ads-b for beginners

[sherlock holmes]

While looking at a website called ads-b for beginners, I read the following statement,(Aircraft report their own position via the network and receive back, from the ground system, traffic and other information). This being the case, why when looking at realtime air traffic at my home site do I see tags that are obviously incorrect. If planes are broadcasting their own data then shouldn't it be correct? I have had my RB for a couple years now and I see the blurbs about the databases being updated all the time so I guess I am missing something obvious.

Thanks
Sherlock Holmes

[RodBearden]

Hi Sherlock

It depends which data on the tags you're talking about: data transmitted by the aircraft, or data interpreted by RadarBox databases.

1: Data transmitted by the aircraft may be incorrect because of: miscoding of the ADS-B transmitter hex code (see the Updates thread for many examples of this), inaccurate onboard navigation equipment (especially aircraft not fitted with GPS), and mis-typing by the crew, particularly of Flight ID's. Other avionics problems may cause other problems, such as with heading or vertical rate data.

2: It's possible that if two or more aircraft in the same area transmit simultaneously, the data they send may get mixed up and corrupted and therefore not received correctly by RadarBox. Naturally, in busier areas this problem gets worse. This is also possible if the aircraft is on the very edge of your reception range - the weak signal may not get through correctly.

3: Once the data, accurate or not, has been received by RadarBox, it then has to be interpreted, for example, hex codes into registrations, aircraft types, and owners, and Flight ID's into routes and logos. RadarBox databases do that interpretation, and need to be kept up-to-date. Air Traffic Controllers, we hope, have access to current info, but we, the general public, don't have access to their info, and it all has to be collected and distributed second-hand, so it's possibly late and/or inaccurate.

Our valiant database updaters do a great job with the hex codes, AirNav do their best with routes, and I and other contributors do our best with logos, but it's always a catch-up operation.

As with real life, always treat all information with suspicion. So when you see a Piper Cub at 40,000ft, a flight from O'Hare to Miami somewhere over Tunisia, or an airliner landing a mile away from the nearest runway, don't assume it's the truth (or that it's wrong!).

Hope that helps :-)

Rod

[Chris11]

(Aircraft report their own position via the network and receive back, from the ground system, traffic and other information)

This would be a description of the primary use of ADS-B (Know in the US as NextGen). The concept of ADS-B is that the aircraft will transmit to ground stations. The ground stations would re-transmit all the info to the aircraft. This will allow the aircraft to be fitted with an instrument (screen) that would give the pilot a representation where the other traffic is. This would enhance safety.

While us hobbyists are keen to know who, what, where from, where to the pilot only want to know if the traffic is conflicting.

[Runway 31]

You state that you see tags all the time Sherlock that are clearly incorrect, I dont recall you advising the forum of these and allowing us to ensure the correct information is being displayed or even giving us the opportunity to answer.

In which way is the information incorrect, dont keep these to yourself let us know all know about it and if need be we will correct the info or even advise you that it is correct.  I also presume that you are using the latest published Navdata to ensure that your database is up to date?

The box can only interpret the data sent to it by the aircraft, if the aircraft is sending the wrong data in the first place their is nothing that the box can do about that and will interpret what is sent to it and display it to you accordingly.  We see examples of that all the time, aircraft carrying boxes giving out their previous ID because the new owner hasnt updated them to show their new identity.

Alan

[sherlock holmes]

Hi Rod,
( a flight from O'Hare to Miami somewhere over Tunisia).
This is exactly the kind of mis ID I was referring to in my question. With my minute understanding of ads-b I thought that it was something as simple as a crew inputting their data and it was then transmitted to our receivers. With the large numbers of aircraft in the world changing owners and probably registration numbers (such as automobiles) is it even possible to maintain a database as it seems to be ever evolving and changing? There is no criticism here, just trying to get smarter! Another thing that I noticed on the website was the fact that these broadcast are done in the 1090 megahertz range but that there will also be a 970 megahertz range? Would this mean that a second antenna would be required for this traffic?

Thanks for your time.
Sherlock Holmes

[Runway 31]

Sherlock,

The route data isnt transmitted by the aircraft.  This is gathered from various sources and sent out from the server by Airnav.  This isnt an exact science and evolves all the time as more info is gathered and has nothing to do with the updaters.  The routing info/callsigns etc change at the winter and summer timetables and the routing info taked time to adapt and you tend to get lots of blanks in the routings around he changeover until sufficient data is built up

If it is routing info that you are after there are various threads all over the forum discussing this matter.

You are correct in that the data held regarding aircraft derived from the hex code is ever changing and is a constant task to keep anywhere near up to date but we battle away and do what we can to provide a service.

Alan

[sherlock holmes]

Thanks Alan,
Thanks for the info. It is all very fascinating stuff. When I use my RB at peak times in my own part of the world I may see 20 -25 aircraft on the screen at one time. I've read somewhere that in the U.S. this is only about 15% of the aircraft that are flying at any given time. I guess by 2020 it becomes required and then the radar will be screaming. It's amazing to watch it grow and change!

SH

[DeeJay]

Not forgetting  KAC101 9K-AOA OKBK-EGLL, who today once more performed his favourite trick of seemingly flying sideways into LHR (Beats walking backwards to Christmas!), though when I saw him through my window he was pointing in the right direction. Compliments of the Season to you all (including all at San Diego)