Aileron

Today we made a right Dumbarton departure, meaning we flew runway 31 out and turned right at the Dumbarton Bridge to head east across the bay. Over the east hills, we practiced slow flight and stalls. Stalls are when the wings ask for too much lift, the air stops flowing smoothly over the wings, and the plane drops. They feel pretty benign in the 172 and it's good knowing I have to pitch the plane up a lot to get a stall to happen, since I'd rather not one catch me by surprise.

At some point, my CFI noticed a little flashing light and that the ammeter was reading negative. For some reason the battery wasn't charging. It was discharging. Our alternator had failed mid-flight and soon we would drain the battery, losing electrical power completely.

On the 172, the lights, avionics, and flaps are electrical. Thankfully it was daytime, and thankfully all the flight controls are connected with physical cables instead of fly-by-wire. If we lost the radios, it would be annoying landing in controlled airspace, but there are standard procedures for that and we had plenty of fuel to circle around or divert if we had to. We were likely to lose the flaps first, since they require the most power, but it's perfectly possible to land without flaps and, again, there are procedures for that.

We immediately set a course to return to KPAO and let tower know that we'd lost our alternator and that we might not be able to transmit soon. Tower asked if we wanted to declare an emergency, but my instructor declined. There was no imminent danger, just an annoyance. It felt good to at least get that message out, so that when we did lose the radios, tower would know why we were coming in without talking. We shut down the GPS units to conserve power but otherwise flew a normal pattern. On final we tried the flaps and they were still happy to extend, so we made a normal, uneventful landing.

• Flight Hours: Δ0.8   Σ14.2