Home' RTCA Documents for Review : ACAS X MOPS DRAFT Vol.1 Contents 32
ACAS X MOPS
B, ADS-R and TIS-B. These systems include subsystems for surveillance data
processing (ASSAP), and display and control (CDTI).
Air Traffic Control (ATC) - A generic term for a joint civil-military system for
controlling traffic within a specific area.
Air Traffic Control Radar Beacon System (ATCRBS) - A secondary surveillance radar
system having ground-based interrogators and airborne transponders capable of operation
on Modes A and C.
Alert - A flight deck indication meant to attract the attention of and identify to the
flightcrew information relevant to collsion avoidance .
Altitude Crossing - Encounters in which two aircraft are intended to cross or actually
cross in altitude prior to reaching closest point of approach.
Altitude Crossing RA - A resolution advisory is altitude crossing if it is based on an
intention to resolve the risk of collision by crossing in altitude prior to reaching closest
point of approach. In a multi-threat encounter, each threat is considered separately.
Altitude, Relative - The altitude of the intruder aircraft measured from the ownship
aircraft, i.e., relative altitude is positive when own is lower and negative when own is
higher (Relative Altitude = Intruder Altitude – Ownship Altitude)
Altitude Separation - The absolute value of relative altitude.
Bearing - The horizontal angle of an intruder aircraft relative to the nose of the ownship
aircraft, sometimes expressed as a clock position measured clockwise.
Broadcast – Unsolicited transmission to a non-specific destination.
Cancel Vertical Resolution Advisory Complement (CVC) - Information sent from one
Active CAS-equipped aircraft to another via a coordination interrogation to cancel the
Vertical Resolution Advisory Complement (VRC) previously sent.
Closest Point of Approach (CPA) - The occurrence of minimum range between own
ACAS aircraft and the intruder. Thus, range at closest approach is the smallest range
between the two aircraft and time of closest approach is the time at which this occurs.
Coasted Track - A track that is continued based on previous track characteristics in the
absence of surveillance data reports.
Cockpit Display of Traffic Information (CDTI) – A subsystem of the ASA System that
provides the flight crew interface. The CDTI subsystem includes the actual display
media and the necessary controls to interface with the flight crew. Thus the CDTI
consists of all displays and controls necessary to support the applications. The controls
may be a dedicated CDTI control panel or it may be incorporated into other controls,
(e.g., multifunction control display unit [MCDU] or Electronic Flight Bag [EFB]).
Similarly, the CDTI display may be a stand-alone display or displays (dedicated
display(s)) or the CDTI information may be present on an existing display(s) (e.g., multi -
function display) or an EFB. At a minimum, CDTI includes a graphical plan-view (top
down) traffic display, in these MOPS referred to as the Traffic Display, and the controls
for the display and applications (as required).
Collision Avoidance - The third layer of conflict management, whereby aircraft in
imminent risk of colliding are given traffic situation awareness and possibly maneuvering
guidance to avoid a mid-air collision.
Collision Avoidance System (CAS) – The combination of aircraft, pilot (when pilot is
present), avionics, and procedures working together to perform the function of collision
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