U

UNINC Unusual Incidents *
UNIX Uniplexed Information and Computing Service
UNL Unlimited
UPD Update Plan Divergence
UPP Upper airspace
UPS Un-interruptable Power Supply
UPSEL Update Selection
UPU Union Postale Universelle (FR) / Universal Postal Union
URA User Range Accuracy *
URANIA Upgrading Athens Terminal Area and Interfacing to the PALLAS ACC system
URD User Requirements Document
URE User Range Error *
URET User Request Evaluation Tool (MITRE Conflict Detection product)
URG Urgency (ICAO)
URP User Requirements Phase
URTF User Requirements Task Force
US/USA United States of America
USAF US Air Force
USAL User Access Level