As marine-and aviation-charts are marked with lines of latitude and longitude, this makes estimating distances and speeds rather easy. Turns out each nautical mile equals one second of latitude, which therefore means each minute (60 seconds, you’ll recall) of latitude equals 60 nautical miles. Plus, you’ve got to give it to the globe-trotting sailors as they’ve worked out a good system using nautical miles. Well, the military uses both ships and airplanes in common operations, so a universal measurement would seem expedient in their line of work, which might explain why they started using knots. Why did knots ever come to aviation anyway? It is, after all, a measure of nautical miles traveled, which by the sound of it shouldn’t have much to do with piloting aircraft. The result is we sport aviators converse to this day in a mixture of knots and miles. In the later 1970s knots entered the general aviation world in a meaningful way, this after taking over commercial and military aviation in the decades prior along with ultimately stillborn attempts to align the United States with international standards. At that point Mach numbers became more useful to the fast movers, so that part of aviation added “Mach 1,” “.82 Mach” and so on to the lexicon. We can perhaps start by observing that from the beginning in English speaking countries, namely England and the United States, aviation speeds were universally given in miles per hour-that is, statute miles per hour-up to the jet age. Still, a brief examination of the situation shows just how confusedly human we remain. In other words, both knots and miles are acceptable in aviation, or when in Rome…(use kilometers). Oh, the ICAO can recommend all they want, but to the horror of concrete-specific personalities worldwide, the convention is we all have to get along as each of us uses the measurements most comfortable to us. That’s because, like all bottomless debates, there is no authority supreme enough to decree we’re all going to use one measurement over another. If there ever was grist for the mill, the prop wash surrounding the units of measure regarding aircraft speed is it. To put it politely, we were recently taken to task for using mph instead of knots when reporting on an aviation speed record because, among other things, “mph is for cars not aeroplanes.” Digital instrumentation is a godsend to speed measurement agnostics as the units can be toggled between knots and mph.

Speed of sound in knots