The VFR Navigation Plan - ATPL 033 — Flight Planning and Monitoring

With the route chosen, the plan becomes arithmetic. This lesson measures the chart and fills in the navigation plan: waypoints worth flying to, courses and distances, the obstacle that sets the minimum altitude and the corrections that protect it, the climb and descent geometry, and finally the wind triangle that turns true airspeed into headings, ground speeds and leg times, all the way to the alternate.

Waypoints worth flying to

A visual waypoint is chosen by how hard it is to mistake, and the criteria stack:

Large — big enough to be seen from the planned altitude, in the visibility actually forecast.
Unique — one lake among fields confirms position; one lake among forty confirms nothing.
Good contrast — a feature that stands out from its background in the season and light of the flight, because a snow-covered runway on a snow-covered plain is no feature at all.
Vertical extent — towers, masts and ridges stay visible when flat features have merged into the haze.

The strongest waypoints combine criteria: a town alone is ambiguous, but a town with a river bend and a mast beside the road is a fix. And a leg is planned to END at such a feature, so every leg finishes with a confirmation rather than a question.

Measuring the chart

Courses are measured as true courses with a protractor against a meridian, taken near the middle of the leg so chart convergence splits its error evenly, and turned into magnetic courses by applying the variation from the chart's isogonals. Distances come from the chart scale, with the latitude graduations as the built-in ruler: one minute of latitude is one nautical mile. Waypoints, turning points, distances and true and magnetic courses are then transferred to the navigation plan, one line per leg. The vertical dimension gets the same discipline: the plan searches a corridor either side of the course (the task states the half-width) for the highest obstacle, sweeping both sides and counting spot elevations as well as obstacle symbols.

The vertical plan

The highest obstacle plus the required clearance gives the true altitude the flight must really have, and the altimeter must be told about the atmosphere before it can promise that altitude. Cold air first: the altimeter over-reads in cold air, so the indication must be raised by about 4% for every 10°C below ISA. Datum next: each hectopascal between the QNH and 1013 is worth about 30 ft, and with a QNH below standard the pressure altitude sits higher than the altitude flown. The same arithmetic runs from a published minimum grid-area altitude when the chart provides one. Climb and descent geometry closes the section: height to gain divided by the rate of climb gives the time, and time multiplied by ground speed gives the horizontal distance the climb or descent will occupy on the chart.

Finishing the plan

Three calculations complete every leg line:

TAS — from the performance data's CAS, corrected for altitude and OAT.
The wind triangle — the crosswind component demands a wind-correction angle into the wind, approximately the crosswind times 60 over the TAS in degrees, and the along-track component turns TAS into ground speed.
The clock — distance over ground speed times 60 gives each leg time, and the accumulated times run down the column to the destination and continue to the alternate, because the fuel plan of the next module is built on exactly those minutes.

Waypoints into the GNSS box

When the plan is loaded into a GNSS flight plan, a significant VFR point that is not in the database is inserted in one of two ways: as a bearing and distance from an existing significant point (the chart gives both, measured exactly as above), or directly by its coordinates, latitude and longitude read from the chart graticule. Either way the entry is checked back against the chart before it is trusted, because a mistyped waypoint flies exactly as confidently as a correct one.

Waypoints worth flying to

Measuring the chart

Check you understood

The vertical plan

Finishing the plan

Waypoints into the GNSS box