KTA 970/KMH 980 Pilot's Guide
TCAS I Theory of Operation and Symbology
TCAS I SURVEILLANCE VOLUMES
Surveillance volume is that volume of airspace within which other aircraft
with Mode S or ATCRBS transponders are tracked by own aircraft's
TCAS I. The display volume is controlled by the operator and is not nec-
essarily the same as the tracking volume.
(1) Range Tracking Volumes
The size of the range tracking volume is dependent on whether tracking
is occurring on a directional or OMNI antenna and attenuation levels
applied to the transmitted pulses from the TCAS I processor's transmit-
ter. The typical range tracking volume is pictured as a circle.
The maximum range for TCAS I is 18 nm. However, there are instances
when you may see intruders out to 36 nm. TCAS I reduces range track-
ing volumes in high density areas to reduce the number of receptions to
be processed by TCAS I and for interference limiting. TCAS I can track
as many as 45 aircraft and displays up to 30 of them.
(2) Altitude Tracking Volumes
TCAS I tracks other transponder equipped aircraft that are within a rela-
tive altitude of +/-10,000 feet.
TCAS I AURAL INHIBITS
TCAS I will inhibit the aural annunciation using the following order of
precedence: (1) below 400 ft AGL (if equipped with radio altimeter) OR
(2) when the landing gear is Extended (no radio altimeter installed). For
installations aboard aircraft with fixed landing gear and no radio altimeter
installed, the aural annunciation is not inhibited by the TCAS I processor,
unless weight-on-wheels indicates on the ground. The aural annuncia-
tion is enabled above 600 ft AGL in aircraft equipped with a radio altime-
TCAS I TRAFFIC DISPLAY SYMBOLS
TCAS I will display three different traffic symbols on the traffic display.
The type of symbol selected by TCAS I is based on the Intruder's loca-
tion and closing rate. Relative bearing and distance to the Intruder are
shown by the position of the Intruder symbol in relation to the own-air-
The symbols change shape and color as separation decreases between
your aircraft and Intruders to represent increasing levels of urgency.
The traffic symbols may also have an associated altitude tag that shows
relative altitude in hundreds of feet. A + sign and number above the sym-
bol means the Intruder is above your altitude. A - sign and number
beneath indicates the Intruder is below your altitude. A trend arrow
appears when the Intruder's vertical rate is 500 feet per minute or