The Earth
The Solar System & Time
Charts
Using Aeronautical Charts
Basics of Navigation
Distance, Speed & Time
Vertical Navigation
Fuel Planning
Practical Navigation Techniques
Radio Navigation
Practice Exam

Distance

In aviation, the standard units for distance and speed across the Earth are nautical miles and knots:

Distance is measured in Nautical Miles (nm)
Speed is measured in Knots (kts)

A knot is one nautical mile per hour (1kt = 1nm/hr).

The Nautical Mile

One minute of latitude on the Earth’s surface is one nautical mile.
So one degree of latitude is 60nm, since there are 60 minutes (60′) in each degree (1°)

However, the lines of longitude are further apart at the equator and closer together as you move towards the poles. This means the distance between each degree and minute of longitude changes depending on your latitude.

Therefore, one minute of longitude is not equal to one nautical mile.

A nautical mile is slightly more than a statue mile:

1nm = 1.85 kilometres
1nm = 1.15 statute miles
1 minute of latitude = 1 nautical mile
1 minute of longitude does not equal 1 nautical mile

Altitude

The standard unit used for vertical distance and altitude is feet.

1 nautical mile = 6076 feet
1 kilometer = 3280 feet

We can use a navigational computer (such as the CRP-1) to convert between nautical miles, statute miles, kilometres and feet. The navigational computer is talked about in more detail in later lessons, but we will look at how to convert between these units now.

The CRP-1 is the most common Navigational Computer used for the PPL in Europe

On the front face of the CRP-1 there are markers around the outside for nautical miles (NAUT.M), statute miles (STAT.M), kilometres (km), and feet.

Let’s look at an example of how to convert between units using the CRP-1:

Converting Between Distances

Example

What is 3000 feet in metres and in nautical miles?

1 Align 30 on the inner scale with the FEET marker along the outside

2 Without rotating the scale, read off the metres from under the METRES marker along the outside

Under the metres marker is 9.2
We need to know the approximate value to know where to put the decimal point.

In other words: is the answer 9.2m, 92m, or 920m?
There is roughly 3.3 feet in a metre (or 3300ft in a km) so the answer will be roughly 1000m. Therefore, we know the answer must be that 3000ft = 920m

3 Again without rotating the scale, read off the nautical miles from under the NAUT.M marker along the outside

Under the nautical miles marker is 5.
Again, we need to know the approximate value to know where to put the decimal point.

There is roughly 6000 feet in a nautical mile (or 1.8km in a nm) so the answer will be roughly half a nautical mile. Therefore, we know the answer must be that 3000ft = 0.5nm

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