Elements of AIR NAVIGATION

Chapter 18.2

Theoretical Background

The comprehensive knowledge of VFR-navigation instruction includes the following theoretical knowledge and
practical applications:

• flight preparation

• interpretation of current meteorology and weather forecasts (METEO)

• flight planning, establishment of a navigation flight plan (NFP)
  

• fuel calculation

• filing of an ATC flight plan for the Air Traffic Management (ATC FPL)
  

• flight performance calculation (PERFORMANCE)

• RTF-procedures
  

• visual navigation procedures and by means of electronic aids
  

• procedures in special situations
  

By using these basic theories you are able to perform the navigation flights provided for in visual flight conditions. You acquire the knowledge in a theoretical course according to the official syllabus.

Determination of a Position

by the name of the place:

This is simple and limited and is only possible in a known area.

Determination of a Position

Using the Geographic Coordinate System:

For the purposes of mapping, the terrestrial globe is divided into a lattice of 360 degrees longitude and 180 degrees of latitude:

Determination of a Position

Using the Geographic Coordinate System:

Each position on the Earth can be designated by coordinates, that is, by the intersection of a longitude with a latitude and by a finer division in minutes and seconds of an angle.

Example:

Orientation

Orientation: direction, course

Orientation consists of determining the direction of movement of the aircraft and its position in relation to known points. Orientation, direction determination and route establishment may be expressed according to two systems: by means of the compass or by means of the wind rose.

Both systems have the North as a baseline and they are divided as follows:

the wind rose is simplified for the AIR NAVIGATION, it is divided into eight cardinal points.

the compass scale has 360 degrees

Orientation

Orientation; direction, course

In navigation, we use the compass and the wind rose as follows:

The wind rose (cardinal points) is used to indicate general directions in relation to an orientation point.

Compass scale (numbers) indicates directions or headings

Example:
The heading on the compass from A to B is 270°

Orientation

Relative angle

The reference line for direction is the longitudinal axis of the aircraft, which is called the HEADING.

The angle between the longitudinal axis of the aircraft and an orientation point is a REALTIVE ANGLE.

The term «relative» refers to the longitudinal axis of the aircraft as the starting point of the measurement

Orientation

Relative Angle

Direction along the longitudinal axis of the aircraft

270° to the WEST

Relative Angle with the orientation point (mountain) approx.

+ 40°

The mountain is located at approx.

310° north west

Course Indications

The course and heading information is always given with three digits, for example: for the route 030 we say, «zero three zero».

TRUE COURSE, TC

Definition:

the true course is the angle between the straight line connecting two points of the coordinate system and the north pole.

Course Indications

Variation / VAR

VARIATION is the local difference of angle between the geographic north (TN) and the magnetic north (MN):

The course in relation to the geographic north is a TRUE COURSE

The course in relation to the magnetic north is a MAGNETIC COURSE.

Distance and Time

Conversion Factors:

Procedure for calculating the estimated flight time between two points / ESTIMATED ELAPSED TIME, EET

Distance in 1 minute

To calculate the time / distance at the departure or the approach it is useful to know how far the aircraft is traveling in one minute. The values which result from this calculation can be easily memorised.

At a speed of 60 KTS the airplane travels in 1 minute 1 NM
At a speed of 90 KTS the airplane travels in 1 minute 1.5 NM
At a speed of 120 KTS the airplane travels in 1 minute 2 NM
At a speed of 150 KTS the airplane travels in 1 minute 2.5 NM

Distance and Time

Basic Factor

For distance / time-of-flight calculations, it is convenient to use the Basic Factor. Provided that the distances are measured in NM and the speeds in KTS, the Basic Factor is calculated by a simple division.

Dividing 60 by airspeed gives the Basic Factor. The multiplication of the Basic Factor by the distance in NM gives the EET in minutes.

Distance and Time

The 6-Minute Scale

With the 6-minute scale a distance is calculated that corresponds to 1/10 of the flight speed.

The 6-minute scale is indicated for different flight speeds at the edge of the ICAO aeronautical chart of Switzerland.

Distances measured on the chart can be read on this scale, taking into account the units.

Drift

Drift

The aircraft is diverted from its course by lateral winds, depending on its direction and strength.

Drift

Recognising Drift

Drift can be recognised with the help of two methods:

1. On the flight path, two points that lie behind each other, during flight, will move sideways. You will notice this movement because the nearest point will displace itself relative to the distant point.

Drift

Recognising Drift

The drift can be recognised with the help of two methods:

2. The lateral deviation between the predicted no wind position and the current position allows the drift to be measured by a simple formula:

Drift

Drift Correction / Drift Prevention

To correct the drift, you must fly crabbing into the wind. When the planned route is reached again, the correction includes two values:

• the correction to recover the desired route calculated in advance
  

• wind correction

The magnitude of the correction required to compensate for the effect of the wind is determined by a triangle of velocities.

TRACK / T

The TRACK is the airplane’s path relative to the ground, taking into account all the effects acting upon it.

Triangle Of Velocities

The triangle of velocities is the basis for dead reckoning (DR) navigation

Triangle Of Velocities

The triangle of velocities is calculated from the drift or from the known wind

Construction by drift:

Triangle Of Velocities

The triangle of velocities is calculated from the drift or from the known wind

Construction based on the known wind:

Triangle Of Velocities

Construction of a Triangle of Velocities

Triangle Of Velocities

Magnetic Heading, MH

The basics for calculating the MAGNETIC HEADING, MH is the geographical course / TRUE COURSE, TC. The TC must be corrected by:

• the variation / VAR. It is indicated on the aeronautical chart by isogones.
  

• the wind correction angle WCA, is calculated from the triangle of velocities.
  

Magnetic Compass, MC

Magnetic Compass, MC

The HEADING, HDG is read under the lubber line of the MAGNETIC COMPASS, MC.

The lubber line corresponds to the LONGITUDINAL AXIS of the aircraft

Deviation Card
The deviation table is a list of small deviations that cannot be compensated for by technical means. It is determined by the COMPASS SWING (process of compensating a compass by determining and reducing the deviation coefficients and recording the residual deviations)

Magnetic Compass, MC

Magnetic Compass Errors

Acceleration (Northern Hemisphere):

The compass tilts and turns during an acceleration or a deceleration. This effect is particularly felt for headings towards the east or the west:

• in acceleration the scale of the compass turns and displays a direction closer to North.
  

• in deceleration (negative acceleration) the scale of the compass turns and displays a direction closer the south.
  

Magnetic Compass, MC

Magnetic Compass Errors

Turning Error (Northern Hemisphere):

When changing direction towards North, the indication of the compass is delayed.

When turning South, it is advanced.

Magnetic Compass, MC

Magnetic Compass Errors

Deviation, DEV

The MC is affected by the ferrous metal parts of the airplane and electrical fields, and the resulting error is called a deviation, which is not the same for all headings. It depends on the direction of flight. The deflection scale table is found in the vicinity of the MC and contains the correction values. For well-compensated instruments the deviations may be negligible. For heading calculations in light aircraft, such deviations are rather theoretical.

Directional Gyro, DG

Directional Gyro, DG

The magnetic compass is difficult to read when turning and during acceleration. The DIRECTIONAL GYRO / DG remains stable even when turning.

The DG is not a compass and must be adjusted according to the MC at regular intervals:

• to compensate for the apparent loss due to the Earth’s rotation
  

• due to errors because of balancing imperfections or friction
  

The importance of the deviation always
depends on the quality of the instrument
and its condition.

Directional Gyro, DG

Directional Gyro, DG

Adjustment of DG is possible only in stabilized straight and level flight.

In cruise flight it must be done every ten minutes.

In the LINE UP CHECK and several other checks the DG is adjusted.

DGs that adjust automatically are called SLAVED GYROS.

Directional Gyro, DG

Representation of HEADING, HDG on the DG

Lateral Navigation / Vertical Navigation / Navigation-Flightplan

Lateral Navigation

Terminology: lateral navigation encompasses direction and distance.

We measure the true course / TC and the distances / DIST on the aeronautical chart:

Vertical Navigation:

Terminology: vertical navigation refers to flight altitude

• Flight altitudes according to AFM performance tables.

• Minimum Altitudes by Aeronautical Chart

Lateral Navigation / Vertical Navigation / Navigation-Flightplan

Navigation-Flightplan