bsergonomics
Posts: 458
Joined: Thu Jan 31, 2002 5:07 am

Radar Range

Wed Nov 17, 2004 9:18 am

Quick Question (I hope):

At what range can a modern long-haul aircraft's radar reliably detect another aircraft? I appreciate that this depends on environmental factors and the size/RCS of the other aircraft; however, in normal circumstances (not best- or worst-case scenarios) at what range would you expect to pick up returns on another civil aircraft? For argument's sake, lets assume that that the other aircraft is a 30-seater ATP.

How much difference is there (if any) between the radar performance of a long-haul and short haul aircraft?

A more general/sanity check question:

Apart from the radar, transponder, the Mk 1 Eyeball and listening to radio traffic, are there any other techniques that you can use to detect/locate other civil aircraft?
The definition of a 'Pessimist': an Optimist with experience...
 
avt007
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RE: Radar Range

Wed Nov 17, 2004 9:36 am

The radar onboard aircraft is weather radar and as such is pretty much useless at picking up other aircraft. TCAS is your best bet, and I`m not sure what range that is capable of, although since it is line of sight, altitude will have a big part to play in the performance.
 
SATL382G
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RE: Radar Range

Wed Nov 17, 2004 9:37 am

I'm not aware of a commercial long haul jet that has a air search radar. Weather radar yes, but air search no. Are you refering to the TCAS & transponder?
"There’s nothing quite as exhilarating as being shot at and missed" --Winston Churchill
 
avt007
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RE: Radar Range

Wed Nov 17, 2004 10:15 am

Since TCAS is for avoiding collisions, long range isn`t any help. You don`t need or want to see traffic 50 miles away. The Bendix/King TCAS II in our F28s and Dash8s had a max display range of 15 miles.
 
QantasA332
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RE: Radar Range

Wed Nov 17, 2004 10:16 am

As mentioned above, TCAS doesn't employ radar. Rather, it operates using transponder transmitions. The original poster's question is still valid, however: at what distance can an aircraft pick up another aircraft on its TCAS (what is the range of its 'radar')? Transponders operate on the UHF band, so the question really boils down to "How far do UHF signals usually propagate"? Under normal conditions, most UHF transmitions have a range of around 100 miles. However, a number of tropospheric and general atmospheric conditions can sometimes exist which boost signal range by as much as 10 times.

So, an aircraft can detect another aircraft on its TCAS from about 100-1000+ miles away - assuming the other aircraft's transponder is operational!

Cheers,
QantasA332

Edit: I should add that while the above is the possible range, TCAS displays typically only show traffic when it is 15-20 miles away, as Avt007 pointed out.

[Edited 2004-11-17 02:18:35]
 
airplay
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RE: Radar Range

Wed Nov 17, 2004 10:38 am

I'm not aware of a commercial long haul jet that has a air search radar. Weather radar yes, but air search no. Are you refering to the TCAS & transponder?

Some GA/Business aircraft weather radar systems have a "target alert" function that detects small targets such as airplanes or ships on the ocean in ground map modes.

There is rarely enough resolution to actually paint the target on the screen, so these radars merely annunciate "TGT" or some similar label on the screen just to bring the pilot's attention to some target that the system detected.

The target detection function is usually limited to a small sector of the scan in front of the airplane. Typical maximum range is about 150 miles.

I don't recall seeing the target alert function on any radar systems installed in larger airliners.

lets assume that that the other aircraft is a 30-seater ATP.

I thought an ATP could carry about 70 people...


[Edited 2004-11-17 02:45:46]
 
air2gxs
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RE: Radar Range

Wed Nov 17, 2004 10:47 am

I do remember flying across the Pacific several times in a DC8 and were able to "see" other aircraft on the WX RADAR. No resolution, just a dot in the clear about 20 miles in front and then another 20 miles beyond. But then again those were the RDR1E RADARs. They could microwave an elephant if it stood in front of the antenna when it was radiating
 
PhilSquares
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RE: Radar Range

Wed Nov 17, 2004 11:31 am

In the days prior to TCAS, if you were really bored while in the NOPAC track you could always use the tilt to look for other aircraft ahead of you. It was good out to about 30 miles. The only display you had was a small oval shape. There was no air to air mode as such.
Fly fast, live slow
 
buckfifty
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RE: Radar Range

Wed Nov 17, 2004 12:03 pm

In the days prior to TCAS, if you were really bored while in the NOPAC track you could always use the tilt to look for other aircraft ahead of you. It was good out to about 30 miles. The only display you had was a small oval shape. There was no air to air mode as such.

I still do that on time to time. Paint the aircraft with the radar, see if it matches the TCAS display, then calculate the tilt range to see if I can match the altitude given by the TCAS. The latter obviously is an inexact science due to beam width, but whatever. Better than picking your nose between 160E and 170E.
 
Santhosh
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RE: Radar Range

Wed Nov 17, 2004 12:50 pm

What are the differences in functionality of Primary and Secondary radar installed in airports and its range of operation?

Thank you,
George
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bsergonomics
Posts: 458
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RE: Radar Range

Wed Nov 17, 2004 5:11 pm

To be perfectly honest, I'm slightly embarrassed about having asked the question. I guess I've been working with the military for too long...

To let you understand a bit more the reason for the question, I have been asked to look at concepts for applying military technology and techniques to civil aviation, one of the aspects of which is reducing separation distances in transoceanic and non-radar covered regions.

