Aviation Terms
| Title | Description |
| U | Uniform |
| Uncontrolled Airspace | Aviation term to describe airspace where an Air Traffic Control (ATC) service is not deemed necessary or cannot be provided for practical reasons. According to the airspace classes set by ICAO both Class F and Class G airspace are uncontrolled. It is the opposite of controlled airspace. |
| Undershoot | To bring an aircraft down well short of a runway threshold or planned spot while trying to land. Opposite of overshoot. |
| Unicom | A multi-purpose radio frequency used at most non-tower airports as the Common Traffic Advisory Frequency. UNICOM is also used for placing fuel orders, parking instructions, etc. |
| Universal Time (UT) | Modern and correct name for Greenwich Mean Time (GMT). Also called Zulu time. |
| Unoccupied Flight Time | Flight time used in repositioning the aircraft back to its base or the point of passenger enplanement. |
| Useful Load | The weight of the crew, passengers, fuel, baggage and ballast, generally excluding emergency or portable equipment and ordnance. |
| UT1 | The local time at the 0 meridian passing through Greenwich, England; it is the same everywhere. |
| UTC- Coordinated Universal Time | Greenwich Mean Time updated with leap seconds. |
