User's Manual

SYSTEM DESCRIPTION AND INSTALLATION MANUAL
T
3
CAS/Part No.9005000
Alternate Horizontal Position Sources: Retaining TAWS functionality during
GNSS outage or unavailability provides a safety benefit. It is acceptable and
recommended to incorporate a secondary, non GNSS position source, to provide
horizontal position when the GNSS is not available or reliable.
The minimum External Sensor input accuracies accepted for Aircraft Position
are:
● Phase I (Take Off)
1 NMI
● Phase II (Outside Terminal or final area)
2 NMI
● Phase III (Terminal area)
1 NMI
● Phase IV (Final area)
0.5 NMI
(8) Aircraft Altitude
The T
3
CAS Aircraft Altitude input parameter is updated from an ADC or GPS
source. The T
3
CAS uses (but is not limited to) the following altitude types:
Corrected Barometric Altitude, GPS Altitude- MSL and Uncorrected Barometric
Altitude.
Vertical Position Sources: Vertical position for TAWS may come from a
barometric source such as an altimeter or an air data computer, or from a
geometric source, such as GNSS. GNSS vertical accuracy, at a minimum, must
meet RTCA DO-229D section 2.2.3.3.4. Designs that cross check barometric and
geometric altitude are recommended.
Barometric altitude equipment must be compliant with TSO-C10b, Altimeter,
Pressure Actuated, Sensitive Type, or TSO-C106, Air Data Computer.
The minimum External Sensor input accuracy accepted for Aircraft Altitude is 95
feet (28.956 meters) with 95% confidence.
(9) Navigation Accuracy
When using GPS or FMS data for aircraft position determination, the T
3
CAS uses
the available GPS or FMS signals to determine accuracy of the position
information.
(a) GPS
For a GPS source, the minimum External Sensor input accuracy
accepted is 100 meters (333 feet) for an HDOP (Horizontal Dilution of
Position) of 1.5 with S/A on.
(b) FMS
The T
3
CAS determines the Navigation Accuracy parameter by using the
RNP data value if a valid RNP data is received AND a valid FMS
Discrete Word is received with the Nav Mode set to “High Accuracy”.
For FMS Discrete Word - Type 2, bit 15 indicates high or low navigation
accuracy and is set independently of the navigation mode, bits 16 - 18.
The FMS sets bit 15 (high accuracy) if the estimated error of the FMS
position is less than the phase of flight position accuracy tolerance listed
in Table 4-55. Otherwise the FMS resets bit 15 (low accuracy).
Pub. No. 8600200-001, Revision 004
34-45-29
4-149
04 Nov 2014
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