AIR NAVIGATION Part 2 Distance Speed & Time

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)

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.

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.

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 + - + -

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.

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.

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.

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 + - + -

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.

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.

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

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

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

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

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

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

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

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

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

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

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

AIR NAVIGATION End of Presentation