Mode S Transponder

[TechMan]

For those folk that have mode S transponders, be advised that RA-Aus has been allocated 5000 Mode S codes by the CASA.

 

Therefore, if you want to put a mode S in and need a code, let me know at the office and I will allocate you a code.

 

Chris

 

 

[Dieselten]

What is the theoretical maximum number of codes that can exist? At the moment the CASA register has 12845 registered aircraft on it but I assume not all will require Mode S codes because many will already have them anyway if they are Mode S equipped. Ultimately I also assume every CASA-registered a/c will need a discrete Mode S code.

 

5000 RA-Aus codes...will this be enough for future growth in ultralight and RA-Aus regsistered LSA types? Also, I assume this would leave enough for the HGFA to issue for their weightshift microlights and any other HGFA-registered aircraft that may require Mode S in the forseeable future?

 

Can aircraft in different countries have identical codes? (I am assuming the maximum number of codes is in the millions so the problem of actually running out of codes is purely academic.)

 

 

[Guest browng]

At the moment the CASA register has 12845 registered aircraft on it but I assume not all will require Mode S codes because many will already have them anyway if they are Mode S equipped.

Every aircraft added to the CASA register is allocated a code at that time, even if not transponder equipped. My 1946 J3 has one on the registration certificate, and it does not even have an electrical system, let alone a transponder.

 

 

[WestCoast]

I jumped the gun somewhat and had a Mode S transponder fitted to my aircraft by the factory prior to delivery in May 2006. Not a good move really as I expect that Air Services will be providing a subsidy for ADS-B equipment when it is implemented.

 

I also had the address module programmed but none of the radar services in Australia can see it as yet.........here is a recently received response from AirServices.

 

"Airservices Australia has ordered new Mode S radars for the major terminal areas, and they’ll be commissioned over the next few years. The first of the new radars to be commissioned will be in Sydney – I understand commissioning will take place next year.

 

The current terminal and enroute radars around Perth are not Mode S radars (they’re over 15 years old). Perth controllers will only see Mode A/C returns from your transponder until the new radar is commissioned and the ATC automation system is updated for Mode S."

 

 

[John Brandon]

What is the theoretical maximum number of codes that can exist? At the moment the CASA register has 12845 registered aircraft on it but I assume not all will require Mode S codes because many will already have them anyway if they are Mode S equipped. Ultimately I also assume every CASA-registered a/c will need a discrete Mode S code.5000 RA-Aus codes...will this be enough for future growth in ultralight and RA-Aus regsistered LSA types? Also, I assume this would leave enough for the HGFA to issue for their weightshift microlights and any other HGFA-registered aircraft that may require Mode S in the forseeable future?

 

Can aircraft in different countries have identical codes? (I am assuming the maximum number of codes is in the millions so the problem of actually running out of codes is purely academic.)

Mode S allows 24 bits for the unique ID so 16.8 million. Here's a little more about Mode S, for more see www.raa.asn.au/comms/safety.html#transponder

6.3 Aircraft radar beacon transponders

 

Transponders are specialised radio devices forming the airborne part of the Air Traffic Control Radar Beacon System [ATCRBS or "at-crabs"]. Transponders respond to a 1030 MHz interrogation pulse, from an Air Traffic Control secondary surveillance radar [sSR], by returning a high energy 1090 MHz pulse which strengthens the radar return signal. (Primary radar surveillance exists only within about 50 nm of the major civilian and military airports but such radars don't interrogate airborne transponders, SSR range is at least 100 nm from the radar unit.)

 

In addition the response from transponders fitted to smaller civilian aircraft normally consists of a 12 bit identity/status code plus a 12 bit altitude reading [in units of 100 feet] which appear on the controller's SSR screen with the aircraft 'paint'. Civilian units with this identity [Mode A] plus altitude encoding [Mode C] interrogation response capability are known as Mode 3 A/C [or just Mode A/C] transponders.

 

The transponder receives the Mode C altitude data from an altitude encoding altimeter or from a blind encoder; the latter probably being an electronic device with a pressure transducer connected to the static vent feed. Both types of units send pressure altitude not altimeter indicated altitude. (Some encoders are also capable of supplying altitude data to a GPS – "baro-aiding".)

 

The 12 bit identity code is separated into four 3-bit numerals using octal rather than decimal notation, thus each numeral will be in the range 0 – 7, i.e. the numerals 8 and 9 will not appear in any identity/status code. The standard four digit identity code 'squawked' by VFR aircraft is '1200' until radio contact with Air Traffic Services, who might then instruct the pilot to squawk an assigned individual code e.g. 4367 – the maximum number of pilot-selected identity codes available for assignment at any one time is only 4096.

 

The Mode A/C surveillance system is very limited. The transponders carried by regular passenger transport aircraft use a 24 bit identity code allowing a total of 16.8 million individual addresses. Thus every aircraft can be permanently assigned a unique address, usually based on the aircraft's country of registration and registration number. Consequently those aircraft can be selectively addressed by ground stations or other aircraft. This message format is called Mode S [for 'selective address'] but the transponders also have the normal Mode A/C functions.

 

Currently in Australia the main Mode S transponder function is to allow aircraft equipped with Traffic Alert and Collision Avoidance Systems to 'talk' directly with each other thereby enabling mutual resolution of potential traffic conflicts; see below. Such transponders also act as the aircraft's digital modem terminal for data upload/download and distribution. Mode S can also provide faster more accurate ATC surveillance provided the ground radars are of the fast single pulse interrogation type. Many [most?] of the Australian SSRs are not monopulse radars and thus need to be replaced; this expensive requirement is prompting an accelerated implementation of ADS-B instead of new radars.

 

John Brandon

 

 

[Ausmo]

For those folk that have mode S transponders, be advised that RA-Aus has been allocated 5000 Mode S codes by the CASA.Therefore, if you want to put a mode S in and need a code, let me know at the office and I will allocate you a code.

Chris

Chris, now I am confused (not uncommon). I emailed Dean Tomkins for a code and he referred me to CASA....................................help!

 

Erik

 

 

[greybeard]

errr, check the date of the post you've replied to. Things may have changed in the last 4 1/2 years ;)

 

 

[Ausmo]

errr, check the date of the post you've replied to. Things may have changed in the last 4 1/2 years ;)

Whoops, you are no doubt correct!

 

 

[Yenn]

Why would ypu want mode S in an RAAus reg plane. You don't need it in a GA plane unless you go into class A airspace