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
|Any wind from a consistent direction will usually be a losing proposition on a round-trip flight because a headwind, such as the 52-knot winds encountered on a leg to Palmdale, Calif., acts on the airplane longer than a tailwind. |
Altitude selection is another area where you need to have an open mind. Many pilots planning a long flight tend to concentrate on picking a single altitude for the entire trip, even if they’ll be transiting 700 to 800 nm of terrain. That’s far enough that you may be transiting several weather systems, and the change in flow may dictate variable altitudes for such a flight. You may want to consider starting at 8,000 feet at the beginning of a trip, climbing to 12,000 feet halfway through the hop, then descending to 6,000 feet for the last hour.
It’s true that most pilots are smarter than me and don’t fly across oceans, but if you operate over long distances on a regular basis, you may be well served to have a liberal attitude about altitude. In turbocharged or pressurized airplanes, for example, I’ve sometimes varied my height above sea level by 16,000 feet or more on the 2,160 nm leg from Santa Barbara to Honolulu, starting at 6,000 feet in the prevailing headwinds near the California coast, and gradually ascending to 22,000 feet or higher as I come under the influence of trade winds 1,300 to 1,500 miles out.
|Plugging in a direct-to destination on a GPS unit will give you the great-circle distance from Point A to Point B, but direct flight may not be possible due to airspace restrictions. |
If you fly above the plains of the Midwest or along the flat beaches of the East Coast, you may be able to travel the direct route pretty much as offered. If there are mountains or bodies of water in the way, however, you may find the GPS distance to be impractical.
Similarly, the advent of data linking in cockpit weather devices has made pressure-pattern flying, e.g., following the optimum winds, more reasonable. If you’re operating in the vicinity of a low-pressure system with counterclockwise flow, you might want to fly to the right of center, with the wind at your back. A high-pressure system suggests flight to the left.
In my Mooney, my little backup Garmin 496 with weather uplink plots those wind patterns for me and allows me to interrogate the winds aloft for the most efficient routes. That’s not necessarily the shortest route, but it may be the quickest, and that’s usually all that matters. Successful pressure-pattern operation is usually contingent on either very tight systems or long-distance travel to make the off-course variations worthwhile.
Speaking of winds aloft, it’s important to remember that any wind from any consistent direction will usually hurt you on an out-and-back mission. (In 42 years of flying, I’ve had tailwinds in both directions exactly twice.) Direct headwinds and tailwinds are the easiest to manage, as they don’t balance each other on a round-trip. Even if a forecast tailwind on an out-and-back mission does materialize, you’ll usually lose speed with wind from any direction on a two-way trip. That’s because a headwind acts on the airplane for longer than a tailwind. To use a simple example, a 100 nm trip in a 100-knot airplane with a 20-knot tailwind requires 50 minutes outbound and 1+15 return for a total of 2+05 (versus 2+00 for the same trip in no-wind conditions).
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