Glossary of Terms


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U

Ultimate load

Ultimate load. The limit load multiplied by the appropriate factor of safety.


UN number

UN number. The four-digit number assigned by the United Nations Committee of Experts on the Transport of Dangerous
Goods to identify a substance or a particular group of substances.


Unaccompanied baggage

Unaccompanied baggage. Baggage that is transported as cargo and may or may not be carried on the same aircraft with the
person to whom it belongs.


Unburned hydrocarbons

Unburned hydrocarbons. The total of hydrocarbon compounds of all classes and molecular weights contained in a gas sample,
calculated as if they were in the form of methane.


Unclaimed baggage

Unclaimed baggage. Baggage that arrives at an airport and is not picked up or claimed by a passenger.


Unidentified baggage

Unidentified baggage. Baggage at an airport, with or without a baggage tag, which is not picked up by or identified with a
passenger.


Unit load device

Unit load device (ULD). Any type of freight container, aircraft container, aircraft pallet with a net, or aircraft pallet with a net over an
igloo.
Note.— An overpack is not included in this definition.


Upper-air chart

Upper-air chart. A meteorological chart relating to a specified upper-air surface or layer of the atmosphere.


Usability factor

Usability factor. The percentage of time during which the use of a runway or system of runways is not restricted because of the
cross-wind component.
Note.C Cross-wind component means the surface wind component at right angles to the runway centre line.