Technical Provisions for Mode S Services and Extended Squitter
Technical Provisions for Mode S Services and Extended Squitter
Technical Provisions for Mode S Services and Extended Squitter
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DRAFT - Working Paper ASP TSGWP11-01 <strong>for</strong> review by the TSG during the meeting in June 2011 in Paris<br />
C-20 <strong>Technical</strong> <strong>Provisions</strong> <strong>for</strong> <strong>Mode</strong> S <strong>Services</strong> <strong>and</strong> <strong>Extended</strong> <strong>Squitter</strong><br />
C.2.3.7.3.1.1 “Emergency/Priority Status Message” Broadcast Rates When Transmission<br />
of <strong>Mode</strong> A Code is Disabled<br />
When the <strong>Mode</strong> A Code transmission is disabled as per §C.2.3.7.3.1, the following transmit rates apply:<br />
a. The “Emergency/Priority Status Message” (TYPE=28, Subtype=1) shall be broadcast at r<strong>and</strong>om<br />
intervals that are uni<strong>for</strong>mly distributed over the range of 0.7 to 0.9 seconds relative to the previous<br />
“Emergency/Priority Status” <strong>for</strong> the duration of the emergency condition which is established by any<br />
value other than ZERO in the “Emergency/Priority Status” subfield.<br />
Note.— Emergency conditions resulting from the <strong>Mode</strong> A Code being set to 7500, 7600 or<br />
7700 are covered by the requirements in §C.2.3.7.3.1.2.<br />
b. In the case where there is no emergency condition established by a ZERO value in the<br />
“Emergency/Priority Status” subfield, then the “Emergency/Priority Status Message” shall not be<br />
broadcast.<br />
C.2.3.7.3.1.2 Emergency/Priority Status Message” Broadcast Rates When Transmission<br />
of <strong>Mode</strong> A Code is Enabled<br />
When the <strong>Mode</strong> A Code transmission is enabled as per §C.2.3.7.3.1, the following transmit rates apply:<br />
a. The “Emergency/Priority Status” (TYPE=28, Subtype=1) shall be broadcast at r<strong>and</strong>om intervals that<br />
are uni<strong>for</strong>mly distributed over the range of 0.7 to 0.9 seconds relative to the previous<br />
“Emergency/Priority Status” under the following conditions:<br />
i. For a duration of 24 ±1 seconds following a <strong>Mode</strong> A Code change by the pilot except if the<br />
<strong>Mode</strong> A Code is changed to 7500, 7600 or 7700.<br />
Note.— The case where the <strong>Mode</strong> A Code is set to 7500, 7600 or 7700, the transmission<br />
of the emergency condition is covered by ”ii”. below. Setting the <strong>Mode</strong> A Code to 7500, 7600<br />
or 7700 is indicated by a Permanent Alert in the “Surveillance Status” field (value of 1) (see<br />
Figure C-1). A change in the <strong>Mode</strong> A Code, except to 7500, 7600 or 7700, is indicated by a<br />
Temporary Alert in the “Surveillance Status” subfield (value of 2) (see Figure C-1).<br />
ii. For the duration of an emergency condition by any non-ZERO value in the “Emergency/Priority<br />
Status” subfield, if the emergency code is cleared by the pilot changing the <strong>Mode</strong> A Code to<br />
other than 7500, 7600 or 7700, the broadcast of the “Emergency/Priority Status” Message shall<br />
be continued <strong>for</strong> 24 ±1 seconds as “i” above.<br />
Draft<br />
b. In the absence of conditions specified in “a” above, the “Emergency/Priority Status” Message shall<br />
be broadcast at r<strong>and</strong>om intervals that are uni<strong>for</strong>mly distributed over the range of 4.8 to 5.2 seconds<br />
relative to the previous “Emergency / Priority Status” Message.<br />
C.2.3.7.3.2 Message Delivery<br />
The Aircraft Status (TYPE=28) Emergency/Priority Status (Subtype=1) Message delivery shall be<br />
accomplished using the Event-Driven protocol (§C.2.3.7). The broadcast of this message takes priority over<br />
the Event-Driven protocol broadcasts of all other message types, except <strong>for</strong> the ADS-B Aircraft Status TCAS<br />
RA Broadcast Message (TYPE=28, Subtype=2), which takes priority over the Emergency/Priority Status<br />
broadcast, <strong>and</strong> all other Event-Driven Message types, as specified in §C.2.5.4.3.<br />
C.2.3.8 PERIODIC STATUS MESSAGES<br />
Operational Status Messages <strong>and</strong> Target State <strong>and</strong> Status Messages are Periodic Status Messages that are<br />
broadcast independently in the same manner as the Airborne Position, Surface Position, Airborne Velocity<br />
<strong>and</strong> Aircraft Identification Messages. In previous Editions of this Manual, Operational Status <strong>and</strong> Target<br />
State <strong>and</strong> Status Messages were included under the event-driven protocol <strong>and</strong> subject to the hard limit of 2<br />
transmissions per second in any second as per §C.2.5.4. Analysis is provided that verifies that the<br />
DRAFT - Working Paper ASP TSGWP11-01 <strong>for</strong> review by the TSG during the meeting in June 2011 in Paris