How to read a cross-section

A cross-section is a vertical slice of the atmosphere along your planned route — the sky rotated 90° so you can see the layers you'll actually fly through. For a VFR go/no-go, it beats a text GAFOR by a wide margin.

The axes

• Horizontal axis: distance along the route, waypoint to waypoint. Ticks show intermediate legs.
• Vertical axis: altitude in feet, surface to FL100 (10,000 ft). Terrain is drawn as a filled profile — you're flying above the shaded ground.

The cloud heatmap

The blue-to-grey shading is a cloud-cover heatmap: darker = denser cloud at that altitude and position along the route. It's derived from 28 vertical layers of the ICON-D2 model, so you can see where the layers actually are — scattered Cu at 4,000 ft with clear air above, versus a solid overcast up to 6,000 ft, versus a lenticular over the ridge at 8,000 ft — all show as visibly different shapes.

The clearance lines

• VFR clearance line — the lowest altitude at which you clear terrain by the VFR-legal margin along the route (in Germany typically 500 ft AGL over open country, 1,000 ft over congested areas).
• IFR clearance line — the equivalent for the applicable IFR MEA / MSA along the route.

A cruise altitude that stays above both lines and out of the cloud heatmap is the geometric go/no-go answer.

Freezing level

A dashed horizontal line marks the 0°C isotherm. Anywhere the cloud heatmap crosses this line is a potential icing zone — especially for non-de-iced aircraft. Even VMC clear-of-cloud flight above the freezing level is fine; a climb through cloud through this line, in a piston single, is not.

Wind barbs

Wind is drawn as barbs at 8 altitudes: surface, 1,000 ft, 3,000 ft, 5,000 ft, 7,000 ft, 10,000 ft, plus 850 hPa and 700 hPa. Direction is the barb angle; speed is the barb count (5 kt per short line, 10 kt per long line, 50 kt per triangle). This is how you spot wind shear between layers — a >30 kt change over 3,000 ft is worth respecting.

The head/tailwind analysis table

Below the cross-section, a table shows the along-track wind component per leg per altitude. Headwind is red, tailwind is green. The optimal cruise altitude per leg is highlighted — it accounts for wind plus the cloud/terrain constraints from the cross-section above.

Why this beats a text briefing

A conventional GAFOR forecast tells you "Charlie in area 22 between 09:00 and 12:00". That's a scalar warning over a wide area. A cross-section shows you where along your route the Charlie conditions actually sit, at what altitudes, and whether you can climb, descend, or route around them. The same 3-minute look answers three questions a text briefing forces you to guess at.