How can the contrller identify an aircraft with the mode s?

[ericliu]

Hi everybody:
Mode s is one of the identification method in radar control, but how exactly can a controller identify an aircraft with mode s? Could anybody tell me some details about that, such as the procedure to do that and the presentation on the radar screen.
Thanks a million!

[slatch]

Well it is very easy, if your control facility uses radar sites with Mode S interigators you will have a little more information. Most ATC facilities in the USA really have no Idea if your Mode S. Enroute centers to my knowledge have no Mode S inf avail. Some approach facilities with TIS get some Mode S information. Mainly Mode S in the US is used in the traffic systems that aircrat have installed. For more info......

Section 5. Surveillance Systems

Good Luck understanding it.....

[Minesapint]

The aircraft's identity is copied by the pilot into the FMS and downlinked by the aircraft. The airframe Mode S identification, 24 bit address, can also be used for identification purposes. PAN ATM section 8.

[Radarspod]

Minesapint - please say that no-one is actually planning to use 24 bit aircraft address for ID purposes! That is a disaster waiting to happen - it should only ever be used by technical systems.

RS

[Dan Dare]

I stand to be corrected, but isn't a bit a binary 1 or 0. Mode A has is a 12 bit system so it has 12 1s or 0s or 4096 (7777 in base 8 or FFF hexadecimal) codes. Mode S has 24 bits or 16777215 (77777777 in base 8 or FFFFFF hexadecimal). It is unlikely that anyone would input the binary code in to their Mode S transponder any more than anyone would input it in their Mode A transponder. Each aircraft has a 6 digit hexadecimal assigned to it as permanently as its registration (English aircraft seem to be in the form 40xxxx). If I interegate a return I can see the airframe permanent hexadecimal. The pilot can input the callsign via some interface that I don't really understand, but my display uses the Mode A Code Callsin Conversion Data to display the flightplan callsign.

Sadly I don't think any ATC system is yet sufficiently 21st century to allow identification purely based on the Mode S identity correlating with the expected flight.

[Jayfoe]

A few quick points;

1) The 24-bit address is purely used by the system to identify and selectively interrogate the aircraft. It is also used by the ACAS/TCAS system. The 24-bit address is unique to the aircraft and should not be used for operational purposes (ICAO Annex 10).

2) The aircraft ID can be set from the cockpit and should be either the ac registration or callsign. It is this data that is displayed on the radar screen, it isn't correlated from a database it is one of the parameters downlinked from the aircraft.

3) I believe that the current method of operation is to identify the ac using one of the current methods and then, after ensuring that the aircraft ID is correct, get the aircraft to squawk 1000 (mode 3A). However I stand to be corrected by someone who uses it.

4) In the future it should be commonplace to identify the ac from its downlinked ID and everyone will be flying around squawking 1000.

Jayfoe

[Lon More]

From Skynet, a bit more info about the system and its intoduction

[Someone_Else]

In the UK we don't use it as an identification tool, we use it for the parameters that are downloaded from the aircraft.

I don't know if there are any plans to allow Mode S as an identification method; certainly haven't heard anything about it.

(You may already know this, but if you don't read on)

Primarily Mode S (in the UK) it is used to display the pilots selected level and we see that on the radar at all times. Hence we know which aircraft have mode S and those that don't just by looking at the screen, a mode S equipped a/c would have a label that looks something like this:

ABC123
136 LL 150

The flight level after the intention code (coloured orange) is the selected level. This enables us to catch any errors and stop potential Level Busts. Furthermore we have tools that utilise the selected level to help us in congested airspace eg. Holding stacks.

There are some other parameters we get which help when controlling, those being IAS, GS, HDG & Vertical Speed.

[silverknapper]

Someone else

We fly around in old turboprops. We are Mode S equipped but it isn't linked to our altitude alerter. Before every flight we set the flight no in the transponder, are we wasting our time? Or rather if we forget it which sometimes happens have we annoyed anyone by flying around with the previous flight no set?

Cheers

SK

[Minesapint]

Minesapint - please say that no-one is actually planning to use 24 bit aircraft address for ID purposes! That is a disaster waiting to happen - it should only ever be used by technical systems.

RS

It can be used for the handover of flight - doc 4444 has it in there. NATS 'may' use it to support identification at system level - we will see.

[Minesapint]

Mode S aircraft identity will be used some day, maybe sooner than later. Keep on entering those flight details.

[Radarspod]

Primarily Mode S (in the UK) it is used to display the pilots selected level

Not quite right - Primarily in the UK Mode S is used to obtain surveillance data, such as a position measurement, Mode A code and Mode C altitude information - the DAPS such as Selected Altitude are a secondary function. All UK enroute centres are using Mode S derived surveillance data and have been for some time, with well over half the enroute radars now Mode S equipped.

