TCAS Algorithms

[Smurfjet]

Greetings,

I'm looking for mathematical formulas used to calculate TAU and CPA in the TCAS algorithms, you can PM me if you wish.

Thanks

[FunctionedSatis]

I think you'll be very lucky to find this information in the public domain.

The algorithms are probably proprietory data held by Honeywell.

Stu

[PPRuNe Radar]

The TCAS algorithms are part of the spec designed by RTCA (Radio Technical Commision for Aeronautics) Inc for the aviation community. They are a non profit organisation that includes roughly 250 government, industry and academic organisations from the United States and around the world. Together they work on CNS/ATM issues and standards.

You can buy the TCAS specifications and algorithms by looking up the appropriate document and then sending lots of money to them ;)

http://www.rtca.org/downloads/doclist.htm#_Toc79999068

DO-185A is the document you probably want (for TCAS II).

DO-185A, Minimum Operational Performance Standards for Traffic Alert and Collision Avoidance System II (TCAS II) Airborne Equipment

Issued 12-16-97 s Prepared by SC-147

This document provides Version Downloadable 7.0 of the TCAS II logic and sets forth the minimum operational perfor_mance standards for TCAS II equipment. Among the changes, this Version Downloadable improves the system's surveillance performance and modifies the interference limiting algorithms to account for aircraft densities near airports as well as to permit longer range surveillance. Improvements have been made in tracking Mode S targets and in permitting TCAS to receive the extended Mode S squitter. To preclude repeatedly issuing Traffic Advisories (TA) against the same target, changes have been made to ensure that a target's TA status is maintained in slow closure situations by using more stringent drop criteria. Other changes include credibility checks to ensure integrity of the data being supplied to the collision avoidance logic and additional, more thorough tests for installed equipment.

Volume I contains the rationale for equipment characteristics, minimum performance standards, bench test proce_dures, and installed equipment performance.

Volume II presents the required collision avoidance algorithms in a state chart formulation with informational commentary text.

Attachment A provides both high and low level pseudocode representations of the collision avoidance algorithms. The standards and performance requirements in the document ensure that TCAS II is fully interoperable with other elements and equipment of the National Airspace System.


Note:

TSO-C119b -Requests for a Copy of the CD-ROM Titled “TSO C119B Changes to DO-185A, Approved by

SC-147 RWG* dated December 4, 1998 should be directed to: Federal Aviation Administration, Headquarters, Technical Programs & Continued Airworthiness Branch (AIR-120), (P) 202-267-9578.


Available in CD Format ONLY

List Price

US/Canada/Mexico $315.00

All other countries $405.00

Member Price

US/Canada/Mexico $126.00

All other countries $162.00

[FunctionedSatis]

now there you are, learn somthing new everyday!:ok:

[End_of_Descent]

Smurfjet,

there are some references available in the public domain.

Good introductory reading is this FAA booklet on TCAS II V7.0 : http://www.smartcockpit.com/operations/TCAS.pdf . It has nice background knowledge but few mathematical details.

More details can be found in the PhD Thesis by Dr. Raoul R. Schild which is available online at http://www.eos.tuwien.ac.at/Oeko/RSchild/Rules/index.htm . The appendix A1.4 (http://www.eos.tuwien.ac.at/Oeko/RSchild/Rules/id235.htm) has some mathematical details. However, they have been copied over - apparently - from the PhD thesis of Dr. Harro von Viebahn at Darmstadt University. The presentation in v. Viebahn's thesis is much (!) better and more clear, being an excellent reference on the mathematics of TCAS.

v. Viebahns Thesis is - however - only available in paper but not online and written in German. The full reference is
as follows:

v. Viebahn H., "Konzeption und Untersuchung eines boardautonomen Systems zur Vermeidung von Kollisionen im Luftverkehr", PhD-thesis, Technical University Darmstadt, 1997

Last but not least you might want to look into Nancy G. Leveson's "Sample TCAS Intent Specification" (http://www.safeware-eng.com/publications/TCASInt.pdf). This book however is *very* technical and hard to read. You'll have a hard time extracting useful information from it if you are not familiar with the topic.

Sure, all these references do not include any propietary material by Honeywell and information on the latest filters used for special cases used in the latest TCAS software versions.

If you can read German, get v. Viebahn's thesis which is a great reference on the basic mathematical models and their limitations with all the derivations from basic formulae.

EoD

[Smurfjet]

You've been very helpful. Thank you very much :ok: