8/12/2019 GNAV Key Facts

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GNAV - All ()

1) What is the formula for convergency?

Convergency = ch long. x sin mean lat.

2) What is the formula for conversion angle?

Conversion angle = convergency

3) What is a rhumb line?

A line of constant direction and cuts all meridians and parallels at the same angle

4) What is nearer the pole, a rhumb line or a great circle?

A great circle

5) A great circle constantly changes direction, at what point does it have the same direction as a rhumb line?

At the mid-meridian of the track

6) How many NM is 1oof latitude?

60 NM (1 min is 1 NM)

7) What are the fuel conversions?

kg ( x 2.2 ) = lbs

Imp gallons ( x 1.205 ) = US gallonsUS gallons ( x 3.784 ) = litres

litres ( x S.G.) = kg

US gallons ( x 6 ) = lbs

Imp gallons ( x 10 x S.G.) = lbs

8) What are the distance conversions?

1 NM ( x 1.15 ) = SM ( x 1.6 ) = KM

1 inch = 2.54 cm

1 NM = 6080 feet

1 SM = 5280 feet

1 KM = 3280 feet

1 NM = 1852 m

1 NM = 72960 inches (6080 x 12")

9) What is the formula for scale?

Scale = 1 / D = Chart length / Earth distance

10) What is the difference between a large and a small scale?

1 : 250 000 UK chart has a larger scale than 1 : 4 000 000 instructional plotting chart

11) What is the departure formula?

Departure = d.long (in min) x cos mean lat.

12) On a Mercator how does chart convergency relate to Earth convergency?

On a standard Mercator, chart convergency = zero everywhere because the meridians are straight. On the Earth, convergency is only

zero at the equator, therefore at higher latitude, chart convergency has got to be less than Earth convergency

13) On a Lambert how does chart convergency relate to Earth convergency?

At the parallel of origin, chart convergency = Earth convergency and remains constant everywhere on the chart.

On the Earth, convergency is greater at higher latitude and is less at lower latitude.

14) On a Polar stereographic how does chart convergency relate to Earth convergency?

At the pole, chart convergency = Earth convergency and remains constant everywhere on the chart.

On the Earth, convergency is maximum at the pole and zero at the equator.

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15) How do you calculate the time and distance to start a speed reduction for a delayed arrival?

Eg. You are asked to reduce speed from 360 kts to 300 kt and delay arrival by 5 min when should this happen?

i) If you are not given an original ETA, assume one eg. 1000 h

ii) Draw out problem

ETA 1000 h ---------------------------- P

iii) Work out distance travelled at original GS

360 kts x 5 min / 60 = 30 NM (This distance needs to be 'lost')

iv) Work out speed reduction = 360 - 300 = 60 kt

30 NM x 60 / 60 KT = 30 min

v) Arrival has to be delayed by 5 min ie. 1005 h

The time to make the speed reduction is 30 min back from this ie. 0935 h

vi) The distance before the arrival point is 30 min at reduced GS of 300 kts = 150 NM

16) How do you calculate wind velocity when given values for multiple drift?

Set HDG and TAS on the CRP-5

Draw on each drift line in turn

Read off the WV

17) How do you find the vertex?

The longitude is way at the midpoint.

The latitude is found using the formula: Vertex (NM) = (tan CA x departure) / 2

or: Vertex (NM) = CA x departure / 230

18) How do you use unidentified ground features to find aircraft GS?

Eg. An A/C on HDG 032oM, var 9oE with two bearings observed 1000 h Rel bearing 030o, range 100 NM 1015 h Rel bearing 075o,

range 60 NM Work out HDG in true 032oM with VAR 9oE gives HDG 041oT Add the relative bearings to the true HDG and

calculate reciprocals to plot 1000 h 041oT + 030o = 071 + 180 = 251 to plot 1015 h 041oT + 075o = 116 + 180 = 296 to plot Draw

out the problem,

19) How do you calculate polar stereographic tracks?

Eg. An A/C on HDG 032oM, var 9oE with two bearings observed 1000 h Rel bearing 030o, range 100 NM 1015 h Rel bearing 075o,

range 60 NM Work out HDG in true 032oM with VAR 9oE gives HDG 041oT Add the relative bearings to the true HDG and

calculate reciprocals to plot 1000 h 041oT + 030o = 071 + 180 = 251 to plot 1015 h 041oT + 075o = 116 + 180 = 296 to plot Draw

out the problem, How do you calculate polar stereographic tracks? If you have time draw it accurately Draw a circle Identify the

hemisphere Add in W and E (with W on the left of the circle) Apply SCREW or UNSCREW for W0E (which means for the Southern

hemisphere draw out W0E in a clockwise fashion and for the Northern hemisphere draw out W0E in an anti-clockwise fashion) Align

Grid North: UP for Greenwich meridian DOWN for Greenwich Anti-meridian Draw a line to the position of longitude Reposition

Grid North over A/C position Draw in the A/C Grid or True HDG Check where True North is

20) How do you plot a bearing from a VOR?

Take reciprocal if necessary to get QDR Apply variation at station to get QTE to plot using true meridian at station

21) How do you plot a relative bearing to a NDB?

Add aircraft true HDG to relative bearing Apply chart convergency if any Apply variation at aircraft Take reciprocal to get QTE to

plot using true meridian at station

22) How do you plot a RMI bearing to a NDB?

Apply chart convergency if any Apply variation at aircraft Take reciprocal to get QTE to plot using true meridian at station

23) How do you plot bearings using AWR?

Add aircraft true HDG to relative bearing Apply chart convergency if any Take reciprocal Plot using true meridian at position bearing

was taken

24) How are radio bearings represented?

As great circles

25) How is a radio bearing plotted on a Lambert?

How is a radio bearing plotted on a Lambert?

26) How is a radio bearing plotted on a Mercator?

It must be converted to a rhumb line which is a straight line