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KTA 970/KMH 980 Pilot's Guide
TCAS I OPERATION
TCAS I monitors the airspace surrounding your aircraft by interrogating
the transponder of the Intruding aircraft. The interrogation reply enables
TCAS I to compute the following information about the Intruder:
1. Range between your aircraft and the Intruder.
2. Relative bearing to the Intruder.
3. Altitude and vertical speed of the Intruder, if the Intruder is
reporting altitude.
4. Closing rate between the Intruder and your aircraft.
Using this data TCAS I predicts the time to, and the separation at, the
Intruder's Closest Point of Approach (CPA). Should TCAS I predict that
certain safe boundaries may be violated, it will issue a Traffic Advisory
(TA) to alert the crew that closing traffic is nearby.
TCAS I SENSITIVITY LEVEL
TCAS I separates the surrounding airspace into two altitude layers. A
different sensitivity threshold level for issuing TAs (traffic advisories) is
applied to each altitude layer. Lower altitudes have less sensitive TA
threshold levels to prevent unnecessary advisories in the higher traffic
densities anticipated at lower flight levels, i.e., terminal areas.
TCAS I has two sensitivity levels (SL) which are described in Table 1,
TCAS I Sensitivity Levels. SL A is invoked using the following order of
precedence: (1) when the TCAS I aircraft is below 2,000 feet AGL (if
equipped with radio altimeter) OR (2) when the landing gear is Extended
(no radio altimeter installed). SL B occurs under all other flight condi-
tions. Table 2, Typical Traffic Advisory Conditions for Sensitivity Levels
describes what conditions will cause a TA to be issued. If aircraft is not
equipped with either a radio altimeter or retractable landing gear, TCAS I
will stay in SL B at all times.
Sensitivity
Level
SL A
In sensitivity level A, TCAS I performs surveillance and tracking func-
tions and provides traffic advisories. The conditions for sensitivity
level A are any one of the following:
(1) Own aircraft is in-flight and is below 2,000 feet AGL, if a radio
altimeter is installed.
(2) Own aircraft is in-flight and the Landing Gear is extended, if a
radio altimeter is NOT installed.
Rev 2
TCAS I Theory of Operation and Symbology
DESCRIPTION
6
006-18273-0000
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