Nerd question: ADS-B emergency flags

Message Topic Search Topic Options Post Reply Create New Topic Printable Version Translate Topic

   Last
 night our local flying club had its quarterly safety meeting. One of 
the speakers is part of the team equipping US Army fixed-wing aircraft 
with ADS-B, and he dropped a few factoids in his presentation that I 
didn't know before.

One was that the standard set of ADS-B Out parameters (there are 19 
of 'em in case you were curious) includes an "emergency" flag. This may,
 but does not have to be, set by the transmitter when an emergency is 
indicated. See FAR 91.227(d)(9).
 This is formally known as the "Emergency / Priority Status Selection" 
or EPSS, and it uses a type code of 28, so I'll just call it TC28.

What I'm curious about is which GA transponders actually transmit 
this flag. I haven't found a regulatory requirement that the transponder
 emit a TC28 message when the pilot selects an emergency squawk code. Does the AXP series do this? 

Author	Message Topic Search Topic Options Post Reply Create New Topic Printable Version Translate Topic
paulr Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 24 Jan 2014 Status: Offline Points: 558	Post Options Post Reply Quote paulr Report Post Thanks(0) Quote Reply Topic: Nerd question: ADS-B emergency flags Posted: 28 Jun 2019 at 11:54am
	Last night our local flying club had its quarterly safety meeting. One of the speakers is part of the team equipping US Army fixed-wing aircraft with ADS-B, and he dropped a few factoids in his presentation that I didn't know before. One was that the standard set of ADS-B Out parameters (there are 19 of 'em in case you were curious) includes an "emergency" flag. This may, but does not have to be, set by the transmitter when an emergency is indicated. See FAR 91.227(d)(9). This is formally known as the "Emergency / Priority Status Selection" or EPSS, and it uses a type code of 28, so I'll just call it TC28. What I'm curious about is which GA transponders actually transmit this flag. I haven't found a regulatory requirement that the transponder emit a TC28 message when the pilot selects an emergency squawk code. Does the AXP series do this?

paulr Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 24 Jan 2014 Status: Offline Points: 558	Post Options Post Reply Quote paulr Report Post Thanks(0) Quote Reply Posted: 02 Jul 2019 at 9:17am
	The requirement to do this is covered both in the FAR and in AMOC. So I am going to guesstimate that the AXP340 meets this requirement.. but I'm sure not gonna test it on my own! 14 CFR § 91.227 - Automatic Dependent Surveillance-Broadcast (ADS-B) Out equipment performance requirements ... (d) Minimum Broadcast Message Element Set for ADS-B Out. Each aircraft must broadcast the following information, as defined in TSO-C166b or TSO-C154c. The pilot must enter information for message elements listed in paragraphs (d)(7) through (d)(10) of this section during the appropriate phase of flight. ... (9) An indication if the flightcrew has identified an emergency, radio communication failure, or unlawful interference; And the AMOC: AC 20-165B 3.7.3.2 Emergency Status The installation must provide a means for the pilot to enter the emergency status of the aircraft. Although TSO-C166b and TSO-C154c identify multiple emergency codes, only the codes for general emergency, no communications, and unlawful interference are required to be available for broadcast. It is acceptable to base the ADS-B emergency status on the emergency status code input into the transponder (that is, Mode 3/A codes 7500, 7600, and 7700). Refer to section 3.7.3.5 of this AC for information on single point of entry of the emergency status.

AviSteve Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 12 Feb 2018 Location: Melbourne, FL Status: Offline Points: 2274	Post Options Post Reply Quote AviSteve Report Post Thanks(0) Quote Reply Posted: 03 Jul 2019 at 8:46am
	Yes, AXP340 is compliant with DO-260B, which specifies "The Extended Squitter Aircraft Status Message (TYPE Code=28)"
	Steve Lindsley Avidyne Engineering

paulr Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 24 Jan 2014 Status: Offline Points: 558	Post Options Post Reply Quote paulr Report Post Thanks(0) Quote Reply Posted: 03 Jul 2019 at 8:57am
	Thanks, Steve. The speaker painted this capability as optional, not a requirement, which I think is incorrect based on my reading. He also said a couple of other things that turned out upon research to be wrong too, so I guess I won't be asking him for any more avionics advice.