1. AIR NAVIGATION
Part 4
Magic Numbers

2. Introduction So far we have talked about drawing vectors on paper.
This is fine in the office or the classroom
but impossible in the confines
of a small aircraft.

3. Introduction So for many years, navigators have been using
the Dalton hand held computer,
and these are still used
in the private flying world.

4. Introduction The fast jet navigator in the RAF
solves the vector triangle
using a simplified mental calculation.
In civil airliners an onboard computer
solves the triangle
and many other things besides.

5. Computers and Numbers
All Aircrew have to do a lot of mental arithmetic,
even in these days of computers.
To aid this
Magic Numbers
are used.
It does not matter if you are flying in a Tutor
or a Tornado,
the method works equally well.

6. Computers and Numbers nm per min GS Magic Numbers are ground speeds
in nautical miles per minute.
nm per min GS 60 1
540
480
420
360
300
240
210 9 8 7 6 5 4 3½ 80 1⅓ 90 1½
100 1⅔
120 2
150 2½
180 3

7. Computers and Numbers 10 minutes to run Example Magic Numbers
You are flying at 120 kts GS.
You have 20 miles to run before you reach your
final destination.
How long will this take?
Magic Numbers
2 nm/min
120 kts =
( 120 divided by 60 )
20 miles at 2 nm per minute
20 divided by 2 = 10
10 minutes to run

8. Computers and Numbers Example Magic Numbers 7 minutes to run
You are in a Tornado at low level
over Wales doing 420 kts GS.
You have 49 miles to run to the next turning point.
How long will this take?
Magic Numbers
7 nm/min
420 kts =
( 420 divided by 60 )
49 miles at 7 nm per minute
49 divided by 7 = 7
7 minutes to run

9. How long will a 20 mile leg take?
Computers and Numbers
Example
You are on a cross-country exercise
in a Tutor, heading into wind at 80 kts GS.
How long will a 20 mile leg take?
Magic Numbers
1⅓ nm/min
80 kts =
( 80 divided by 60 )
20 mile leg 20 20 x 3 4 = = 1⅓ 4 3 1 5 20 x 3 4
5 x 3 = 15 min =

10. 6 Minute Magic With the slower speeds
it is often easier to think in terms of
how far do we go in 6 minutes
(1 tenth of an hour).
This is simply the ground speed
with the last zero removed.
Ground Speed 10

11. 6 Minute Magic So the Tutor doing 80 knots,
will travel 8 miles in 6 minutes.
Travelling at 110 knots,
You go 11 miles in 6 minutes.
An aircraft doing 140 knots.
will travel 14 miles in 6 minutes.

12. 6 Minute Magic Despite all the computers,
some mental arithmetic is essential,
whether you plan to join the RAF as aircrew,
become an airline pilot, obtain a PPL,
or simply make the most of the available
air experience opportunities.
The starting point is the 6 times table;
no one in their right mind would dream of
aviating without this knowledge.

13. E T A Estimated Time of Arrival (ETA) A by-product of solving
the Triangle of Velocities
is that by making the DST calculation
using Ground Speed and Distance To Go,
we can calculate the time that it will take
to reach the next turning point or destination.
This time is called
Estimated Time of Arrival (ETA)

14. E T A The Estimated Time of Arrival (ETA)
is important both for fuel calculations
and for Air Traffic control purposes.
A particular application of this is
the ETA for the destination.
If you do not arrive on time,
Air Traffic will have to take overdue action;
similar to a search party going out
to find a group of walkers
who have not returned from a trek on time.

15. still used by navigators in private flying?
Check Understanding
What is the name of
the hand held computer
still used by navigators in private flying?
Dalton
Newton
Dawson
Nelson

16. Check Understanding 2 mins 6 mins 10 mins 20 mins
Flying at 240 kts ground speed,
how long will it take to cover 40 nm ?
2 mins
6 mins
10 mins
20 mins

17. Check Understanding 120 kts 150 kts 180 kts 210 kts
While flying you cover 3 nm every minute,
What is your ground speed?
120 kts
150 kts
180 kts
210 kts

18. how far will you travel in 6 minutes?
Check Understanding
In a Tutor doing 80 knots,
how far will you travel in 6 minutes?
6 nm
8 nm
10 nm
13⅓ nm

19. Check Understanding Fuel calculations The shortest route
Estimated Time of Arrival is important.
ETA calculations help the crew to determine . . .
Fuel calculations
The shortest route
Drift corrections
Wind speed and direction

20. Check Understanding No immediate action Close down
An aircraft does not arrive
at its destination on its ETA,
What action will Air Traffic Control take?
No immediate action
Close down
Initiate overdue action
Contact the departure base

21. AIR NAVIGATION
End of Presentation