Saturday, November 1, 2008
Flight Planning In The Real World
Realistic flight-planning requires far more than simply measuring the distance, figuring the book speed and fuel burn and then launching
|Photo by Mike Shore|
As a new pilot in the age of $0.40-per-gallon avgas, I was primarily interested in going places rather than droning around the local sky in search of the perfect airport hamburger. That was a revelation, too. I learned that a destination advertised as being 346 nm distant might be as much as 10% farther away in practical terms, simply because it’s difficult or nearly impossible to fly so precisely as to prescribe an exact great-circle arc.
I also learned lessons about tailwinds. The tailwind that was promised as a 20-knot component on the outbound leg might rarely reach that speed, at least not until I was headed home in the opposite direction against what had become a headwind. I learned the hard way to be a cynic about every aspect of flight-planning, not because anyone was necessarily lying about the winds or the airplane, but because experience suggested that the reality almost never met the expectation.
Today, of course, operating handbooks are slightly less optimistic, the science of wind forecasts has advanced exponentially and the GPS has relegated the whole question of flight-planning to insignificance.
Or has it? While it’s probably true that few pilots navigate by pilotage or point-and-shoot anymore, flight-planning is still far from the slam dunk you might imagine it to be.
Weather is the first area in which you may find it necessary to ad lib more often than you think. It’s true that briefers are paid to be pessimists and to intersperse virtually all briefings with comments about “VFR not recommended,” but even when conditions are advertised as good, they may not be that far from bad.
Clear-air turbulence is one common manifestation of unstable weather that can demand special attention. If you’re flying VFR, the best advice during moderate to severe updrafts and downdrafts is to go with the flow (within reasonable limits) and allow the altitude to vary rather than fight the vertical currents to keep the airplane at the same level. Obviously, this won’t work on IFR flight plans or in actual IMC weather, but it can save time and work on most purely VFR flights.
I fly a modicum of hard IFR on international delivery flights (at times operating in all kinds of meteorological misery—icing, heavy glop and other fairly unpleasant conditions), and instrument weather nearly always slows things down five or 10 knots. Much of that’s a function of the wing being less efficient in rough air than in smooth air, but even in soft IFR, it seems any flight in the clouds nearly always requires more time than a VFR trip.
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