Why ADS-B Out?

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Randall45

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Randall
I realize ADS-B is difficult to understand (or at least seems as such and deters proper understanding). But my question is this: Why are aircraft required by 2020 to implement ADS-B out? What information does this provide? Because on ADS-B in aircraft, I can see any aircraft who has an operating transponder. So it seems as if the radar/transponder system is already nicely paired with ADS-B. If you can get position and altitude from aircraft that don't already have this feature, what more could you possibly ask for?

Edit: Doing some research. Is it the case that ADS-B out broadcasts similar to VHF in that it doesn't need to first be relaid to a ground station, synthesized, and then rebroadcasted? Like a radio call it would go to an ATC receiver and directly to other aircraft?
 
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Without ADSB out, the picture you get is someone else's. You'll see nothing outside radar coverage, which excludes a hell of a lot of airports, even many Class D's.

Transponders do not broadcast position. ADSB out does. You depend on primary radar for position otherwise. And it has a lot of holes and shadows at low altitude where you need it most.
 
What MAKG said...without ADS-B out on your plane, you only get a partial picture of traffic. Not to mention (even though I'm mentioning it), that you would be able to operate IFR without ADS-B out come 2020. If you have a King transponder and a WAAS GPS for position source, this can be a transponder replacement with the King KT74 or Trig TT-31 for about 3K. Over 5 years that's about $50/month or the cost of eating out one night a month. If you own a plane, it's literally peanuts.
 
The reason the FAA is mandating ADSB-out by 2020 is because as part of the NextGen ATC system, a portion of the current primary radar network will be decommissioned. ADSB-out (each aircraft self-reporting its GPS position) is what replaces the primary radars in those airspaces. Even in areas where primary radar is still in use, NextGen/ADSB is supposed to allow for closer spacing between participating aircraft and thus more efficient use of congested airspace.

The whole bit of not providing TIS-B data to non-participating aircraft is just a carrot to help encourage adoption of ADSB-out earlier so everybody doesn't wait until Dec 31, 2019 before reluctantly calling their avionics shop.

https://en.wikipedia.org/wiki/Next_Generation_Air_Transportation_System
https://www.faa.gov/nextgen/
 
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in general, ADS-B out uses a GPS position source to broadcast the aircraft's position. This position is more accurate than a position derived from ground-based ATC radars (and it is updated more frequently).

ADS-B could be particularly useful in areas of poor ATC radar coverage
 
In a nutshell:

ADS-B out increases the accuracy of horizontal position indicated on ATC radar map very much like how altitude encoders increase the accuracy of vertical position.

The other things we don't see is:

A radar facility is extremely expensive to install and maintain but an ADS-B station only costs a small fraction of that. (I heard $200k for the ADS-B station, no idea how accurate that is)
 
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bnt83 said:
In a nutshell:

ADS-B out increases the accuracy of horizontal position indicated on ATC radar very much like how altitude encoders increase the accuracy of vertical position.
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Minor point, but for the vast majority of air traffic control radar (which are two dimensional radars), a xpdr MODE C doesn't improve vertical position accuracy - it provides it. Without the MODE C you get no altitude info.

Precision approach radars and some military air search radars are 3D and are able to provide the vertical info without a xpdr.
 
Fearless Tower said:
Minor point, but for the vast majority of air traffic control radar (which are two dimensional radars), a xpdr MODE C doesn't improve vertical position accuracy - it provides it. Without the MODE C you get no altitude info.

Precision approach radars and some military air search radars are 3D and are able to provide the vertical info without a xpdr.
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What a resident ADS-B expert was saying, based on which DO-XXX spec a box meets, the information transmitted may not be the current position of the airplane but a predicted location in effort to reduce the latency error, which could be rather large if you are going Mach 6.
 
bnt83 said:
What a resident ADS-B expert was saying, based on which DO-XXX spec a box meets, the information transmitted may not be the current position of the airplane but a predicted location in effort to reduce the latency error, which could be rather large if you are going Mach 6.
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Interesting.
 
