BendixKing KTA 910 System KTA 970 - Manual (Page 21)

KTA 870/KMH 880 Pilot’s Guide
Rev 2 006-18265-0000
13
TAS Theory of Operation and Symbology
Intruders may be seen in surrounding airspace, but not on the TAS
display. The situations in which this may happen are:
•
Most small aircraft have one transponder antenna located on the bot-
tom of the aircraft. When own aircraft is above one of these aircraft,
the transponder antenna can be shaded from the TAS interrogations.
When this occurs, the TAS interrogation may not reach the other air-
craft’s transponder, or the other aircraft transponder’s reply may not
reach TAS’s antenna. A lack of replies prevents TAS from tracking
intruders. Transponder shading also occurs when the other aircraft is
maneuvering such that line of sight to its transponder antenna is
blocked.
•
The TAS directional antennas have a bearing “cone of confusion”.
TAS is able to determine bearings for intruders that are located within
–10 degrees to +70 degrees elevation angle with respect to own air-
craft’s horizontal plane for the top directional antenna (+10 degrees to
–70 degrees for a bottom directional antenna). Intruders that are
located outside of those elevation angles will be tracked with no bear-
ing.
•
TAS is unable to determine bearings for intruder tracked on the bot-
tom antenna when the own aircraft has a bottom monopole antenna
or a bottom directional antenna but the landing gear is extended. In
this case the intruder will be tracked, but not displayed, unless a
Traffic Advisory is issued against it.
•
The other aircraft may have a poor transponder. Ground stations
have more gain and “hear” aircraft at farther distances than TAS.
•
TAS is required to reduce transmitter power when in areas of high
density so that it does not adversely affect (overwork) other aircraft
transponders and prevent the ground ATC from tracking them. This is
known as Interference Limiting (IL). IL can reduce the nominal TAS
surveillance range to around 6 nmi. This means that TAS may not
detect a poorly performing transponder until it is much closer.
•
TAS has a one-second update rate. When in areas of high density,
TAS may reduce its maximum surveillance range to either 10 nmi or
to the range of the 30th intruder in track plus 1 nmi. This allows TAS
to maintain its one-second update rate.
•
TAS has an altitude surveillance volume of –10,000 feet to +10,000
feet relative to own aircraft’s altitude. Any intruders outside this vol-
ume are not a threat to own aircraft and therefore are not tracked by
TAS.