AIR NAVIGATION
Part 1
Distance Speed & Time
LEARNING OUTCOMES
On completion of this unit, you should:
– Be able to carry out calculations to
determine aircraft distance, speed and time
– Understand the principles of vectors and the
triangle of velocities to establish an aircraft’s
track and ground speed
LEARNING OUTCOMES
– Understand the principles of the 1 in 60 rule
– Understand the types of compass systems
used for air navigation, how they work and
their limitations
– Know the hazards that weather presents to
aviation
RECAP
• Latitude/Longitude grid divides the surface of the
Earth into degrees and minutes
• One minute of latitude represents one nautical
mile (nm)
• 1 degree of latitude (60 minutes) equals 60nm
As a complete circle is 360°
then 360 x 60 gives the circumference
of the Earth as 21600 nm
(approx 25000 statute miles).
• Lines of Longitude are sometimes referred to as
MERIDIANS
• When recording your position – the line of
Latitude must be given first.
• The starting point goes through Greenwich and
is referred to as the:
“Prime Meridian”
Finding Distance Between 2 Points
• Use a ruler and dividers
• If you do not have any equipment, using the
marks along the edge of any piece of paper
Change of Latitude
• If two places are on the same meridian then it is
possible to calculate the distance between them
rather than having to measure it
• For example Torrejon airfield (near Madrid in
Spain) is due south of RAF St Athan. These two
latitudes are N40º29’ and N51º24’
• How would we calculate the distance between
them?
Calculation
First Latitude:
N 51º 24’
Second Latitude:
N 40º 29’
Subtracting gives:
10º 55’
To convert 10º 55’ into nautical miles:
10º multiply by 60 = 600
Add the 55’
= 655 nm
Aircraft Speed
• The speed for cars, motorcycles and other landbased vehicles:
– Miles per hour
• For aircraft, the speed is a measure of:
– Nautical Miles per hour – (Knots)
Aircraft Speed
• We cannot use a speedometer to record aircraft
speed.
• The aircraft flies through the air.
• We use an instrument called an Air Speed
Indicator (ASI)
Aircraft Speed
• ASI measures the
dynamic air pressure
• Dynamic Air Pressure is
the pressure caused by
forward motion of the
aircraft
A simplified ASI
Aircraft Speed
• In forward flight the
pressure above the
diaphragm will consist of
Dynamic + Static.
• Below, the pressure is
just Static
• The two static pressures
cancel out and the
diaphragm will move due
to the dynamic pressure.
A simplified ASI
Aircraft Speed
• The movement due to dynamic pressure is
amplified and displayed on the instrument as
Indicated Air Speed (IAS), reading in knots.
Corrections
• The reading on the ASI can be in error because
of two errors, namely Pressure Error and
Instrument Pressure.
• Instrument error is caused by poor
manufacturing tolerances when the instrument
was built.
Corrections
• Pressure Error previously known as position is
caused by sensing incorrect values of static
pressure due to the position of the static vents
relative to the airflow around the aircraft.
• Both errors can be measured by testing the
aircraft under controlled conditions and a
calibration card with the combined errors is
displayed in the cockpit next to the instrument.
Calibrated Air Speed
• Once the two errors have been accounted for,
we are left with Calibrated Air Speed (CAS),
formerly known as Rectified Air Speed (RAS).
• IAS ± Pressure Error ± Instrument Error = CAS
• Thus an IAS of 118 kts with a correction on the
calibration card of +2 kts would give a
CAS of 120 kts.
True Air Speed (TAS)
• To obtain True Air Speed (TAS) from CAS you
need to correct for air density changes caused
by changes in temperature and altitude.
• This can be done by calculation or by
Navigation Computer.
TAS
• If you are flying at speeds greater than 300 kts,
then you need to apply a correction for
Compressibility Error, which is caused by air
becoming compressed in the Pitot Tube.
CAS ± Density Error + Compressibility Error = TAS
Units of Time
• Time is probably the only example of scientific
measurement where every nation uses the
same units.
• Everyone is familiar with days, hours and
minutes; it is only necessary to ensure that you
use hours when working with knots as this
speed is nautical miles per hour.
Units of Time
• In military and commercial aviation the 24 hour
clock is used, set to Greenwich Mean Time GMT
or Coordinated Universal Time (UTC) as it is
now known.
• UTC can also be known as Zulu Time
• Summer Time or Daylight Saving Time is always
ignored.
Calculation of Time of Flight
(Still Air)
• If a car travels 120 miles at 60 mph, it will take 2
hours to complete the journey.
• This is calculated using the distance speed time
formulae
Provided 2 quantities are known
From Speed Distance and Time
The 3rd one can be calculated using the
following formula
Calculation Triangle (Still Air)
Distance
Speed
Time
SPEED (S) =
TIME (T) =
DISTANCE (D)
TIME(T)
DISTANCE (D)
SPEED (S)
DISTANCE = SPEED (S) x TIME (T)
Example:
How fast must we go to cover
1500 nm in 5 hours?
Quantities known are:
Distance
Time
Therefore we use the following formulae:
SPEED (S) =
Therefore:
S (Knots) =
DISTANCE (D)
TIME(T)
3
1500 nm
5 hours
1
= 300
One degree
of latitude
represents:
Check
of Understanding
1 nm
6 nm
60 nm
360 nm
Glasgow is due north of Plymouth
(approximately on the same meridian).
If Glasgow is latitude 55°50’ and
Plymouth is latitude 50°25’
what distance are the two places apart?:
450 nm
525 nm
275 nm
325 nm
55° 50’
-
50° 25’
55 – 50 = 5
5 x 60 = 300
50 – 25 = 25
300 + 25 = 325nm
In the RAF, aircraft speeds are
generally expressed in:
metres per second
miles per hour
nautical miles per second
Knots
An ASI has an instrument correction factor of
+3 kts and a pressure correction factor of -1 Kts.
If the instrument reads 130 kts what is the CAS?
130 Kts
132 Kts
133 Kts
134 Kts
IAS ± Pressure Error ± Instrument Error = CAS
130 kts + 3 kts – 1 kts = CAS
133 kts – 1 kts = CAS
132 kts = CAS
A Tornado is flying at a TAS of 400 kts.
How far will it travel in 2 hrs?
200 nm
200 Km
800 nm
800 Km
DISTANCE = SPEED (S) x TIME (T)
D = 400 kts x 2 hrs
D = 400 x 2 = 800
Kts = Nautical Miles per hour
800 Nautical Miles
800 nm