The Winds Aloft Forecast, the FB Encoding That Trips Up Every Student on Their First Cross-Country, and the Altitude Selection Tool Hiding in the Numbers

The Winds and Temperatures Aloft Forecast - commonly called FB winds after its original teletype identifier - is one of the most practical tools in cross-country preflight planning. It covers altitude levels from 3,000 feet up to 39,000 feet MSL and is issued four times daily by the Aviation Weather Center. Once you understand the encoding, it drives altitude selection, groundspeed calculation, and freezing level awareness.

What Does the Winds Aloft Forecast Actually Look Like?

The product is organized as a grid: station identifiers down one side, altitude levels across the top. Each cell contains a four or six-character code for that station at that altitude. For private pilot training, focus on the lower levels - 3,000, 6,000, 9,000, and 12,000 feet.

Each code breaks down the same way every time. Take 1825−08 at the 6,000-foot level:

• First two digits - wind direction in tens of degrees: 18 = 180° (wind out of the south)
• Next two digits - wind speed in knots: 25 = 25 knots
• Last three characters - temperature in degrees Celsius: −08 = −8°C

That single entry tells you: southerly wind at 25 knots, temperature minus 8°C at 6,000 feet.

How Do You Decode High Wind Speeds in the FB Format?

This is the encoding detail that trips up nearly every student on a first cross-country. The FB format was designed for teletype transmissions with character limits, so high wind speeds use a compression convention.

When wind speed reaches 100 knots or more, the encoder adds 50 to the direction digits and subtracts 100 from the speed. To read it, reverse the process: subtract 50 from the direction digits, add 100 to the speed digits.

Take 5735 at a high altitude level:

• Direction: 57 − 50 = 07, so 070° (east)
• Speed: 35 + 100 = 135 knots

That is a jet-stream-level wind. The tell is the direction value: if the first two digits fall in the 50s, 60s, or 70s, pause - you are looking at a high-speed encoding, not a wind actually blowing from the northeast.

This exact scenario appears on the private pilot written exam. A question like “what does 7730 mean at a high altitude level?” requires this step: 77 − 50 = 27 (270°), 30 + 100 = 130 knots.

What Do the Special Codes Mean?

Two codes appear regularly and are worth memorizing before your checkride.

9900 means light and variable. The wind at that altitude is essentially calm or shifting without a consistent direction worth encoding.

A missing entry at 3,000 feet for a given station means that altitude is within 1,500 feet of the station’s terrain elevation. Winds aloft are not forecast when the level sits too close to the ground. A station at 2,500 feet MSL will simply have no 3,000-foot data.

How Do You Use Winds Aloft for Groundspeed and Fuel Planning?

The most direct application is groundspeed calculation. True airspeed through the air is fixed by your aircraft. Groundspeed - which determines time en route and fuel burn - depends entirely on the wind component along your route.

A 15-knot headwind in a Cessna 172 cruising at 110 knots TAS reduces groundspeed to roughly 95 knots - about a 14% reduction. That changes time en route, fuel consumption, and whether you arrive with required reserves or need an unplanned fuel stop.

How Do You Pick the Best Cruise Altitude From Winds Aloft Data?

Do not look only at the winds at your planned altitude. Pull two or three adjacent altitude levels and compare them. A 10-knot tailwind at 8,000 feet versus a 5-knot headwind at 6,000 feet is a significant difference - the extra fuel to climb almost always pays back in groundspeed savings.

The Airman Certification Standards for the private pilot certificate expect exactly this reasoning. When an examiner asks why you chose a particular altitude, the answer should trace back to what the winds aloft data showed - not a comfort preference, but an actual comparison of what was available.

There is also a turbulence clue buried in the data. If two adjacent altitude levels show dramatically different wind directions or speeds, that wind shear layer can signal mechanical turbulence between them. It is less direct than a PIREP or AIRMET, but pilots who scan the data carefully are reading information many students walk right past.

How Do You Use the Temperature Column?

The temperature column gets less attention than wind direction and speed, but it matters for two things.

First, density altitude. The forecast temperatures give you specific data to estimate aircraft performance at cruise altitude and at your destination, rather than extrapolating from surface conditions.

Second - and more safety-critical - the freezing level. Scan the temperature column from lower to higher altitudes and find where values cross zero degrees Celsius. If 6,000 feet shows +2°C and 9,000 feet shows −6°C, your freezing level is approximately 7,000 feet. Any visible moisture above that altitude puts you in structural icing conditions.

For VFR pilots this defines the altitude above which clouds carry a hazard on days with significant moisture present. For instrument pilots it is a go/no-go factor. The general aviation accident record involving structural icing is not ambiguous - know the freezing level before departure.

Where Do You Find the Winds Aloft Forecast?

The primary source is aviationweather.gov, the Aviation Weather Center’s public site. Under Products, select Winds and Temperatures Aloft, choose your region and altitude levels, and pull the text-encoded product.

ForeFlight, Garmin Pilot, and most EFB apps integrate winds aloft as a graphical overlay with wind barbs along your route. The tabular text version lets you compare multiple altitudes side by side quickly; the graphical overlay makes direction easier to visualize spatially. Both are worth knowing.

Check the issuance header before using any forecast. The four daily issuance times are 0000, 0600, 1200, and 1800 Zulu. The 6-hour forecast is most accurate. The 12-hour forecast is reasonably reliable. The 24-hour forecast is a planning picture only - confirm with the most current issuance on the morning of your flight.

A standard briefing from Leidos Flight Service (1-800-992-7433) includes winds aloft for stations along your route. Write the values down. If anything looks surprising, ask the briefer - that is exactly what they are there for.

Putting It All Together: A Realistic Altitude Decision

You are planning a 250-mile westbound cross-country from the midwest. METARs and TAFs look fine. Now check winds aloft:

• 6,000 feet: west-northwest at 22 knots - a direct headwind. Groundspeed drops to roughly 90 knots. That is nearly 3 hours for 250 miles.
• 9,000 feet: northwest at 12 knots - significantly better. Temperature is −4°C, placing the freezing level around 8,000 feet. There is scattered cumulus along the route - manageable if you stay clear of tops.
• 12,000 feet: winds shift more northerly and increase to 18 knots - worse than 9,000.

Nine thousand feet is the optimal altitude: better winds than both 6,000 and 12,000, above most afternoon thermal activity, and with the freezing level identified and a plan to avoid cloud tops.

That is the exact reasoning an examiner expects. Not “nine thousand seemed fine” - but “six and twelve showed less favorable winds, and nine gave the best groundspeed with a safe margin below the forecast freezing level given the clouds along the route.” That answer demonstrates you know how to use your weather products.

Key Takeaways

• The Winds and Temperatures Aloft Forecast (FB winds) covers 3,000 to 39,000 feet MSL and is issued four times daily by the Aviation Weather Center at 0000, 0600, 1200, and 1800 Zulu.
• Each entry encodes: first two digits = wind direction in tens of degrees, next two = wind speed in knots, remainder = temperature in °C.
• When direction digits exceed 50, subtract 50 for the true direction and add 100 to the speed - this signals winds of 100 knots or more.
• 9900 = light and variable; a missing 3,000-foot entry means the station sits within 1,500 feet of that altitude level.
• Always compare two or three altitude levels to find the best cruise altitude - wind differences between levels directly affect groundspeed and fuel burn.
• Scan the temperature column to locate the freezing level: visible moisture above that altitude means structural icing conditions.