Transmissometer
An apparatus, normally consisting of a projector and receiver, used to determine visibility by measuring the transmission of light through the atmosphere; it is the measurement source for determining runway visual range (RVR) and runway visibility value (RVV)

Transfer Baggage
Baggage that has been transported on a flight to a certain location, and then is offloaded and transferred to another flight within a defined time period for transportation to another location.
Transportation Index (TI)
A unit of measure used in the calculation of the level of radioactivity associated with a radioactive shipment.

Type Certificate
The certificate issued by an NAA of a state that defines the design of an aircraft type and certifies that this design meets the appropriate airworthiness requirements of that state.
Equivalent Terms: Aircraft Type Certificate Type Certificate Holder
The organisation that has approval by the applicable NAA to design, manufacture, test, and produce a specific aircraft type.
Type Design Organisation
The organisation that has approval from the NAA to design a specific aircraft type.

U
Ultrasonic Inspection
Non-Destructive Testing method involving Ultrasonic techniques. Unaccompanied Baggage
Checked baggage that has been loaded into an aircraft that does not have the owner/passenger also on board.

Un-airworthy
A condition of an aircraft that precludes it from being released to service and flown. Unauthorised Interference
Interference that occurs when any item for transport on an aircraft (e.g. baggage, cargo, mail, stores, catering equipment) that has been accepted for transport by an operator and subjected to security controls subsequently is in contact with a person who has not been screened and/or does not have authorised access to security restricted/sterile areas where such items are stored and handled.
Also, interference related to unauthorised access to passengers, the aircraft and/or property of the operator that are in security restricted/sterile areas by a person who has not been screened and/or does not have authorised access to such restricted/sterile areas.