Because the FAA made big promises to "modernize" so they can claim that there are benefits, and is insisting on it even if it provides no more information to ATC than my mode C already does.

And, if ADS B is going to replace radar, why do I still need a transponder?

OK - I admit that the latency issue is a really big deal for my LSA flying at 70 knots. It could be, like, several feet!

There is a claim that ATC and reduce separation and pack more airplanes in a given space - so, does anyone know exactly how much can ATC reduce the separation between IFR and VFR traffic in class E airspace?
 
Capt. Geoffrey Thorpe said:
Because the FAA made big promises to "modernize" so they can claim that there are benefits, and is insisting on it even if it provides no more information to ATC than my mode C already does.

And, if ADS B is going to replace radar, why do I still need a transponder?

OK - I admit that the latency issue is a really big deal for my LSA flying at 70 knots. It could be, like, several feet!

There is a claim that ATC and reduce separation and pack more airplanes in a given space - so, does anyone know exactly how much can ATC reduce the separation between IFR and VFR traffic in class E airspace?
Click to expand...

The FAA did the something similar for vertical separation in the 1980s. To fly in RVSM airspace your aircraft must be on an FAA approved RVSM inspection program (as in an RVSM manual signed by your local FSDO) and you must hold a letter of authorization from that FSDO to use it which is NOT transferrable (when the airplane is sold).


Now the FAA is going after horizontal position standards.
 
It's so they can track our every move and bill us accordingly.
 
bnt83 said:
The FAA did the something similar for vertical separation in the 1980s. To fly in RVSM airspace your aircraft must be on an FAA approved RVSM inspection program (as in an RVSM manual signed by your local FSDO) and you must hold a letter of authorization from that FSDO to use it which is NOT transferrable (when the airplane is sold).


Now the FAA is going after horizontal position standards.
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No, seriously, how much improvement in separation can the FAA provide from my VFR LSA in class C/D/E - what is the air space system getting for my $4000.00?
 
Everyone knows that right now you MUST have an antenna on the bottom for ADS-B out, but in the future (unknown which category aircraft) some, if not all, will require an antenna on the top. ADS-B tracking right now is done via ground stations but WILL BE SATELITE BASED too eventually.
 
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This is the advancement in technology that everyone loves to complain isn't happening. There have been small gains in airframes and power plants but leaps have been going on in avionics for decades.
 
Capt. Geoffrey Thorpe said:
There is a claim that ATC and reduce separation and pack more airplanes in a given space - so, does anyone know exactly how much can ATC reduce the separation between IFR and VFR traffic in class E airspace?
Click to expand...

Given all the near-misses lately, I don't think *current* separation is working particularly well. All the accurate reporting in the world will not solve a problem with ATC mistakes.
 
bnt83 said:
This is the advancement in technology that everyone loves to complain isn't happening. There have been small gains in airframes and power plants but leaps have been going on in avionics for decades.
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This true, and the ancient idea that a complex and expensive TSO is required to get accurate position reporting is a holdover of the last generation of avionics.

Generals always prepare to fight the previous war, the FAA always prepares for the previous generation of technical innovation. :mad2:
 
bullwinkle said:
This true, and the ancient idea that a complex and expensive TSO is required to get accurate position reporting is a holdover of the last generation of avionics.

Generals always prepare to fight the previous war, the FAA always prepares for the previous generation of technical innovation. :mad2:
Click to expand...

Think "committe"
 
Capt. Geoffrey Thorpe said:
No, seriously, how much improvement in separation can the FAA provide from my VFR LSA in class C/D/E - what is the air space system getting for my $4000.00?
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Below 10,000', ADSB is not required in class D or in class E (unless you're flying offshore in the Gulf of Mexico).
 
Jim_R said:
Below 10,000', ADSB is not required in class D or in class E (unless you're flying offshore in the Gulf of Mexico).
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If only that were true.
It's also required if you are flying inside the 30nm ring of death around class B - even in the E and G airspace. And when you live right in the heart of the ring, and the nearest airport outside the ring is an hour drive away...
 
