<P> Aircraft altitudes for air traffic control and related purposes are measured in feet in the U.S. In fact, most of the world has used feet for aviation altitudes since the end of World War II (meters before 1945 in all European countries except the UK), with the notable exceptions of China, North Korea, and many CIS (former Soviet) countries . For instance, an airliner on a long flight, even if neither its starting point nor destination are in the United States, might use a nominal cruising altitude of 36,000 feet, using an internationally standardized system of flight levels (Flight Level 360 in this case). In 2011, Russia switched from metric to foot - denominated flight levels at high altitude to eliminate the need for adjustments when crossing in to or out of its airspace . </P> <P> Frequent - flyer programs from commercial airlines in the United States are commonly managed using miles . This is likely to continue; in fact, some international airlines that used kilometers are switching to miles or using both, to simplify the redemption of miles with United States airline partners (Aeromexico switched from kilometers to miles, and Varig from Brazil has used miles since the program was named "Smiles"). Due to influence from the U.S., aircraft speed is often measured in knots and heights in feet in many countries . </P> <P> For both domestic and international routes, U.S. airlines set luggage size and weight restrictions in terms of customary units . Conversely, international airlines that fly to the U.S. often restrict baggage to metric sizes . </P> <P> The temperatures in aviation - related weather reports are given in degrees Celsius in the United States . </P>

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