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Cessna 172 Novelist On Weights And Measures

Mon Jun 01, 2009 7:25 pm

I know that English is the international language of aviation.

I'm unclear about weights and measures, however.

In Europe and Asia, are distance, length, elevation, weight, volume, and barometric pressure communicated in SAE or metric units?

For instance, would a European pilot flying over Mont Blanc communicate to his ATC that he's nn,nnnn feet high, or would he say that his elevation is n,nnn meters?

Would he measure temp in Fahrenheit or Celsius?
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RE: Cessna 172 Novelist On Weights And Measures

Mon Jun 01, 2009 8:38 pm

Everywhere except certain countries like China and Russia, speed and altitude is given in knots and feet. When it comes to pressure, weights, volume and temperature, the pilot or airline is free to chose whatever they want, though I suspect temperature and pressure are mostly given in metric untis in Europe.

Basically, all data that is communicated by ATC is standardised, the rest can be chosen to your liking.

Please correct me if I'm wrong!
Exceptions confirm the rule.
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RE: Cessna 172 Novelist On Weights And Measures

Tue Jun 02, 2009 12:10 am

Aviation is a funny area in this regard - often all three systems (US/imperial, metric and nautical) are used at the same time.

As mentioned, pretty much everywhere in the world, altitude/elevation and speed are measured in feet and knots, regardless of whether the country has adopted the metric system or not.

Distances in the context of navigation are always expressed in nautical miles. Makes sense as 1 knot = 1 nautical mile per hour, and knots are always used.

Distances in the context of visibility and runway length etc. can change a little - in Asia and here in Australia we use metres to express these figures. Weight can vary from operator to operator - in many countries, again including the areas of Asia I've seen, and Oz, it's normally kilos. Here, all our flight manuals are in pounds (due to the aircraft being of US origin) and we have approved supplements with official conversions to kilos for our use. With airliners, the manufacturer will configure the aircraft to use the units required by the operator.

Pressure is given in hPa in this part of the world - i.e. ISA sea level pressure is 1013.2 hPa. Can't speak for all of Europe.
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RE: Cessna 172 Novelist On Weights And Measures

Tue Jun 02, 2009 12:55 am

Quoting Zappbrannigan (Reply 2):
Aviation is a funny area in this regard - often all three systems (US/imperial, metric and nautical) are used at the same time.

Indeed. And Roy...if you're after an interesting read on a real-world example of how differing units of measurement can wreak havoc in the world of aviation, I highly recommend Freefall...a book about Air Canada Flight 143.

Best of all, used copies are only one cent!

Intentionally Left Blank
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RE: Cessna 172 Novelist On Weights And Measures

Tue Jun 02, 2009 8:02 pm

In Europe, short distances are in meters, longer distances are usually in nautical miles although kilometers can be seen every once in a while as well. Statute miles are about the only thing not used.

Altitudes are given in feet in most of the world, except for China, Russia and a few other places where they use meters. Military aviation and gliders used meters in my part of the world (N. Europe) until quite recently when the military started using both systems.

Speeds are generally in knots, with some places using km/h AFAIK. And again, the same situation regarding the military and gliders around here.

Vertical speeds are either in feet per minute or meters per second.

Weights are pounds mass or kgs. Fuel is measured by weight or by volume. In the latter case, I've seen litres, US. gallons and imperial gallons.

Regarding altitudes, all altitudes are measured by pressure altitude as compared to a reference pressure. At lower altitudes, this reference pressure is what the pressure would be at sea level, hence giving a correct altitude above sea level. At higher altitudes, where you care more about using the same reference as all others to stay clear of traffic rather than using a true altitude above sea level, you switch to using a standard sea level pressure as your reference pressure. When flying on this reference pressure you do not talk about feets of altitude at all, but rather about flight levels, which are in hundreds of feet. I e 21,000 feet read on the altimeter on a standard altimeter (reference pressure) setting would be FL210. Your Mont Blanc example may or may not be into the flight levels. Of course gliders and military aviation tend to care more about their altitude above the place where they land and take off, using the Mk. I eyeball for traffic and terrain avoidance, so they often use a reference pressure setting giving an altitude of 0 feet when landing on the runway.

If you state location, aircraft type and country of origin of the intended outfit I think we'll be able to have a long, interesting and possibly informative argument about the units to use in here.  Wink

Confusing? Yes, indeed. In a former job, I used kg-inches, pound-meters and pound-millimetres a lot. Go figure.  Smile

I'd state with confidence that we are at least not using fathoms per forthnight for anything, unless I was certain that someone would pop up and tell me that company so-and-so in some remote corner in fact have their altimeters calibrated according to this standard...
I thought I was doing good trying to avoid those airport hotels... and look at me now.

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