**DISTANCES**

**Nautical Mile**: It is length of an arc of the meridian making an angle of one minute at the centre of curvature at that place.

– ICAO has defined it as a distance of 1852 meters (6080 ft).

– One minute of equator, meridian or latitude is one nm.

– One minute of change of longitude is not 1 nm except at equator.

– Actually the length of 1 nm is variable on the surface of the earth due to ellipticity of the earth. It is 1843 meters at equator, 1853 meters at about 45º N/S and 1862 meters at pole.

**Kilometer:** It is 1/10000th part of average distance from equator to pole on the surface of the earth. It is taken as a length of 3280 ft.

**Statute Mile**: It is a standard length of 5280 ft established by the Royal Decree of British Monarch.

**Conversion of Units of Distances:**

** ** 66 nm = 76 sm

41 nm = 76 km

41 sm = 66 km

1 nm = 1.15 sm = 1.85 km

**Speed:**

**Indicated Air Speed (IAS**): Speed as indicated by the needle on the face of Air Speed Indicator

**Rectified Air Speed (RAS) or Calibrated Air Speed (CAS): **IAS corrected for Position and Instrument error is called RAS or CAS

** ****Equivalent Air Speed (EAS):** It is RAS corrected for compressibility error

– This term is used for speeds 250 nm/h and above where compressibility factor becomes effective.

**True Air Speed (TAS):**

- i) For lower speeds (below 250 nm/h) RAS corrected for density error

is called TAS.

- ii) For higher speed (at or above 250 nm/h) EAS corrected for density error is called TAS.

**Knot**: nm/h is called knot and represented by KT or kt.

Note: 1 To obtain TAS from RAS, Nav computer is used with Pressure Atitude and Corrected Outside Air Temperature (COAT) as inputs.

Note: 2 In the absence of Nav computer TAS may be found by the formula:

TAS = RAS + 1.75% of RAS per thousands of feet.

For example if RAS = 150KT,Pressure Altitude = 10,000ft, then

TAS = 150 + (75/100)x150 x10= 150 + 26.25 = 176.25KT (Approx)

**Mach Number(M):** It is defined as the ratio of TAS to local speed of sound.

M = V/C where V = TAS C = Local speed of sound (C= 39√ TºA)

Example: Given M =0.78, PA = 29000ft. Calculate V.

Solution: ISA temp at F290 is (–29×2+15)-43ºC. TºA= 273-43=230ºA

C=39√ 230=591.46

V=MxC= 0.78×591.46=461.34 say 461kt.

**Kilograms(kgs) and Pounds(lbs**): 1kg = 2.202 lbs