PILOT NAVIGATION
Senior/Master Air Cadet
Learning Outcomes
Know the basic features of air navigation and
navigational aids
Understand the techniques of flight planning
Understand the affects of weather on aviation
Introduction
This portion of the syllabus will now
tie the previous 3 subjects together
Units
Units
At school you will have been taught
that in the modern world everything is
measured in metric units
However in real life many people use non
metric measures. An example of this is the
use of miles & mph in the UK
Units
This unit will look at the units commonly
used for:
vertical distance
weather
aircraft weight
speed
pressure
fuel
Vertical Distance and Speed
In aviation horizontal distances are
measured in nautical miles and speed in
knots
OneThese
minuteunits
of arc
aremeasured
based onatthe
thelength
centreofof
the earth
a “GREAT
equalsCIRCLE”
1 nm on the
on the
earth's
surface
surface
of
the earth
Vertical Distance and Speed
In the vertical axis the majority of countries
use feet to measure height or altitude. Only
the former communist countries use metres
Vertical Distance and Speed
It must be noted that many countries who use
feet have changed their maps to show
elevation in metres, - such as the UK OS maps
Vertical Distance and Speed
Great care is needed because an aircraft
flown in thousands of feet can be in a very
dangerous position
!
if a navigator reads a mountain top at
2000’ when it is 2000 metres which is
about 6000’!
Vertical Distance and Speed
Terrain clearance is done with great
care & the navigators number one
priority
The calculation of the safety altitude
there should be no doubt
Vertical Distance and Speed
Vertical Speed uses the same units as
Vertical Distance
Feet
Vertical Distance and Speed
Vertical speed indicators which show
rate of climb or descent are calibrated in
thousands of feet for most military
aircraft
Meteorological Units
World-wide the met office has changed to
metric units
With the major exception of the USA
However even the met office must
continue to use feet for altitude &
knots for windspeed
Aircraft & Fuel
Strictly
speaking
& fuel
should be
For aircraft
theaircraft
units used
depend
mass
on the measured
country of by
manufacture
In practical terms it is weight
(the
effect
of
gravity
on
mass
)
Most US aircraft (70% of the worlds total )
that
we
use
use pounds or imperial tons. The rest use
kilograms (kg) or metric tonnes
Aircraft & Fuel
For fuel the situation is more complicated
In theory it should be measured by mass
as the amount of thermal energy in one
unit of fuel relates directly to its mass!!!
Aircraft & Fuel
You cannot measure fuel when an aircraft
is in flight, so it is measured by volume,
as in cars.
In cars we measure the fuel volume in litres
(or gallons) & then calculate the fuel use in
km per litre (or mpg )
Aircraft & Fuel
However the use of volume in the air is not
AVTUR
accurate enough as the type of fuel
& the temperature affect the
mass per unit
volume
AVGAS
one type
of fuel isofalways
used,from
its
In Even
other ifwords
the density
fuel varies
density will change
with temperature
type to type
changes
Aircraft & Fuel
Different types of fuel each have a
Specific Gravity ( SG )
This is a Water
measure
between
hasofathe
SGratio
of 1.0
the weight
of the
theof 0.80
A typical
jet engine
fuelfuel
hasand
a SG
weight of the same volume of water
Aircraft & Fuel
This
means aislitre
of by
jet calculator,
fuel weighsa80%
Conversion
done
DR
of the or
weight
of a litre
of RAF
waterflight
computer
the chart
in the
information handbook
Pressure
Several different units are used to
express pressures - according to the
country of origin
Various gasses & fluids in aircraft are
pressurised
Pressure
Our main concern is the pressure in the
atmosphere
The higher we go the less air there is & so
pressure reduces as we gain height
Pressure
Pressure is measured in PSI, Inches of
mercury (US) , in MM of mercury, or millibars
The average (MB)
pressure at sea level
is 1013 MB
Millibars is in general use outside the
USA
Pressure
ALTITUDE
IN FEET
AIR PRESSURE
IN MB
SEA LEVEL
1013
10,000
700
18,000
500
24,000
400
30,000
300
34,000
250
39,000
200
Note
an
aircraft
at
34000’
is
pressurised
to
If it was not for pressurisation all aboard
5000’ and so
the be
amount
of oxygen at that
would
unconscious
height is a quarter of that at sea level
Pressure
At a cruising altitude of 39,000 feet, a Boeing
767's cabin will be pressurized to an altitude
of 6,900 feet¹
¹Commercial Airliner Environmental Control System: Engineering
Aspects of Cabin Air Quality.
http://www.boeing.com/commercial/cabinair/ecs.pdf
Conclusion
Aviation is the only major area of
science still using such a wide variety
of units
Until countries
to common
units to
There
is a slowagree
movement
to metrication
their instruments, and whilst longitude &
latitude remain so will the confusion
Check of Understanding
In aviation how are horizontal distances
and speeds measured?
horizontal distances are
measured in nautical miles
speed in knots
Check of Understanding
How do the majority
measure vertical
distances?
the majority of countries use feet to
measure height or altitude
Check of Understanding
How are Vertical Speed Indicators calibrated?
Vertical speed indicators which show rate of
climb or descent are calibrated in thousands
of feet for most military aircraft
Check of Understanding
In practical terms, how are aircraft
and fuel measured?
In practical terms it is weight
Check of Understanding
What is Specific Gravity?
a measure of the ratio between the
weight of the fuel
and
the weight of the same volume of water