Units and conversions

Navigation · Chapter 5 · DGCA CPL and ATPL

How to work the ASA CX-3 for distance, speed, time and fuel, and how to change any distance, speed, volume or mass into the unit you need.

Remember

The exam computer is the ASA CX-3: FLT, ▼ to the function, ■; type each value and =; read the ? lines. C clears the whole function.
1 NM = 1.852 km = 1.15 SM; 1 m = 3.28 ft.
m/s × 1.944 = kt; km/h ÷ 1.852 = kt.
1 imp gal = 4.546 L, 1 US gal = 3.785 L; 5 imp = 6 US.
kg = litres × SG; lb = kg × 2.2046; fuel = flow × time.

Your exam computer: the CX-3

The only computer in the exam • The DGCA exam uses the ASA CX-3 electronic flight computer • No slide rule, no CRP-5: you pick a function, type what you know, read the answer • Watch it work out 150 kt for 40 minutes
Open a function • FLT shows the E6-B list • ▼ steps down the list; the orange ■ opens the one you want • Ground Speed is the 7th line: FLT, ▼ ×6, ■
Fill in the lines • Type a value and press =: a green ✓, and the cursor jumps to the next line • Orange ? lines are what it will work out • When the inputs are in, the answers appear by themselves
Hours and minutes • Times go in with the : key: 0:40 is 40 minutes, 1:45 is 1 h 45 • No need to change minutes into decimals
Set your units first • A new CX-3 starts in US units: °F, US gallons, pounds, inches of mercury • On a line, SET UNIT changes it: °C, litres, kg, hPa. Do it before the exam: it remembers

Miles, kilometres and feet

Why so many units • Navigation uses NM and knots; height is in feet • Runways and visibility are often in metres, fuel in kg, lb, litres or gallons • Different countries and aircraft use different ones: a wrong unit is a real danger, so convert with care
One of each, to scale • 1 km < 1 SM < 1 NM • nautical mile 1 852 m · statute mile 1 609 m
Where 1 852 comes from • 1 NM = one minute of latitude • Equator to pole: 90° × 60 = 5 400 NM, about 10 000 km
One distance, three numbers • 250 NM: the same road in each unit • Smaller unit → more of them
Feet and metres • Heights are in feet: 1 m = 3.28 ft • 1 000 ft = 305 m · 1 NM = 6 080 ft