or actual instrument since my check ride. I didn't want to lose the skills I'd worked so hard to develop, so it was time to go up again. What I expected to have happen would be three instrument approaches at a new airport, Modesto. Starting off a little behind the plane and not quite on track or glide slope and ending up pretty good. What I got was unexpected in many ways.
The sky over the bay had high clouds and it was cold enough that I suspected there would be icing in any clouds we would encounter. There was a build up of lower clouds over the ridge we would have to cross to get to Modesto from Reid-Hillview. RHV's ATIS reported an AIRMET SIERRA for mountain obscuration and an AIRMET ZULU for icing. Winds/temps aloft forecast -6 C at 6000 ft. Skies in the central valley were reporting clear. I had filed an IFR flight plan. The clearance I knew we'd get would put us straight into the clouds and potential ice. I decided to depart VFR with flight following and fly south to avoid being vectored into the clouds. There appeared to be less clouds to the south. We flew south and crossed the ridge near Hollister. It was out of the way but gave us plenty of clearance below the clouds and above the ground.
Once across the ridge I put on the foggles and re-familiarized myself with flying by instruments. After a bit I contacted NorCal and asked for practice approaches to Modesto. We got cleared immediately to the IAF for the GPS approach I requested and I fell into the rhythm of flying instrument approaches. I stayed on top of where we were and had to remind ATC where we were before we go to the IAF. By the time I was on the final approach course for the GPS I had things well dialed in. The safety pilot was using ForeFlight to track our progress and finally said, "OK. Now you're just showing off. Zero degree track error!" Well, the GPS indicated one degree error but I was happy and quickly adjusted to keep the GPS on zero error too. We reached MDA and I looked up. Right on the center line! It was nice. We went back around for the ILS and I felt a bit behind on that one. Well within PTS standards, but not as good as the first approach. When I peaked at the runway the second time at the DH (right on center line again) I took a glance at the clouds over the ridge between us and home and decided to not do the 3rd approach.
We turned towards the bay area and looked at the clouds. I climbed up to 4500 feet but my co-pilot estimated we wouldn't be able to cruise at 4500 without entering clouds. It looked like he was right. The skies were still clear or very high clouds where we were but the cloud layer we headed towards was not high. There were also more clouds than there were when we originally crossed an hour before. However, we could see clearly between the cloud layer and the ridge line. I tuned in to NorCal to listen to what was going on in the valley and heard a plane report icing. That re-affirmed my commitment to not exercise my instrument rating in the clouds that day.
I turned the plane south again heading the long way home to the pass between Los Banos and Hollister. That was the lowest terrain I knew of to cross the ridge and I believed we would have good clearance between us, the clouds and the ground. As we flew my co-pilot kept looking at the ridge line. I flew past a couple very inviting valleys that looked like they would cut through the ridge with plenty of space below the clouds, but I wasn't sure they would and I didn't want to find out the hard way. As we approached Los Banos I got the altimeter reading there to make sure I had an accurate altitude readout. We turned to cross the ridge at the San Lois Reservoir and followed the general route of the highway, well above the terrain directly below us and slightly above the highest of the terrain near us with the clouds what looked like 1000 feet above us. We turned north once we had the Santa Clara Valley made and flew back to RHV at an altitude of 2500 feet under a broken cloud layer at approximately 3500 feet with the city lights shining like jewels below. The sun had just set.
It wasn't the nice instrument approaches that stuck in my mind that night or in the days after that, or the green hills or clouds or the sun shining between the clouds and the ridge or the jewel-like lights; it was the fact that I decided to fly below a cloud layer, across a ridge (yes at the lowest possible terrain I could find), with a much lower ceiling than I ever thought I would do. Being me, I went and analyzed the route I took and found, if the clouds really were at 3500 feet - I think they were higher because they were above the 3500 ft peak we flew near - with me at 2500 feet crossing the ridge, the highest terrain below me on my route was 1500 feet. Giving me 1000 ft clearance above and below me. I double checked the low point on the normal northern crossing route between the valley and the bay and its lowest point was about 1000 ft higher. My instincts were right not to head that direction.
OK, I'm sure some pilots would ask what's the big deal. My husband is one of them. And maybe there isn't one for them, but I don't want to have any less space than that between me, cloud and terrain if flying VFR. Especially if there is ice in the clouds. Other alternatives also come to mind. Stay in the central valley for instance. Climb high and get a clearance to drop through the clouds into the valley thus minimizing time in the clouds? Climb high and hope to find a hole in the clouds to descend through and then turn around if no hole was found? All options. All overkill for the situation at hand.
I'm still thinking about this one... what is a minimum I can establish for VFR flying to ensure I don't find myself flying between cloud and ridge some day and straight into trouble? I know I can legally fly 500 ft above ground and 500 ft below cloud in an unpopulated area but I definitely would not want to do that. I still haven't decided what that line will be. I think it will depend on my familiarity with the terrain. If I don't know the terrain as well as I know this area, I will need to have plenty of clearance between me and highest peak. If I do know the terrain the minimum may between me and the lowest pass. I just don't know. But I guess the good thing is, that little, no-big-deal, practice instrument flight gave me a lot to think about. That flight is something to add to my bag of experience before my bag of luck runs out.
Update: After getting some input from other pilots I realize the thing that bothered me the most about this situation wasn't flying through a pass with 1000' above and below me clear. It was doing that without knowing for sure that I had the 1000' above and below me. I did what seemed right at the time. Which is fine and it worked. I would do the same route in the same conditions again without hesitation now that I know the terrain altitude better, but as an engineer it is an uncomfortable place for me to be flying without knowing. My pilot friends pointed out some other sources of information I could have used to help with my "knowing" on the fly, WingX has some nice terrain information features and the plane I was in had terrain warnings built into the GPS. I had both and used neither during this flight. At this point I think the issue isn't safe minimums... the issue is knowledge. If I have the knowledge rather than the guess I know I'll make the right choice.