Friday, March 6, 2009

Line of Sight

Winds aloft were 260 at about 35, and the plan for my instrument student was to fly a little triangle (JATTS - ROCCA- PIH - JATTS) based on two local VORs. The strong wind mean noticeable wind correction angles on the north-south legs, and ridiculous groundspeeds on the east-west legs. The first lap would be with me flying the heading he commanded, and, of course, no hood. The next lap he would do it all, under the hood.

But we were in his airplane, not a rental, and the wind was gusting to 32 knots. Was he up for it? Absolutely!

We fooled around with E6Bs to estimate the wind correction angles and crosswinds on each leg. These worked out to be 12 degrees on the north-south legs (his first guess had been 30). He picked a heading to intercept the northbound airway, and we launched.

The ATIS said that the cloud bases were at 3600'AGL, but in fact the ceiling was around 2000'. We weren't equipped for ice, and there were no pilot reports about icing or tops, so we cruised along at 1500' AGL (500' below the bases), getting bumped a little but having fun.

The #1 VOR was set to PIH, with the OBS on 318. The #2 VOR was set to IDA, with the OBS set to 233. At first we focused on #1, but he began to wonder when the needle on #2 would start to move. "Be patient," I counseled, but I know that's hard. I made him ignore the handheld GPS on the windshield post and estimate how far along the airway we were.

But the impatience was too much. "We've still got a NAV flag on #2," he said, which is a pretty sharp observation. There was no audio identifier, either.

"How far are we from the VOR?" I asked him.

"Can I use the GPS?" he asked.

"Sure, I replied, but it's about 42 miles."

He punched some buttons. "Forty-two! How did you know that?"

So I showed him on the chart how JATTS was 40 miles from IDA, so the distance was a little more than 40 miles. The extra 2 was a lucky guess.

"So why aren't we getting IDA?"

The answer, of course, is that we were too low. VHF and UHF signals are line-of-sight, and we were below the horizon.

This incident reminded me that practice is an essential part of learning. We hear and read that VOR signals are line-of-sight, but the visceral knowledge (what Heinlein called "grokking") does not begin until we experience it in the field. Doctors don't just go to medical school: They spend more time in internships and residencies, practicing with whatever patients walk in the door. Cooks don't just read recipes; they cook, based on what is ordered, and learn to adjust for the variations inherent in ingredients, weather, tools, and the like. I've heard the great chef Escoffier quoted as saying "A cook does not know how to prepare a dish until he has prepared it 1,000 times."

But some people seem to think that you can train a pilot in a simulator. A simulator is a wonderful tool; see this post about how I'm using the X-Plane app for the iPhone to improve my own glass cockpit scan. But it has limitations. No simulator session involves flying at a low but safe altitude over the desert and trying to navigate by a VOR that is too far away, or whose signal is blocked by higher terrain in between. Simulator training alone does not make a pilot (see Windsor's comment on this post).

Pilots need to practice, just like doctors.

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At March 9, 2009 at 8:51 AM , Anonymous Sarah said...

Of course it was. "42" is the answer to most questions, and a good guess.


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