What I Learned Today

Yesterday I had a lesson on high-altitude flying. We went up to Big Bear airport (L35) in the mountains above Los Angeles. Big Bear is at 6700′, and that plus some intervening ridges meant we chose a cruise altitude of 9500′. It takes a long time to climb from 300′ to 9500′ on a warm day! Big Bear is 60 nm from El Monte, and it took us over halfway to get up to 9500′.

The goal of this lesson was to learn not only about flying at high altitudes, but how to take off and land at high altitudes. The challenges arise from the fact that the engine’s performance is greatly reduced and the thinner air means the wings develop less lift. Here’s a terrifying tale of how not to do it. Big Bear is also nestled in the mountains, so there are some additional factors to consider in terms of likely updrafts and downdrafts and being mindful to always have one or more exit strategies in mind. Don’t get boxed into a canyon!

The winds were a little odd when we arrived – crosswind and gusty, and mildly favoring runway 8, which points into a forested area, as opposed to runway 26, which points into a lake (which therefore poses fewer obstacles). See image at right for what it looks like approaching runway 8 (image credit Mead & Hunt).

We tested it out by starting with a low approach over the runway – 300′ up, 70 kts, 10 degrees of flaps. We did NOT go full rich as I would normally do. That was my first deliberate low approach, and I’d been curious about how to do it. This meant I got to see how the winds actually felt near landing, without fully committing; midway down the runway, we went full power and did a go-around. Indeed, I could feel the crosswind and some airspeed oscillations from the gusts. And the climb out was weak, even at full throttle. And there were definitely up- and down-drafts and bobbling turbulence in various places. Still, nothing we couldn’t handle.

We came back around for an actual landing, which was beautifully smooth. I had pre-calculated the likely landing distance given the temperature and altitude, which was about 700′ (versus 570′ at EMT – not much difference) and indeed, it felt like a pretty normal landing.

We taxied back for takeoff and there I got to learn how to lean the mixture to get max performance – stand on the brakes, full throttle (only getting 2200 rpm when full rich!), then lean the mixture out (increased to 2400 rpm) but not too lean (we aimed for an EGT of 1300 F). Then – takeoff! I’d also calculated the takeoff distance (1440′ compared to 825′ at EMT) and this time I did notice that it took longer than I’d expect to reach rotation speed. But Big Bear has a 5800′ runway, and that’s tons more than a Cessna 172 needs to take off, even in those conditions (density altitude was about 8500′).

We also practiced an aborted takeoff – a surprise event that my instructor called just as I was about to lift off. Pull throttle to idle, keep the nose up, maintain directional control. Again, plenty of runway for us to slow and stop. This is a great option if the plane just isn’t developing enough speed or anything feels or sounds wrong.

In general, flying at Big Bear was challenging but doable. I felt that it was within my ability to keep the plane under control and doing what I wanted it to – but it took a lot more attention than usual, between the reduced performance, turbulence that induced sudden banks, altitude changes, and airspeed changes, and the gusty (and strongly variable) crosswind that kept playing with me as I’d approach to land. My instructor commented that in those conditions, it’s more about keeping the plane within a box of desired performance, since you can’t micromanage it to stay nailed on airspeed, altitude, descent rate, etc. with the constantly changing conditions.

Now I’m ready to fly to the Grand Canyon! (Almost the same altitude as Big Bear!)