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The amount of information transmitted out via ADS-B is a lot more than a transponder obviously. It also including your destination if you punch it into the GPS. I don't remember the number of bits, but it is a substantial increase.
 
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Fearless Tower said:
Interesting.
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1) The aircraft must transmit its geometric position no later than 2.0 seconds from the time of measurement of the position to the time of transmission. (2) Within the 2.0 total latency allocation, a maximum of 0.6 seconds can be uncompensated latency. The aircraft must compensate for any latency above 0.6 seconds up to the maximum 2.0 seconds total by extrapolating the geometric position to the time of message transmission.
(3) The aircraft must transmit its position and velocity at least once per second while airborne or while moving on the airport surface.
(4) The aircraft must transmit its position at least once every 5 seconds while stationary on the airport surface.

The ADS-B out transmitter totally eliminates the need for interrogation by a radar facility and that latency error. The above specs further decrease error.


At 60 miles from the antenna how many times per minute is regular transponder interrogated? 30?
 
Geico266 said:
The amount of information transmitted out via ADS-B is a lot more than a transponder obviously. It also including your destination if you punch it into the GPS. I don't remember the number of bits, but it is a substantial increase.
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(1) The length and width of the aircraft;
(2) An indication of the aircraft's latitude and longitude;
(3) An indication of the aircraft's barometric pressure altitude;
(4) An indication of the aircraft's velocity;
(5) An indication if TCAS II or ACAS is installed and operating in a mode that can generate resolution advisory alerts;
(6) If an operable TCAS II or ACAS is installed, an indication if a resolution advisory is in effect; That's pretty interesting that these will be broadcast automatically IMHO. I'm guessing this requires a TCAS upgrade to interface the separate boxes.
(7) An indication of the Mode 3/A transponder code specified by ATC;
(8) An indication of the aircraft's call sign that is submitted on the flight plan, or the aircraft's registration number, except when the pilot has not filed a flight plan, has not requested ATC services, and is using a TSO-C154c self-assigned temporary 24-bit address;
(9) An indication if the flightcrew has identified an emergency, radio communication failure, or unlawful interference;
(10) An indication of the aircraft's “IDENT” to ATC;
(11) An indication of the aircraft assigned ICAO 24-bit address, except when the pilot has not filed a flight plan, has not requested ATC services, and is using a TSO-C154c self-assigned temporary 24-bit address;
(12) An indication of the aircraft's emitter category;
(13) An indication of whether an ADS-B In capability is installed;
(14) An indication of the aircraft's geometric altitude;
(15) An indication of the Navigation Accuracy Category for Position (NACP);
(16) An indication of the Navigation Accuracy Category for Velocity (NACV);
(17) An indication of the Navigation Integrity Category (NIC);
(18) An indication of the System Design Assurance (SDA); and
(19) An indication of the Source Integrity Level (SIL).
 
Navigation Accuracy Category for Position (NACP) specifies the accuracy of a reported aircraft's position, as defined in TSO-C166b and TSO-C154c.
Navigation Accuracy Category for Velocity (NACV) specifies the accuracy of a reported aircraft's velocity, as defined in TSO-C166b and TSO-C154c.
Navigation Integrity Category (NIC) specifies an integrity containment radius around an aircraft's reported position, as defined in TSO-C166b and TSO-C154c.
Position Source refers to the equipment installed onboard an aircraft used to process and provide aircraft position (for example, latitude, longitude, and velocity) information.
Source Integrity Level (SIL) indicates the probability of the reported horizontal position exceeding the containment radius defined by the NIC on a per sample or per hour basis, as defined in TSO-C166b and TSO-C154c.
System Design Assurance (SDA) indicates the probability of an aircraft malfunction causing false or misleading information to be transmitted, as defined in TSO-C166b and TSO-C154c.

(i) The aircraft's NACP must be less than 0.05 nautical miles (304 feet);
(ii) The aircraft's NACV must be less than 10 meters per second;
(iii) The aircraft's NIC must be less than 0.2 nautical miles (1215 feet);
(iv) The aircraft's SDA must be 2; and
(v) The aircraft's SIL must be 3.
(2) Changes in NACP, NACV, SDA, and SIL must be broadcast within 10 seconds.
(3) Changes in NIC must be broadcast within 12 seconds.
 
