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APPENDIX 2
LIMITS
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The TCAD only displays intruders equipped with operative
transponders. TCAD provides no indication of traffic
conflicts with aircraft without transponders, or where the
threat aircraft is outside a Secondary Surveillance Radar
(SSR) environment.
AIRFRAME SHADOWING
Microwave energy can be obstructed by the airframes of
both the host and threat aircraft. A shadowing occurs when
the signals must pass around metal structures.
TCAD is designed to operate optimally when the host
TCAD antenna and the threat transponder antenna are in line
of sight. With the TCAD antenna top and bottom mounted,
and with transponder antennas bottom mounted, the optimal
condition generally exists when threats are above, to
approximately 15 degrees below the host aircraft. When the
threat is further below the host aircraft, or during turns,
signals can be attenuated, causing display of greater than
actual iNM. Transponder antenna placement on the threat
aircraft and flight maneuvers also have an effect. Whenever
a detected threat is below the aircraft, consider airframe
shadowing when analyzing the data.
For a threat to remain in the shadowed region, a lengthy and
parallel track between host and threat is necessary, such as
final approach to a runway when the threat is below your
aircraft.
Note: Airframe shadowing does not affect the accuracy of
altitude separation information.
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