indicates such action is warranted. SE transferred from a depot or commercial repair activity require hydraulic fluid sampling prior to transfer. TRCODE—Transaction Code or Technical Directive Code. TSN—Time Since New. TSO—Time Since Overhaul. TURNAROUND—The time between arriving at a point and departing from that point. TURNAROUND CYCLE—Used in conjunction with vehicles, ships, and aircraft and comprising the following: loading time at home, planned maintenance time, and, where applicable, time awaiting facilities. TURNAROUND INSPECTION—An inspection conducted between flights to ensure the integrity of the aircraft for flight, verify proper servicing, and to detect degradation that may have occurred during the previous flight. TYCOM—Type Commander. TYPE MAINTENANCE CODE—A one-character numeric or alphabetic code that identifies the type of maintenance performed. WSE—Weapons Support Equipment. UAV—Unmanned Aerial Vehicle. UIC—Unit Identification Code. UNSCHEDULED MAINTENANCE—Mainte- nance, other than the fix phase of scheduled main- tenance, occurring during the interval between scheduled downtime maintenance periods. UPKEEP—The preventive, restorative, or additive work performed on aircraft, equipment, and SE by the operating units and aircraft SE activities. The term applies to any method of processing aircraft required to ensure the completion of standard operating periods or service tours, including, but not limited to the servicing, periodic inspections, functional and bench test, replacement, preservation, modification, and repair. An upkeep process extends from the time some of the work is started until all the work is completed, including temporary interruptions in direct labor; it also includes upkeep, evaluation, test, and correction of discrepancies determined thereby. Upkeep is divided into two categories: standard and special. WUC—Work Unit Code—A one-, three-, five-, or seven-character numeric or alpha/numeric code. It identifies a system, subsystem, set, major component, repairable subassembly, or part of an end item being worked on. WUCs are assigned and controlled by NATEC under the direction of COMNAVAIRSYSCOM and published in WUC manuals for end items in three major categories: (1) T/M/S for aircraft, drones, and missiles; (2) aircraft flight/tactical trainers; and (3) aeronautical SE. The system code is the first two positions of the WUC and is used to identify the system within the aircraft/equipment on which work is being performed. These codes are found in the applicable WUC manual. AI-26 VIDS/MAF—Visual Information Display System/ Maintenance Action Form—A multi-purpose document used in the MDS and VIDS. ZONAL INSPECTION—A general inspection of a specific area of aircraft or SE at a scheduled interval. These inspections are for obvious defects, such as leaks, frayed cables, cracks, corrosion, or physical damage. Zonal inspections are normally performed in conjunction with other scheduled maintenance tasks by the rating assigned. For example, an AT rating assigned to perform an inspection on a radar antenna might also be assigned a zonal inspection of the entire compartment for obvious defects. WD CODE—When Discovered Code—A one- character alphabetic code that identifies when the need for maintenance was discovered. WEAPON SYSTEM—A  weapon  and  those components/parts required for its operation. (The term is not precise unless specific parameters are established.) WEAPONS TEST EQUIPMENT—Specialized equipment of an electrical or electronic design used to test, maintain or service aircraft weapons, bombs, rockets, missiles, special weapons, torpedoes mines, or any other explosive ordnance. This equipment is a category of WSE. WORK CENTER CODE—A three-character code that identifies work centers. They are used in MDR to identify a work center performing the maintenance action documented. WORK CENTER SUPERVISOR—The person assigned the responsibility of maintenance management within a given work center. WRA—Weapons Replaceable Assembly.