Alien Shores,

A not to in depth discussion on the operation of transponders can be found on this AvWeb Transponder Basics link

A total of 4096 transponder codes are available under the present arrangement of 0-7, these are decimal numbers that are just converted to binary (ie 0 is converted to 000, 7 is converted to 111) so the pulses that are sent back to the ATC radar antenna at 1090 MHz in 20.3 microsecond blocks contain these transponder code binary pulses and the encoded altitude which is also a binary number encoded into a bunch of 0's and 1's.

:rolleyes:

While speaking of Mode S.
Anyone having the status regarding Eurocontrol (ICAO ?) introduction of Elementary and later Enhanced Surveillance functions to the Mode S ? Ref the addition of DAPs (Down Link Aircraft Parameters).

I’m not fully updated on this, but my understanding is Elementary Surveillance includes, among other things, the requirement of the Mode S to automatic report aircraft identification.

stab trim

Try here for info from the horses mouth.

Eurocontrol Mode S Information

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10 West
UK ATC'er
[email protected]

[This message has been edited by 10W (edited 18 May 2001).]

Thank you 10W. Very informative site.

I think a computer nerd might argue that a squawk code is not a decimal number, it is an octal (base 8) number.

The reason for it (as Zeke points out)is that octal numbers convert exactly to binary, whereas decimal numbers do not.

8^4=4096
2^12=4096

You've wandered a bit off the thread here but just to answer 411A's comment that not all TCAS equipped aircraft have mode 'S' transponders.

TCAS equipped aircraft have mode "S" Transponders, that's how TCAS works. The TCAS creates a 'protected area' around the aircraft by interrogating nearby transponders operating in modes A, C or S. The TCAS antennae are direction sensitive but are accurate to only about 10 degrees or so. In combination with the range data obtained from the transponder replies the TCAS Processor derives a closure rate, and determines the threat level. If the TCAS determines that a threat exists, it tries contacting the target aircraft via the mode 'S' transponder data link. If the target is also TCAS equipped the two TCAS cooperate via mode 'S' to calculate a joint avoidance manouvre with one TCAS advising a climb or hold and the other a descend or hold manouvre. If the target aircraft has only mode A/C then a cooperative response is not possible and TCAS assumes that the target aircraft will continue its present flight path. TCAS then computes an avoidance manouvre based on no cooperation from the target.

To emphasise. By definition, ALL aircraft that have TCAS have mode 'S' transponders.

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Through difficulties to the cinema

Blacksheep---
You may be interested in knowing that our company aircraft (Lockheed 1329) has a mode "C" transponder fitted and also has TCAS I. Your statement about mode "S" transponder requirements is correct regarding TCAS II.

Blacksheep,

I have to concur with 411A, for TCAS I you do not need a transponder at all, only the threat aircraft does, the TCAS I system can have its own transmitter/receiver independent of the transponder.

TCAS I will happily work even if the threat aircraft only has a Mode A transponder. TCAS I provides a flight deck display of traffic in the vicinity and, if appropriate, alerts the pilot that an aircraft presents a potential threat by generating a Traffic Advisory (TA).

TCAS II will provide TAs and, if the system calculates a risk of collision with an intruder aircraft, which is equipped with an altitude reporting transponder or TCAS, recommend avoidance maneuvers, in the vertical plane, to the pilot by generating a Resolution Advisory (RA). TCAS II you can still get an RA if the threat aircraft only has Mode C (for the altitude encoding). For a co-ordinated RA, both aircraft need Mode S for the inter aircraft data link.

TCAS II equipped aircraft use the Mode S transponder connected to the top and bottom antennas to do the transmitting and receiving.

:rolleyes:

I stand corrected. You are right about TCAS I.

But TCAS I? That should have gone out with the ark. Even TCAS II with v7.0 software is only a short term interim solution to the full intent of European ACAS requirements. In US airspace TCAS II with v7.0 software is the current standard for heavy public transport machines. It ought to be standard for all aircraft everywhere but of course, safety has a price that politicians are not willing to pay. Cheap travel for the masses is far more important. :rolleyes:

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Through difficulties to the cinema

Blacksheep,

As I said on the previous page to this thread, TCAS I is mandated for use by a number of regulatory authorities for turbine-powered, passenger- carrying aircraft having more than 10 and less than 31 seats. i.e. turbopros of the Jetstream 31/32, B1900, Metro size.

:rolleyes: