Airpower Simplified: What is nautical miles, knots and Mach?

There are many aviation terminologies that are being used commonly nowadays, but most people do not understand them. A brief and simplified explanation of some units used by pilots while flying the aircraft or planning the mission is given below.

1.    How Long is a NM? A NM is equal to 1.85 km, 1.5 miles or 6,076 feet. However, the actual historical definition of NM is the reason why it is better suited for naval vessels and aircraft than km or miles.

2.    Historical Definition: NM was based on the length of the arc of 1 minute of equator’s latitude, as 1 degree equals 60 minutes. This means that even without modern technology like GPS, simple charts and maps can be used to measure the distance pretty accurately. If your position has moved by 1 degree, you have travelled through 60 NM. As mentioned above, this makes it a more practical and preferred unit, especially without the modern navigational aids.

3.    Knots: Now that we have grasped the basic concept of NM, we move on to the unit of knots, abbreviated as kts. Again, originally used in maritime navigation, it was adopted for aerial purposes too. Just like a car’s speedometer uses units of km or miles/hr, the Air Speed Indicators (ASI) of aircraft display the speed in knots.

4.    Mach: Unlike knots and NM that have their roots in the sea, Mach is a purely aeronautical speed unit. It is based on the local speed of sound. To put simply, when an object is travelling equal to the speed of sound in any environment, it is said to be at Mach 1, and it becomes ‘supersonic’ above this. Most fighter aircraft have a max speed of Mach 2. (Hypersonic speed is above Mach 5)