1. AIR NAVIGATION
Part 2
Distance Speed & Time

2. RECAP If two places are on the same meridian
then it is possible to calculate
the distance between them,
rather than having to measure it.
We don’t use a speedometer
for aircraft speed.
We use an Air Speed Indicator (ASI)

3. Speed Corrections Instrument Error
ASI readings can be wrong for two reasons –
Instrument and Pressure Errors.
Instrument Error
caused by poor manufacturing tolerances
when the instrument was built.

4. Speed Corrections Pressure Error
ASI readings can be wrong for two reasons –
Instrument and Pressure Errors.
Pressure Error
(previously known as position error)
caused by sensing incorrect values
of static pressure due to the static vents position
relative to the airflow around the aircraft.

5. Speed Corrections - - = CAS
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 + - + -

6. Speed Corrections - - = CAS IAS Pressure Error Instrument Error + +
Thus an IAS (Indicated Air Speed)
of 118 kts
with an overall correction
of +2 kts
would give a CAS (Calibrated Air Speed)
of 120 kts.

7. Speed Corrections To obtain True Air Speed (TAS) from CAS
you need to correct for air density changes
caused by temperature and altitude.
If flying at speeds greater than 300 kts,
you also need to apply a correction for
Compressibility Error,
caused by air being compressed in the Pitot Tube.

8. Speed Corrections - - = TAS When these two corrections have been made,
we are left with
True Air Speed (TAS),
CAS
Density Error
Compressibility Error =
TAS + - + -
Thus a CAS of 120 kts
with a correction of -2 kts
would give a TAS of 118 kts.

9. Speed Corrections - - - - Calibrated Air Speed (CAS), = CAS
SUMMARY
Calibrated Air Speed (CAS),
(formerly known as Rectified Air Speed (RAS))
IAS
Pressure Error
Instrument Error =
CAS + - + -
True Air Speed (TAS)
CAS
Density Error
Compressibility Error =
TAS + - + -

10. Calculation of Time We are all familiar with days, hours and minutes;
But when working with aircraft knots,
it’s only necessary to use hours,
as this speed is nautical miles per hour.

11. Calculation of Time In aviation the 24 hr clock is used,
set to Greenwich Mean Time GMT
or Coordinated Universal Time (UTC)
(also known as Zulu Time)
Summer Time or Daylight Saving Time
is always ignored.

12. Calculation of Time 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
Distance
Speed
Time

13. Calculation of Time Provided 2 quantities are known
the 3rd can be calculated -
Distance (D)
Speed (S) =
Time (T)
Distance (D)
Time (T) =
Speed (S)
Distance (D) =
Speed (S) x
Time (T)
Distance
Speed
Time

14. How fast (in knots) must we go to cover
Calculations
How fast (in knots) must we go to cover
1500 nm in 5 hours?
Distance (D)
Speed (S) =
Time (T) 3
1500 nm (D)
Speed (S) = =
300 kts
5 hours (T) 1

15. How long will it take to travel
Calculations
How long will it take to travel
960 nm at 160 knots?
Distance (D)
Time (T) =
Speed (S) 6
960 nm (D)
Time (T) = =
6 hrs
160 knots (S) 1

16. How far (in nm) will we cover
Calculations
How far (in nm) will we cover
at 270 knots in 3 hours?
Distance (D) =
Speed (S) x
Time (T)
Distance (D) =
270 kts (S) x
3 hours (T) =
810 nm

17. Check Understanding CAS = IAS before corrections
Which of the following statements about
Calibrated Air Speed (CAS),
(formerly known as Rectified Air Speed (RAS))
is true?
CAS = IAS before corrections
CAS = IAS after corrections
CAS always equals IAS
CAS is always less than IAS

18. Check Understanding Altitude and Pressure error
Calibrated Air Speed equals
Indicated Air Speed
with corrections for what?
Altitude and Pressure error
Instrument and Pressure error
Air Density and Pressure error
Compressibility and Pressure error

19. Check Understanding 130 Kts 132 Kts 133 Kts 134 Kts
An ASI has an instrument correction of
+3 kts and a pressure correction of -1 kts.
If the ASI reads 130 kts what is the CAS?
IAS ± Pressure Error ± Instrument Error = CAS
130 Kts
132 Kts
130 kts + 3 kts – 1 kts = CAS
133 Kts
CAS = 132 kts
134 Kts

20. Check Understanding True Air Speed equals Calibrated Air Speed
with corrections for what?
Compressibility and
Altitude error
Air Density and
Pressure error
Compressibility and
Pressure error
Air Density and
Compressibility error

21. Check Understanding 200 nm 200 Km 800 nm 800 Km 800 nm
A Tornado is flying at a TAS of 400 kts.
How far will it travel in 2 hrs?
200 nm
Distance (D) =
Speed (S) x
Time (T)
Distance (D)
200 Km =
400 kts (S) x
2 hours (T)
800 nm
800 Km =
800 nm

22. Check Understanding 15 mins 30 mins 2 hours 4 hours 15 mins
A Tornado is flying at a TAS of 320 kts.
How long will it take to travel 80nm?
Distance (D)
15 mins
Time (T) =
Speed (S) 1
30 mins
80 nm (D)
Time (T) = =
320 knots (S)
2 hours 4
4 hours =
15 mins

23. AIR NAVIGATION
End of Presentation