Glide geometry, wind and reachable options
A cross-country soaring plan must preserve reachable landing options while using the lift actually available. A glider cannot assume an immediate powered climb when lift weakens. Start with current position, height relative to the intended landing area, glider performance, wind and expected vertical air movement. A calculated range is a model result, not proof that the destination is suitable or legally accessible.
Still-air geometry
A stated glide ratio describes horizontal travel per unit of height lost under its conditions. Multiply the available height loss by the ratio using consistent units, then convert distance as required. Height above the current ground is not automatically height above a distant landing field at a different elevation. Keep the arrival-height and traffic-pattern allowance separate from the theoretical distance to zero remaining height.
A nominal forty-to-one ratio does not mean that every combination of speed, loading, contamination and maneuver gives that ratio. A turn, a changed speed or a different atmosphere can change the result. Use the actual polar and approved performance information rather than assume the best published number applies throughout a route.
Wind and sink
At a given airspeed, a headwind reduces groundspeed. A tailwind increases it. The ground glide ratio also depends on the vertical descent relative to the ground, so air-mass sink can reduce reach even when the horizontal wind is favorable. State whether sink rate and speed are expressed in the same units before dividing them.
Speed-to-fly and glide computers combine assumptions about wind, polar, ballast and other inputs. A positive displayed arrival value does not independently validate the inputs or establish freedom from unexpected sink. An appropriate planned margin and continuing checks remain important. This chapter does not specify a universal safety height or an automatic final-glide trigger.
Navigation and alternatives
Pilotage compares visible features with the chart; dead reckoning estimates motion from known information. Magnetic variation and compass deviation are different corrections. Groundspeed and elapsed time can help check progress, but a confident-looking estimate can still accumulate error. Use the actual available aids without losing awareness of terrain, traffic or wires.
Identify fields and airfields that remain reachable under realistic conditions, and reassess their surface, obstacles, slope, wind and approach options. A field that appears large on a map is not automatically suitable on the day. Plan alternatives early enough to avoid a rushed low-level decision. Airspace, notices, traffic and local operating procedures remain separate checks from the aerodynamic calculation.