Mode S is a protocol set used for datalink between a ground interrogator and an airborne transponder, not a set of tools at the centre. The new tools at the centres USE Mode S derived data (to display SFL for example), as do the existing display systems display Mode S derived Mode A and Mode C information.

Silverknapper -With regard setting the correct flight number at the transponder - the Mode S requirements for most countries if you are Mode S equipped require that the Aircraft ID is entered correctly for that flight. It is better that the aircraft operators get used to doing this now rather than waiting until ATC stop using Mode A codes and start using the entered flight ID. These are being monitored for correctness across Europe already, with some European countries looking to use it for Flight identification purposes very soon.

RS

[Minesapint]

Well said. The ID will be entered and validated by ATC on the ground in most cases. We don't want aircraft getting airborne into busy TMA airspace and not correlating now do we.

[ericliu]

Someone_Else：

ABC123
136 LL 150

The flight level after the intention code (coloured orange) is the selected level.

Does that mean you could see another flight level after 150? eg.
ABC123
136 LL 150 160 , 160 is the level selected by the pilot, and 150 is the level input by the controller. Is my understanding right?
Thanks a lot!

[ericliu]

Radarspod:

Primarily in the UK Mode S is used to obtain surveillance data, such as a position measurement, Mode A code and Mode C altitude information

I was confused that why you get Mode A code and Mode C altitude information from mode s? We can get these information without mode s. So what 's the relationship between mode A C and S?

[Jayfoe]

Ericliu

Mode S is completely backwards compatible with Mode 3 A/C, they use the same frequencies (1030 and 1090 Mhz). The current method of operation for most Mode S radars is to;

First;

All Call

Interrogate Mode 3 transponders for the Squawk, then;
Interrogate Mode 3 transponders for the Charlie Height, then;
Acquire the individual 24-bit address of Mode S transponders and lock them out.

Then;

Roll Call

Interrogate individual Mode S transponders using the 24-bit individual address. These interrogations will be of any information that the aircraft can downlink. (During the Roll Call period Mode 3A/C transponders will do nothing)

The Radar will then go back to another All Call period and start the process again. An aircraft should experience at least 4 All Call and 4 Roll Call periods per antenna rotation.

Mode S transponders will downlink their height and squawk during the "Roll Call" period and will ignore the initial Mode 3 Alpha/Charlie request in the "All Call" period.

[Radarspod]

close enough

ericliu - the confusion comes from terminology used to describe Mode A and Mode C.

Mode 3/A is a very simple interrogation/reply protocol used to obtain a 12 bit octal identity code, commonly known as Mode A code.

Mode C is also a very simple interrogation/reply protocol used to obtain a 12 bit octal pressure altitude code, which is converted by the interrogator to a Flight Level. Unfortunately, ATC also use the term Mode C to pressure altitude / flight level.

Mode S is a more complex but higher integrity set of protocols that can be used to obtain lots of different information, INCLUDING Mode A identity code and pressure altitude (Mode C to ATC). The data contained is the same as that extracted by the Mode A and Mode C protocols, it is just obtained a different way.

If you have a large population of Mode S transponders (we do in the UK) then there are benefits to extracting the Mode A and Pressure Altitude (call it Mode C if you must) from the aircraft using Mode S protocols rather than using Mode A and Mode C interrogations. Mode S implemented properly at both ends provides a high integrity data link with error checking, as well as the ability to address individual aircraft, saving on the use of 1090MHz.

As far as an ATC controller is concerned, when performing basic radar seperation function, whether the position, Mode A and altitude information has come from Mode S radar or Mode A/C only radar actually doesn't matter. It all looks the same. The confusion I mentioned above I believe comes with ATC calling altitude information "Mode C" when it hasn't been obtained using Mode C protocol, but via Mode S protocols. But Mode C is the traditional (and probably taught) terminolgy for pressure altitude and at the moment there isn't an alternative on the table, regardless of us using Mode S today.

What Mode S gives you is further data items that can be used to enhance the ability to provide that seperation function and in the future move away from the reliance on Mode A Idenity to the use of aircraft derived Callsign or Registration directly from the transponder Aircraft ID (BDS 2,0) register.

RS

[Jayfoe]

Hi RS,

Could you check your PM's?

Jayfoe

[Someone_Else]

RE: Ericliu

Does that mean you could see another flight level after 150? eg.
ABC123
136 LL 150 160 , 160 is the level selected by the pilot, and 150 is the level input by the controller. Is my understanding right?

No, the controller does not input any level. All we are seeing is what the pilot has selected, so just the one level displayed in orange.