“It’s a bird. It’s a plane. It’s... more confusion”
The aviation industry is one which holds a special place in my heart, but I won’t bore you with this soppy nonsense. The measurement muddle is truly alive in this industry, so much so, that it makes measurements in Britain seem coherent. Yet still, one of the few global industries manages to work in the midst of a monstrous measurement muddle.
Whilst the language of aviation is standardised to English, there is no such standardisation for units of measurement. Metres, geographical miles, nautical miles, inches of mercury, millibars, knots, metres per second are some of the measurements you are likely to come across if you’re ever in the cockpit.
Let’s start with distances. In the UK, as in much of the world, most distances on the ground e.g. runway lengths, are given in metres. Once you airborne, despite flying being a fairly modern feat of engineering, you go back to the dark ages of measurement. Distances now become nautical miles. (Visibility is in metres or kilometres in most countries, but in geographical miles in North America.)
Once airborne, measuring altitude becomes fundamental. That’s not rocket science. Feet are the most commonly used units globally for altitude, except in a handful of countries, including China. There, they use uses metres. A pilot flying from London to Beijing would start their journey with altimeters calibrated in feet, but have to convert altitudes to metres once in Chinese airspace.
Speaking of calibrating altimeters, this is another minefield. Here there are three sets of units to get used to. Inches of mercury (inMg), hectopascals (hPa) and millibars (mbar) are all used to measure atmospheric pressure (crucial to calculating altitude). Fortunately hectopascal and millibars are both metric and so have the easy conversion of 1=1. But throwing inches of mercury into the mix adds a bit of complexity that nobody really needs. Most countries use hPa, but Japan and the US use inMg. Fortunately most aircraft allow you to easily calibrate aircraft in both.
Wind is also very important for aircraft, a nice tailwind could halve your journey time, and strong crossing could severely affect how you land. Most countries report winds in knots (nautical miles per hour), however a handful use metres per second.
The international civil aviation organisation ICAO (or OACI, as it’s known is its home city of Montreal) had recommended that all aviation uses one set of units. Metric units. That recommendation seems to have been about as effective as a slightly irate mother recommending her teenage son spends less time on the Xbox.
Fortunately pilots are incredibly well trained at all of this stuff and modern aircraft make it very easy to switch between measurements if needed, so there’s no need to be concerned for safety. But the use of a single set of units would be good. The use of only metric units would be even better. We’ll just have to OACI.
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