Navigation: Drift, Track and Fuel Planning
What you must be able to do
Balloon navigation is the art of using wind layers. You must understand the triangle of velocities: heading, true airspeed, wind direction and speed, track and groundspeed. Know how to calculate drift and the heading needed to make good a required track, and understand that a balloon's airspeed is essentially the wind, so track is controlled by choosing altitude. Learn how to convert between true, magnetic and compass directions, allowing for variation and deviation, and how to use a map, a chart with airspace overlaid, and a GPS as a cross-check rather than a substitute.
Planning and in-flight technique
Know how to select a launch site with safe access, escape routes, and a landing area within reach of the forecast wind. Understand the concept of a "steerable" flight by climbing or descending into different wind layers, and how to confirm the wind at height using observations, smoke, or other balloons. Learn to estimate groundspeed from map features and time, to keep a dead-reckoning log, and to plan fuel with a reserve. Understand the requirement to remain in radio and radar contact where applicable, and to avoid controlled airspace by a planned margin.
Traps and a rule of thumb
Typical traps: applying variation in the wrong direction, forgetting that groundspeed changes as the wind changes with height, treating a GPS track as a clearance from airspace, and failing to allow for the balloon's inability to hold a heading. Rule of thumb: the 1-in-60 rule - a 1° error over 60 units of distance gives 1 unit of offset; so 5° of drift over 10 NM is about 0.8 NM, which is the margin you should plan against airspace.
Worked example
A balloon tracks 090° at 20 kt groundspeed with a wind of 060°/15 kt at 500 ft and 090°/25 kt at 1,500 ft. To make good 090° at a faster speed, the pilot climbs to 1,500 ft; to slow the drift near a boundary, the pilot descends. This illustrates that altitude selection, not heading, is the primary navigation control.