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AOPA ePilot Custom ContentAOPA ePilot Custom Content

The following stories from the February 15, 2008, edition of AOPA ePilot were provided to AOPA members who expressed an interest in the particular subject areas. Any AOPA member can receive information tailored to their areas of interest by updating their preferences online.

My ePilot - Student Interest, Training Tips
One of the first weather products a pilot seeks out before flying is a surface analysis chart, and one of the most eye-catching features of that chart is the pattern of isobars arranged around high- and low-pressure systems. Isobars, defined as lines of equal atmospheric pressure, are as informative as they are visually striking. Isobars provide a ready look at how strong the winds are and from what general direction they flow. That's because winds flow roughly parallel to isobars-clockwise around high-pressure systems and counterclockwise around lows in the Northern Hemisphere.

"Isobars show pressure, and therefore, wind patterns. If a low is encircled by a tightly spaced series of isobars, then you know that the low is deep-one with strong, converging surface winds and therefore a lot of lifting power. If the low-level winds are converging, there's nowhere for air to go but up! So, chances are that during the ascent, there's condensation and cooling of water vapor. This situation often means you can count on low clouds and precipitation in the vicinity," Thomas A. Horne wrote in "Wx Watch: Isobars and Height Contours" in the October 2007 AOPA Pilot.

Why don't winds precisely parallel isobars? Several forces struggle for dominance, as Horne explains: "Wind behaves according to three main forces-pressure gradient, Coriolis, and friction. Pressure gradient force drives air toward low pressure centers, while Coriolis force acts opposite to this force. When pressure gradient and Coriolis forces are in balance, that's when air moves parallel to isobars. But friction can upset the balance by slowing wind speeds and reducing Coriolis force." That friction is introduced at the surface by terrain. Rougher terrain means more friction. (Also see Section 2 of AOPA's Handbook for Pilots.)

The link between isobars and winds is just one example of weather information available to any pilot with Internet access who does some homework before contacting flight service for a preflight weather briefing. To learn what else is available, and how to use it, read meteorologist Jack Williams' "Weather on the Web" at AOPA Flight Training Online. Study that wealth of weather on nonflying days too, for fun and to increase your piloting knowledge and skill.

My ePilot - Training Product
Looking for a new or replacement flight bag? Sporty's has revamped its Flight Gear line of flight bags and rolled out a selection with a host of new features. Among them: padded pockets for GPS units, cell phones, sunglasses, and other small items; padded headset pockets; padded straps to help you shoulder the load; and rubber cleats on the bottom of each bag to keep it elevated and clean. The complete selection can be viewed online. Prices start at $59.95 for the cross-country backpack. To order, see the Web site or call 800/SPORTYS.

Note: Products listed have not been evaluated by ePilot editors unless otherwise noted. AOPA assumes no responsibility for products or services listed or for claims or actions by manufacturers or vendors.

My ePilot - Student Interest, Final Exam
Question: If I'm in contact with air traffic control and getting flight following, does that automatically give me clearance into any type of airspace?

Answer: Using flight-following services does not absolve you of obtaining a clearance or communication requirements in certain airspace areas like Class B or C. More than likely the controller will have already coordinated your sequencing with other controllers pertaining to the direction you are heading, but do not assume and inadvertently enter the airspace if you get a gut feeling you might operate contrary to the FAA's Part 91 rulebook. It's better to query the controller to find out if you're cleared to enter. If not, request a temporary frequency change to make the appropriate contact yourself. Keep in mind that flight-following services are conducted on a workload-permitting basis and do not relieve you of your responsibilities as pilot in command. More on this subject is discussed in the Flight Training magazine article, "Flight Following: How to improve your flying enjoyment and safety."

Got a question for our technical services staff? E-mail to [email protected] or call the Pilot Information Center, 800/872-2672. Don't forget the online archive of "Final Exam" questions and answers, searchable by keyword or topic.

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