Typical Changes
Refers to the nominal aircraft characteristics.

U
Ultra High Frequency The set of frequencies between 300 MHz and 30 GHz. Ultra High Frequency Crosslink Ultra High Frequency link between satellites. Uncertainty / Doubt The extent to which you have confidence in the machines' decision on when and how to intervene and support the task. Uncertainty Area (MTCD) An airspace buffer around a system trajectory to allow for deviations of the aircraft from the system trajectory. Uncertainty Phase A situation wherein uncertainty exists as to the safety of an aircraft and its occupants. Uniform Without variation and appearing the same to the end user regardless of location. Unit Endorsement An authorisation associated with a rating and where appropriate rating endorsement(s), stating the sectors and/or operational positions for which the rating is valid. Universal Time Co-ordinated An atomic time scale is the basis for civil time. It is occasionally adjusted by one-second increments to ensure that the difference between the uniform time scale defined by atomic clocks, does not differ from the Earth's rotation by more than 0.9 seconds. Unknown Traffic A radar blip or RPS observed on a radar display which cannot be related to any aircraft known to be operating in accordance with an ATC clearance, or under an approved procedure not requiring prior ATC clearance. Unusual Incidents The project will provide training on unusual situations for ATCOs. The examples will deal with a set of agreed scenarios. Extensive use of video and frequent interactions will make this package attractive and suitable for continuation training. Updated Airspace Use Plan An ASM message of NOTAM status issued by an AMC on the day of operation to update AUP information. Uplink A term referring to the transmission of data from the ground to an aircraft. Mode S ground-to-air signals are transmitted on the 1,030 MHz interrogation frequency channel. Upper Air Control Centre An air traffic control unit responsible for the separation of aircraft in a defined segment of airspace in the higher altitude levels, usually above 23,000 feet.

Tip: to find a specific term, use the Acrobat search : click U on the binocular icon in the window bar menu
Upper Control Area A controlled airspace extending upwards from a specified flight level without an upper limit unless one is specified. Upper Flight Information Centre A flight information centre serving upper airspace. Upper Layers A term pertaining to the session, presentation and application layers of the OSI reference model. Usability Applies to systems. Means whether a system is easy to learn, pleasant to use, error-free and error-forgiving, easy to remember and efficient. Usability Engineering Comprises a number of methods and techniques to ensure that a system is easy to learn, pleasant to use, error-free and error-forgiving, easy to remember and efficient. User Users refer to the aggregate of organisations, people, automated systems, infrastructure, procedures, rules and information, which receive services from the EATCHIP Phase III ATM System, but are not part of it (i.e. not owned and/or operated by the EATCHIP Phase III ATM System). There are two major categories of Users : aviation users and non-aviation users. The term "Aviation users" refers to the aircraft operators. Typical examples of Non-aviation Users are : physically or functionally adjacent Air Navigation Systems, air defence, law enforcement agencies, customs, etc. User Application Profile Essentially defines, for a given ASTERIX application, which of the catalogued Data Items will be used, their length (where applicable), their assignation to the Data Fields and possible specific communication requirement. User Class The notion of Class of User is defined with respect to a possible service limitation that the User will accept in case of e.g. ARTAS overload conditions. User Range Accuracy The one-sigma estimate of user range errors in the navigation data for each individual satellite. It includes all errors for which the space or control segment is responsible. It does not include any errors introduced at the user set. User Range Error Estimated error in range due to factors such as unmodelled atmospheric effects, orbital calculation errors, satellite clock bias, multipath and selective availability. Utility The relative value of an outcome with respect to a set of other possible outcomes. (CDSEPT, 1996).