Technical Provisions for Mode S Services and Extended Squitter

Appendix A A-43
MB FIELD
1 MSB TRANSMISSION RATE
2
DRAFT - Working Paper ASP TSGWP11-01 for review by the TSG during the meeting in June 2011 in Paris
LSB SUBFIELD (TRS)
3 ALTITUDE TYPE SUBFIELD (ATS)
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30 RESERVED
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Table A-2-7. BDS Code 0,7 — Extended squitter status
PURPOSE: To provide information on the capability and status
of the extended squitter rate of the transponder.
Transmission rate subfield (TRS) shall be coded as follows:
0 = No capability to determine surface squitter rate
1 = High surface squitter rate selected
2 = Low surface squitter rate selected
3 = Reserved
Altitude type subfield (ATS) shall be coded as follows:
0 = Barometric altitude
1 = GNSS height (HAE)
Aircraft determination of surface squitter rate:
For aircraft that have the capability to automatically determine their
surface squitter rate, the method used to switch between the high and
low transmission rates shall be as follows:
a) Switching from high to low rate: Aircraft shall switch from high to low
rate when the on-board navigation unit reports that the aircraft’s
position has not changed more than 10 metres in any 30 second
interval. The algorithm used to control the squitter rate shall save the
aircraft’s position at the time that low rate is selected.
b) Switching from low to high rate: Aircraft shall switch from low to high
rate as soon as the aircraft’s position has changed by 10 metres or
more since the low rate was selected.
For transponder-based implementations, the automatically selected
transmission rate shall be subject to being overridden by commands
received from the ground control.
Draft
DRAFT - Working Paper ASP TSGWP11-01 for review by the TSG during the meeting in June 2011 in Paris