Training Tip: Not-so-easy breezy
The winds aloft at 30,000 feet over Massachusetts’s Nantucket Island were from 240 degrees at 98 knots, and the temperature was minus 47 degrees Celsius as the third in a series of recent snowstorms advanced on New England, according to the National Weather Service’s Aviation Weather Center website.
If you were jotting down that information during a phone weather briefing, you could transcribe it as a concise “249847,” as it appears in published winds and temperatures aloft forecasts. But had those winds been just two knots higher, with direction and temperature unchanged, the published data group would look like this: 740047, which doesn’t resemble a wind speed and direction data group.
OK, we get it that you don’t fly your trainer at Flight Level 300. Even if the aircraft could reach FL300,100 knots is probably above the wind limit your flight instructor has authorized. But play along for the next few paragraphs, perhaps to ace a knowledge or oral exam.
First tip: There’s no direction—true or magnetic—represented by the “74” in 740047. But if you subtract 50 from 74, you come up with a normal-looking “24,” as in 240 degrees, which confirms what we know the direction in our example to be.
Next, handle wind speed the opposite way, using a correction factor of 100 to make the numbers sing in tune: It’s unlikely that the wind is 00 at 30,000 feet (well, maybe in the eye of a hurricane). Add 100 and you get a reasonable result that also clicks with the conditions given above.
The temperature is self-explanatory—except that the “47” in the data group 740047 means minus 47, as winds-aloft forecasts typically remind users with the note, “Temps negative abv 24000.”
If you find this business of code-and-decode frustrating, so did we when practicing explaining it to ourselves before attempting to explain it for you.
Sure, it’s mostly academic for now. But the question could appear on a test. Just remember to normalize the two-digit wind direction, which must result in 36 (for 360 degrees) or less, by subtracting 50 from what’s published.
Then add 100 to the wind value. The resulting forecast should make sense.
Do you have a handy method for remembering tricky ground-school material? Our friends at AOPAHangar.com would like to know about it.
