Pilot/Controller Glossary 

12/2/21 

TRAFFIC PATTERN

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 The traffic flow that is 

prescribed for aircraft landing at, taxiing on, or taking 
off from an airport. The components of a typical 
traffic pattern are upwind leg, crosswind leg, 
downwind leg, base leg, and final approach. 

a. 

Upwind Leg

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 A flight path parallel to the 

landing runway in the direction of landing. 

b. 

Crosswind Leg

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 A flight path at right angles to 

the landing runway off its upwind end. 

c. 

Downwind Leg

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 A flight path parallel to the 

landing runway in the direction opposite to landing. 
The downwind leg normally extends between the 
crosswind leg and the base leg. 

d. 

Base Leg

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 A flight path at right angles to the 

landing runway off its approach end. The base leg 
normally extends from the downwind leg to the 
intersection of the extended runway centerline. 

e. 

Final Approach

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 A flight path in the direction 

of landing along the extended runway centerline. The 
final approach normally extends from the base leg to 
the runway. An aircraft making a straight-in approach 
VFR is also considered to be on final approach. 

(See STRAIGHT-IN APPROACH VFR.) 
(See TAXI PATTERNS.) 
(See ICAO term AERODROME TRAFFIC 

CIRCUIT.) 

(Refer to 14 CFR Part 91.) 
(Refer to AIM.) 

TRAFFIC SITUATION DISPLAY (TSD)

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 TSD is a 

computer system that receives radar track data from 
all 20 CONUS ARTCCs, organizes this data into a 
mosaic display, and presents it on a computer screen. 
The display allows the traffic management coordina-
tor multiple methods of selection and highlighting of 
individual aircraft or groups of aircraft. The user has 
the option of superimposing these aircraft positions 
over any number of background displays. These 
background options include ARTCC boundaries, any 
stratum of en route sector boundaries, fixes, airways, 
military and other special use airspace, airports, and 
geopolitical boundaries. By using the TSD, a 
coordinator can monitor any number of traffic 
situations or the entire systemwide traffic flows. 

TRAJECTORY

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 A EDST representation of the path 

an aircraft is predicted to fly based upon a Current 
Plan or Trial Plan. 

(See EN ROUTE DECISION SUPPORT TOOL.) 

TRAJECTORY

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BASED OPERATIONS (TBO)

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An Air Traffic Management method for strategically 
planning and managing flights throughout the 
operation by using Time

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Based Management 

(TBM), information exchange between air and 
ground systems, and the aircraft’s ability to fly 
trajectories in time and space. Aircraft trajectory is 
defined in four dimensions – latitude, longitude, 
altitude, and time. 

TRAJECTORY MODELING

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 The automated pro-

cess of calculating a trajectory. 

TRAJECTORY OPTIONS SET (TOS)

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 A TOS is an 

electronic message, submitted by the operator, that is 
used by the Collaborative Trajectory Options 
Program (CTOP) to manage the airspace captured in 
the traffic management program. The TOS will allow 
the operator to express the route and delay trade-off 
options that they are willing to accept. 

TRANSFER OF CONTROL

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 That action whereby 

the responsibility for the separation of an aircraft is 
transferred from one controller to another. 

(See ICAO term TRANSFER OF CONTROL.) 

TRANSFER OF CONTROL [ICAO]

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 Transfer of 

responsibility for providing air traffic control service. 

TRANSFERRING CONTROLLER

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 A controller/ 

facility transferring control of an aircraft to another 
controller/facility. 

(See ICAO term TRANSFERRING 

UNIT/CONTROLLER.) 

TRANSFERRING FACILITY

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(See TRANSFERRING CONTROLLER.) 

TRANSFERRING UNIT/CONTROLLER [ICAO]

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Air traffic control unit/air traffic controller in the 
process of transferring the responsibility for 
providing air traffic control service to an aircraft to 
the next air traffic control unit/air traffic controller 
along the route of flight. 

Note: See definition of accepting unit/controller. 

TRANSITION

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 The general term that describes the 

change from one phase of flight or flight condition to 
another; e.g., transition from en route flight to the 
approach or transition from instrument flight to 
visual flight. 

TRANSITION POINT

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 A point at an adapted 

number of miles from the vertex at which an arrival 
aircraft would normally commence descent from its 
en route altitude. This is the first fix adapted on the 
arrival speed segments. 

PCG T

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