Monday, August 4, 2008

How Far Can You Go?

I did a couple of trips last week as a "hired gun" first officer for a local company. These are fun, and the pay is pretty good. They only let me fly the empty legs, which seems fair, but the head of their flight department respects my experience and encourages me to do some instruction. I usually find something worth discussing, so am comfortable logging the time as "dual given." Some regulation junkie will probably find a way to say that this amounts to padding my logbook; he or she is entitled to that opinion. But when the pilot involved knows more at the end of the flight than at the beginning, I say that instruction has been received.

The big surprise this week was a flight plan to the midwest. I hesitate to call it a plan: there were only two fixes, the departure airport and the destination airport. This has been a topic for friendly debate between me and this company's pilots. They contend that this kind of planning tells Air Traffic Control (ATC) that it is OK to send the airplane wherever works best. But you know what? ATC will send the airplane wherever works best anyway. So there is no advantage.

What advantage do I see? Imagine a trip of 1000 nautical miles. This is almost 5% of the Earth's radius, so the big picture really comes into play.

  • If there is a center of high- or low-pressure, you can save a lot of time by passing on the proper side (when westbound, choose the polar side of a high, the equatorial side of a low). In this case, there were no major high- or low-pressure centers along the route. This route is long enough that terms like "polar" and "equatorial" really mean something.

  • You have no idea what the computerized flight planning software uses to estimate the winds aloft, because it all gets rolled up into one composite estimate. It is very unlikely that the winds will be unchanged over a route that long. Your strategy will be a lot different if you are flying into a decreasing headwind than if you were flying into an increasing headwind. This strategy depends on...

  • You don't have a howgozit. That's a corrupted spellingof "How goes it?," i.e., judging whether you are making adequate progress or not. [Gulp: a google search for "howgozit navigation" comes up with my book first!] Will you have enough fuel to make it? The last part of our flight would cross a significant amount of Great Lakes water, and the possibilities for refueling over the Great Lakes are few, so we would need to know early that there might be a fuel problem.

    The thing is that if it appears that you will be short of fuel, and you have a solid forecast of a decreasing headwing/increasing tailwind, then you are not short of fuel. If it appears that you are short of fuel, and the forecast is less than solid or the headwind is forecast to increase, then you are really short of fuel.

  • The comparison between the actual winds aloft and the forecast winds aloft is one of your best tools for judging the accuracy of the forecast. But this is impossible if all you have is one composite number that is supposed to work for 1,000 miles.

  • On the other hand, I really expect to fly direct. I compare the time abeam the fix to the predicted time to decide whether I am ahead or behind.



    We had a pleasant trip, except for dodging a few thunderstorms. We talked about some of these issues. On the way back the captain put a few waypoints onto his flight log.

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