(e) Rejection of non altitude reporting aircraft by the own aircraft The TCAS does not display "non altitude reporting aircraft" above 15,500 ft MSL.
R **ON A/C 001-049, 101-105,
F. Sensitivity Level The notion of sensitivity level is very important in the TCAS as many of the operating modes depend on it. The TCAS separates the surrounding airspace into altitude layers. A different Sensitivity Level (SL) threshold for issuing advisories is applied to each altitude layer. The sensitivity level is decreased at low altitude to prevent unnecessary advisories in higher traffic densities such as terminal areas. Generally, the level is determined automatically by the TCAS in function of:
-altitude values from the radio altimeter up to 2500 ft AGL
-barometric altitude values in the 2500 ft to 48,000 ft range. TAU values corresponding to each sensitivity level indicate the TA and RA thresholds. The vertical separation thresholds at CPA also vary in function of the sensitivity level for the different types of advisory. The following table summarizes these data:
R 1EFF : 001-049, 051-099, 101-105, 151-199, 1 34-43-00Page 89 1201-209, 1May 01/05 1 1 1CES 1 ----------------------------------------------------------------------| | TAU thresholds | Vertical separation | | | | thresholds | |----------------------------|-----------------|---------------------| | Source | Altitude | SL TA RA | S0 S1 S2 | | Altitude | | | TA RA RA | | | | | prev cor | | | | (sec) (sec) | (ft) (ft) (ft) | |------------|---------------|-----------------|---------------------| | Radio Alt |less than 1000 | 2 20 | 850 | | Radio Alt | 1000-2350 | 3 25 15 | 850 600 300 | | Baro | 2350-5000 | 4 30 20 | 850 600 300 | | Baro | 5000-10000 | 5 40 25 | 850 600 350 | | Baro | 10000-20000 | 6 45 30 | 850 600 400 | | Baro | 20000-30000 | 7 48 35 | 850 700 600 | | Baro |more than 30000| 7 48 35 | 1200 800 700 | ----------------------------------------------------------------------
NOTE : Level 1 corresponds to Standby Mode in which no advisory is
____ generated.
NOTE : This table indicates the threshold based on own aircraft altitude.
____ Each aircraft altitude depends on an hysteresis:
-1000 + or - 100 ft
-2350 + or - 200 ft
-5000 + or - 500 ft
-10000 + or - 500 ft
-20000 + or - 500 ft
-30000 + or - 500 ft For example, to switch from sensitivity level 3 to sensitivity level 2, the altitude must fall below 900 ft. However, to switch from sensitivity level 2 to sensitivity level 3, the altitude value must go above 1100 ft.
(Ref. Fig. 024)
There are two other means of modifying the sensitivity level:
-selecting TA only mode on the ATC/TCAS control unit forces level
2. In this case, intruders of all types are displayed but will not be transformed into RA symbols and no vertical speed modification indications will be issued.
-the ATC/Mode S equipped ground stations may modify the sensitivity level of the aircraft TCAS via the uplink without, however, having the capability to force the Standby Mode. If several ground stations command sensitivity levels, the TCAS logic selects the lowest level. Definition of priority logic:
R 1EFF : 001-049, 101-105, 1 34-43-00Page 90 1 1 May 01/05 1 1 1CES 1
TCAS - Separation into Altitude Layers
Figure 024
R 1EFF : 001-049, 051-061, 101-105, 1 34-43-00Page 91 1 1 May 01/05 1 1 1CES 1
First a sensitivity level based on altitude is selected. Level 2
is selected if the radio altimeter altitude is less than 1000
ft. Level 2 is also selected if own aircraft is configured such
that both CLIMB and DESCEND RAs are inhibited. Level 3 is
selected if the aircraft is above 1000 ft and below 2350 ft AGL.
If the aircraft is above 2350 ft AGL, barometric altitude is
used to select either level 4 (below 5000 ft), 5 (from 5000 to
10,000 ft), 6 (from 10,000 to 20,000 ft), and 7 (above 20,000
ft).
ATC/TCAS control unit input is read by the TCAS computer. If the
pilot has selected Automatic Mode (TA/RA), then the
altitude-based sensivity level will be used in comparisons to
determine the final level.
From all sensitivity level commands, if any, received from
ground stations, the lowest is selected.
If the TA ONLY mode is selected, either manually via the control
unit or by a ground station, the altitude-based sensitivity
level is used for TA thresholds and the RAs are inhibited.
Otherwise, the lowest of all inputs is chosen.
R **ON A/C 051-099,
R F. Sensitivity Level
R The notion of Sensitivity Level (SL) is very important in the TCAS as
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