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Capt. Geoffrey Thorpe said:
Because the FAA made big promises to "modernize" so they can claim that there are benefits, and is insisting on it even if it provides no more information to ATC than my mode C already does.

And, if ADS B is going to replace radar, why do I still need a transponder?

OK - I admit that the latency issue is a really big deal for my LSA flying at 70 knots. It could be, like, several feet!

There is a claim that ATC and reduce separation and pack more airplanes in a given space - so, does anyone know exactly how much can ATC reduce the separation between IFR and VFR traffic in class E airspace?
Click to expand...

ADS-B is not going to replace radar. All the primary radars are being kept and at most half of the secondary radars will be eliminated. All of the secondary radars in the major terminal areas will be kept. Radar will be used during times of outages of GPS and to detect spoofing of the system. The FAA also indicated that it would not save money over an all radar solution. All of this was clearly stated in the 2010 Final Rule document, but the claim about radar being replaced still comes up over and over.:mad2:
 
Randall45 said:
I realize ADS-B is difficult to understand (or at least seems as such and deters proper understanding). But my question is this: Why are aircraft required by 2020 to implement ADS-B out? What information does this provide? Because on ADS-B in aircraft, I can see any aircraft who has an operating transponder. So it seems as if the radar/transponder system is already nicely paired with ADS-B. If you can get position and altitude from aircraft that don't already have this feature, what more could you possibly ask for?

Edit: Doing some research. Is it the case that ADS-B out broadcasts similar to VHF in that it doesn't need to first be relaid to a ground station, synthesized, and then rebroadcasted? Like a radio call it would go to an ATC receiver and directly to other aircraft?
Click to expand...

Randall,

In most areas with ADS-B In only, you will be lucky to see 5% of the traffic that represents a mid air collision threat. You may see tons of traffic, it just won't be relevant.
 
Fascinating.

Any truth to what that one guy said about transmitting your "direct to"? Seems a bit much and I haven't heard that anywhere.
 
So, will ATC eventually stop asking us to "IDENT" since they can clearly see our tail # on the screen?

Actually, they should have been able to see this for a while with Mode S.
 
dans2992 said:
So, will ATC eventually stop asking us to "IDENT" since they can clearly see our tail # on the screen?

Actually, they should have been able to see this for a while with Mode S.
Click to expand...

Even before that, for IFR we were assigned a transponder code. The Ident feature is included in the ADS-B Out. I assume Ident is used to point out your location on their display.
 
bnt83 said:
1)
At 60 miles from the antenna how many times per minute is regular transponder interrogated? 30?
Click to expand...

The distance from a secondary radar is irrelevant. Terminal radars will typically have a 5 second sweep, and so will interrogate an aircraft 12 times per minute. A long range radar will typically have a 10-12 second sweep, thus interrogating an aircraft 5 or 6 times per minute.
 
John Collins said:
ADS-B is not going to replace radar. All the primary radars are being kept and at most half of the secondary radars will be eliminated. All of the secondary radars in the major terminal areas will be kept. Radar will be used during times of outages of GPS and to detect spoofing of the system. The FAA also indicated that it would not save money over an all radar solution. All of this was clearly stated in the 2010 Final Rule document, but the claim about radar being replaced still comes up over and over.:mad2:
Click to expand...

A potential beauty of ADS-B is for areas without radar coverage (e.g., mountainous or oceanic).

Until the lack of message validation is addressed, that potential will remain unachievable.
 
When I was at the Potomac Tracon a year ago, they indicated that only a very small percentage of GA was equipped with ADS_B Out. When I had an Out failure a couple of months ago, I was concerned and monitoring. It came back on 45 minutes later; however, when I asked the NYC controller, to verify that it was back on and he said he did not have the equipment to let me know. I did get the my N # back on my iPad display. I was surprised by the controller's admission.
 
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