直升机飞行训练手册 HELICOPTER FLIGHT TRAINING MANUAL(36)

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PREPARING THE CHART
Once you have selected the appropriate current aeronautical chart(s) and decided on the route, draw the “required track” lines from the point of setting heading through intermediate points to the destination, and determine the true tracks and distances. The required track lines should be drawn in a way that makes them easily distinguished from printed chart detail and yet does not hide chart features. A highlighter pen can be used to emphasize the track line drawn on the chart.
Determine distances, then examine the route carefully and note the following:
1. elevation of terrain, with particular attention given to hills, peaks, ATSs, hydro lines, and other obstructions;
2. danger and prohibited areas;
3. other aerodromes and/or landing sites; and
4. location, availability, and distances between checkpoints.
To assist in assessing in-flight deviations from track and making corrections, drift lines could be drawn on the chart. These are lines drawn on the chart at 10 degrees each side of the required track line from both the set heading and destination points. They are described in detail later in this text, but can be seen drawn on the chart in Figure 20-1. A preferred set-heading point is an easily identifiable or known landmark, such as a railway or road intersection, a bend in the river, a ATS, a small village or lake, to which the pilot can “eye ball” his way to set heading. Accuracy on setting heading is essential. Setting heading from the downwind leg is not acceptable if the track line originates from the centre of the heliport symbol on the chart, as a half to 1 mile track error could exist from the start.
For rapid distance calculations, the track line drawn on the chart should also be marked into 10 miles intervals (Fig 20-1). Another method is to strike a line across the quarter, mid, and three-quarter waypoints of each track segment. Both these chart-marking systems are to aid mental time, distance, and track error calculations.
 
 

 
Figure 20-1: Chart preparation using 10-degree lines
THE FLIGHT PLANNING FORM
As information relating to the proposed flight is accumulated, enter it in the appropriate sections of a flight planning form. Figure 20-2a shows how the planned flight from Melfort to Humboldt would be entered. The cruise altitude of 4,500 feet, and true airspeed, track, and wind velocity can be entered, and the remaining figures can be added as they are obtained through measurement or calculation. Other pertinent information, particularly weather and landing details, can be added for current and future use.
 

 
Figure 20-2a: Flight planning form 
TRACK LINE MEASUREMENT
One of the properties of a Transverse Mercator Projection is that scale can be considered constant all over the chart. Because of this the meridians of longitude, (the vertical lines), converge at a point above the top of the chart, and for that reason a straight line drawn on the chart meets each meridian at a slightly different angle. To offset these differences, place the protractor at the midpoint of the track line when measuring that angle. This is particularly important when the track line is long and runs parallel to the parallels of latitude.
AIRSPEED CORRECTIONS
True Airspeed (TAS) is used for navigation computations since indicated Airspeed (IAS) varies with temperature, pressure, and altitude. Conversion of IAS to TAS (or vice-versa) can be done very rapidly on your circular navigation computer. Because most helicopter operations are conducted at relatively low altitude, quite often IAS is used, as the differences are minimal.
WIND VELOCITY (W/V)
In aviation terminology, the term wind velocity, usually abbreviated to W/V, implies both the direction of the wind and its speed. Wind velocities normally change with altitude and, in planning a cross-country flight, this must be taken into account when preparing the flight planning form. Many factors affect the selection of the altitude(s) at which a flight will be conducted and W/V is a major one.
　
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