Who decides what measurement units are used for altitude, and why is there no standard?

Question

I know that some countries (Russia and China for instance) use meters to measure altitude while the rest of the world uses feet. Why isn't this standardized around the world?

I guess all modern cockpit instruments nowdays offer both unit system measurements, but this must be creating some confusion for pilots.

Who decides which measurement units should be used for aircraft altitude? The airlines? ATC? Each country?

Why are both units of measure used? Are there any pros or cons with using meters?

Answer 1

Unfortunately, countries tend to want to decide themselves how stuff is supposed to work once you're within their borders. That's why we have different rules and laws, and when you go somewhere else in the world, you might need to know some of the differences.

In England they drive on the wrong side of the road, imagine that! :)

In order to have things run smoothly in something so utterly international as aviation, the organization called ICAO (International Civil Aviation Organization) where most countries of the world are members, dictates the rules, (I believe they are) called the ICAO drafts recommendations which the member states should incorporate into their respective laws and regulations. If they choose not to, they need to inform the ICAO of such deviation, don't know exactly what happens then, but I believe the idea is to at least let everybody know there's a discrepancy.

The ICAO Annex 5 specifies units to use, including units for altitude and actually specifying meters as the primary unit, with feet being accepted as non-SI alternative. Why on earth you'd want to go against the majority on this I don't know, perhaps due to the fact that it's an SI unit and they want to be as much SI as they can. So it's basically up to each country how they want to play it. Most countries stuck with feet.

Answer 2

In response to the pros/cons of feet vs. meters, the big advantage that feet have over meters, is that it allows you to use nice human-memorable numbers for cruising altitudes.

In the US, we generally use 500ft for visual separation, and 1000ft for separating IFR traffic from other IFR. This translates to roughly 150m and 300m respectively. This means, we can explain IFR cruising altitudes as odd-thousands going east, and even thousands going west (up to FL410).

If this were in meters, you'd have to try to explain that going east it's 300m multiplied by odd numbers, and west it's 300m multiplied by even numbers. It's certainly not impossible to figure out in your head, it just isn't as quick and easy. Unfortunately 100m is considered too little separation, and 500m would be an inefficient use of airspace (over-separation), otherwise there might be more of a global push to use meters.

Interestingly, although Russia does use meters, they have actually adopted the international "Flight Levels" (i.e. "climb and maintain FL350" which would be equal to 10650m), so now international flights do not have to change altitude when crossing the border into Russian airspace. However, I believe this is not true for other countries which use meters, such as China, where the separation is typically 300m.

Answer 3

As to feet being the best measurement for height, what utter nonsense! Prior to WW2, all metric countries flew in meters. That changed after WW2 with America dictating what happened on this planet. Unable to convert to the metric system for one reason, big money that has so far thwarted all efforts to accomplish this important task.America forced the almost 80% metric world to fly in stone-age measurements called feet.Well so much for democracy! Maybe China will eventually do the same and force America to go metric! Sure a drastic step, but a well-deserved one!