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from Pocket Learning, January 2006 In every kind of flying, whether helicopter or fixed wing, whether gyroplane or airship, whether glider or hot air balloon, knowing where the winds are is of critical importance. Good preflight action for all categories of aircraft includes determining winds aloft as well as surface conditions. For fixed wing aircraft suffering an engine failure, knowing the direction of the winds will keep you aloft for the longest possible time so that you can think it through. Seaplane pilots use this critical information to determine which direction to land on the water. Gliders use winds aloft information and lifted index information to hunt precious thermals which keep them aloft for the longest period of time. All landings for fixed wing aircraft should be into the wind with a clear understanding of wind direction to properly compensate for crosswind conditions. The biggest fixed wing sin imaginable is landing without looking at the windsock so you know exactly where the winds are. Read the associated article on Crosswind Technique. For instrument pilots of all categories of aircraft, knowing the winds aloft will assist you in setting up proper timing of holding legs. Knowing the surface winds is also a must because you'll need to adjust your indicated airspeed on the approach to have proper timing from the final approach point to the missed approach point. For rotorcraft (helicopter & gyroplane) aircraft, having an understanding of the direction of wind can assist the pilot in autorotative descents. For helicopters, knowing the direction and strength of the winds will assist the pilot in reducing the likelihood of loss of tail rotor effectiveness. The helicopter pilot's landing is typically into the wind as well with downwind landings typically never done. For gyroplanes, a proper landing requires knowledge of the wind direction in relation to the landing runway. For lighter-than-air aircraft, knowing the direction of the winds aloft will give you an understand of where you are likely to go while aloft. Airships (blimps) find it especially difficult overcoming strong winds aloft of 20 knots or greater. Surface winds of 7-10 knots (and greater) make landings a real challenge for the LTA crowd. For all categories of aircraft, knowing the winds aloft will give you an idea of weather to come. For example, winds aloft from the southwest indicate rain if you live on the west coast of Florida or California. A thorough cross country plan includes a phone call to pilots at your destination. The locals can teach you these predictable local weather patterns. Such a phone call will yield local intelligence such as tricky crosswinds across the ridge at St Steven New Brunswick airport, or the serious wind shear as a result of volcano steam at Kailua Kona in Hawaii, or the tricky westbound night departure at Cedar Key Florida with its short runway, featureless terrain. How about the "one way to land' airport at St Lucia which forces you to land towards the mountain and take off away from it regardless of the wind. Flying over bodies of water at night without reference to a horizon, unexpected wind shift below a ridge line or severe wind shear can surprise even the best pilots among us.  These examples should convince you of the importance of knowing wind information both at the surface as well as aloft. Its a critical skill that pilots take years to develop. Here are a few tips that will assist you in determining wind direction. 1. All the seaplane pilots know how to read lakes. They look for the glassy smooth band of water on the upwind side of the lake. Wind intensity will whip the water into foamy peaks which will streak in the wind direction as shown to the right. Light winds will provide a glassy surface with little movement other than natural wave action. Anchored boats will point into the wind. 2. Fire usually generates smoke which can give you a great idea of where the wind is coming from. Look for wild fires, chimneys, power plants, and industrial areas. 3. Reading signals from man made objects, including windsocks, flags, banners, and streamers. 4. Birds give us a great idea of where the winds are and what they are doing. Often you'll see birds circling in an updraft (thermal) which gives them altitude. You'll often see birds gliding (into the wind) without flapping their wings. While they are losing altitude, their nose into the wind reduces altitude loss and gives them a break from flapping.  5. The prevailing winds can be determined from the shape of trees, plants, dunes, and other natural features. Persistence forecast theory states: "what normally goes on is what's going on now." 6. In a hovering helicopter, the pattern of vegetation movement underneath will indicate the wind direction. The smallest amount of vegetation movement will be on the upwind side of the helicopter as depicted to the right. 7. Enroute, listen to ATIS/AWOS broadcasts to determine wind direction. Listen to unicom frequencies to hear what runways pilots are using. Have any tips to share? Send them to me... I'd like to hear your stories... How to read winds aloft reports Winds aloft reports are used to calculate
headwinds to
determine time to destination. Winds
reported in degrees true north, temperature in °Celsius. 
Above is translated as: Winds aloft report issued on the 14th day of the month at 1200 Zulu for use 0900 to 1500 Zulu. Temperatures are always negative above 24,000 feet (MSL). Codes reported as 9900 are light & variable. To convert wind directions reported greater than 360, subtract a 5 from the first number to determine wind direction and add 100 to the wind group. Example: 7508 = 250º at 108 knots. Winds greater than 200 knots are reported as 199 knots. Example: 7599 = 250º at 199 (> than 200kts).
Another Neat Report
Another neat report is the Lifted
Index Analysis – This report
indicates
the stability of air (Lifted Index) and the probability of Thunderstorm
Activity (K Index). A Lifted Index (top
number) from 0 to -2 indicates relatively stable atmosphere while -3 to
-5
indicates moderate lift, and ≤ -6 indicates strong lift.
The K Index (bottom number) indicates
probability of thunderstorms. Values of
< 15 indicate 0% chance, 15-19=up to 20%, 20-25=up to 40%, 26-30=up
to 60%,
31-35=up to 80%, and above 35 indicate 81% to 100% likelihood. |
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