The key aspect is "See, Sense and Avoid" other traffic. The obvious question, therefore, is how best to do it, and what techniques can be used when one or more pieces of equipment fails?

To be honest, the ranges stated here for TCAS aren't really sufficient. The concepts that we're investigating need something that will highlight a potential problem long in advance so that an efficient solution can be found and applied long before there is any risk of collision.

We are aware that there are active research and development programmes for this type of prediction and resolution tools for ATC, but it relies on ground-based radar and instructions from ATC.

You also need to know that many of the current research programmes are aimed at achieving 'deregulated' airspace; i.e., removing the airways and specific altitudes in order to improve flight efficiency and increase capacity. This needs considerably improved See, Sense and Avoid equipment and techniques.

As such, thoughts or suggestions on how this might be achieved would be of great interest.

Many Thanks!
The definition of a 'Pessimist': an Optimist with experience...
 
FredT
Posts: 2166
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RE: Radar Range

Wed Nov 17, 2004 6:28 pm

Santhosh,
the primary radar emits radio energy and detects when the emitted energy has bounced off something and returns. It is akin to flashing a torch out into the night and measuring how much light returns from a given direction, timing the returns to get the distance.

A secondary radar sends an interrogation in a given direction. It is basically a coded radio emission, at much less power than what a primary radar would use. When this interrogation is received by the transponder in an aircraft, the transponder sends a reply. This reply is then received by the SSR (Secondary Surveillance Radar). Again, time is used to get the distance. The transponder code of the aircraft is included in the reply for identification. Mode C transponders also include the altitude in their reply. Then there are mode S transponders, which all have a unique ID. This means you can interrogate them much more selectively and also request more data from them if required. E g, TCAS II uses mode S to coordinate avoidance manoeuvres between aircraft.

Very briefly summed up, but I hope it was what you were looking for.  Smile

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
FredT
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RE: Radar Range

Wed Nov 17, 2004 6:36 pm

BSErgonomics,
Coupling ADS-B/VDL mode 4 and the FMS/INS should be the way forward IMO. Check out

http://www.nup.nu

or do a search for "Mediterranean Free Flight". Lots of work done on these. Just to tease you, I have a CD on it around somewhere that I really should find time to look at some day. Big grin

Optimizing flights for keeping the planned time to breakpoints, a standard deviation on the arrival times over a flight of around one hour ended up 7.3 seconds over thirty flights!

Putting the prediction capability of modern flight management systems in the hands of ATC and available to flight crews to manage their own separation could revolutionize the system.

Regards,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
airplay
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RE: Radar Range

Wed Nov 17, 2004 10:45 pm

To be honest, the ranges stated here for TCAS aren't really sufficient. The concepts that we're investigating need something that will highlight a potential problem long in advance so that an efficient solution can be found and applied long before there is any risk of collision.

Really? What sort of range do you consider sufficient to avoid risk of collision?
 
FredT
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Joined: Thu Feb 07, 2002 9:51 pm

RE: Radar Range

Wed Nov 17, 2004 11:16 pm

Airplay,
the demands which the air traffic system now has to live up to can't be solved through resolving conflicts as they happen. The main part has to be done already at the planning stage, making sure that the conflicts never happen. Ideally, your start-up at Heathrow will be delayed for a few so that a potential conflict on approach to Rome will be avoided. That has to be the target!

More realistically and in a shorter timeframe, we are probably looking at making sure we’re in the clear for enough time to plan around a conflict, as you would around a storm cell, rather than collision avoidance. This necessitates a warning time which is measured in minutes, at the very least.

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
bsergonomics
Posts: 458
Joined: Thu Jan 31, 2002 5:07 am

RE: Radar Range

Thu Nov 18, 2004 9:25 am

Fred,

Thanks for the input. I'm well aware of the Free Flight stuff - my boss was one of the key players in that.

Airplay, as Fred mentioned, we're not interested in collision avoidance. If we get to that stage, the rest of the system has already failed. We're interested in the ability to work out many (10-15, preferably) minutes in advance that one or both aircraft need to make a course or altitude change in order to avoid the conflict, and then work out the most efficient way of acheiving that deconfliction.

There is also the aspect of sharing information, such as wind velocity/direction at altitudes, based on the current experiences of other aircraft, so that the most efficient path can be taken by all aircraft within that sector. That's one of the fundamental things about the programme - it's not just about preventing the bad things happening; we also want to study and exploit the beneficial aspects as well.

Thanks for your thoughts, and keep them coming!
The definition of a 'Pessimist': an Optimist with experience...
 
SPREE34
Posts: 1563
Joined: Tue Jun 29, 2004 6:09 am

RE: Radar Range

Thu Nov 18, 2004 10:41 am

Santhosh,
To answer the "range" portion of your question, it varies with type of RADAR system. In the US, generally the ASR (airport) systems provide primary returns out to 60 nautical miles. The secondary (SSR or Beacon) may be used out to 200 nautical miles. The En Route systems (ARSR) are 200 nm, and 250 nm systems, with beacon systems to match. The newer ARSR4 sytems also provide elevation information, though it is only used by the military. Do a search on the terms " ASR or ARSR or add numbers behind them ie: ASR 12, ASR 11, ARSR 4, ARSS 12, and you will come up with many manufacturer's site to examine.
Happy surfing.
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