I decided to start this thread as a follow up of the “ Ueberlingen trial “ thread which was used by some to re-open what I call the “ TCAS Philosophies “
If a mod would like to move the posts in the Ueberlingen trial thread here, welcome, but not necessary.
The TCAS system is very complex, there is no more than a dozen persons in Europe and in the USA who fully grasp everything, and no more than a few more dozens that understand more than 50% of it . ( I classify myself in the second category )
What is below is not a lecture, this is basic stuff to help you understand where we are .
A few facts :
The Ueberlingen collision revealed to the public ( but not to the specialists) a few flaws in its logic , mainly that the RA sense reversal did not work. (That is when one aircraft follow the RA , but the second maneuvers in the opposite direction of its RAs and both aircraft end up towards each other ).
There was request made from Eurocontrol to re-open the work on TCAS and make a software change to correct this flaw, but the FAA refused initially as version 7 was “ final” in their eyes and that the TCAS Team had been disbanded. Nevertheless though RTCA , discussion were restarted and what became known as Change Proposal 112 ( or CP112 ) became a fact, later it became 112E ( enhanced) , and , since we were re-opening the Pandora box, we added a few more flaws corrections mainly one ( CP115) on the replacement of the RA ‘ Adjust vertical Speed ,Adjust “ to :” Level off , Level off “ and another one (CP116) on weakening RAs at low altitudes .
There is a chance now that we will get a new version 7.1 in the” future” . I do not put “ near future ” as the date is still fought between Eurocontrol which would like 2010 for all, and the FAA which says “ much later” for CP 112E ( sense reversal ) and is against CP 115 , the “Adjust/ level off “ change .
In case you are lost in the TCAS / ACAS versions here is a short recap :
TCAS is a brand name. ICAO call its Specs ACAS
2 current sofware versions of TCAS flying around : 7 and 6.04 A
Udate to 6.04A was free, 7 was not . 7 was pushed by the Europeans, FAA was against it. 7 is RVSM compliant , 6.04A is not.
If a new version comes ( 7.1 ) , will it be mandated ( i.e free) or will it be recommended ( at a cost ) is a good question to which I do not have the answer.
Initially there were 3 TCAS intended , TCAS I : TAs only , TCAS II RAS in vertical plane, TCAS III RAS in both vertical and horizontal plane. Work on TCAS III stopped as the logic proved too complex, and vertical plane RAs were more effective at avoiding a collision. So there will most probably never be any TCAS III .
This is the situation today .
Now questions asked were : is a new Ueberlingen possible today :
With TCAS sense reversal logic flaws : yes , nothing has changed since 2002. same logic. Same version flying around (7.0).
With procedures : maybe : ICAO has revised its documentation and most training material have highlighted the way to follow in case contradiction between ATC clearance and RA. But incident statistics so far both from USA and Eurocontrol show that some controllers still issue clearances contrary to RAs and that pilots still choose to follow ATC instead of RA.
( a recent case in France, with US trained and experienced 767 pilots from a major US airline , so no need to think it only affect exotic or Russian pilots )
Main reason : lack of understanding on how humans and automated machines function in reality. Prof Ladkin in his excellent paper
http://www.rvs.uni-bielefeld.de/publ...rts/SCSS04.pdfon causal analysis after Ueberlingen call this “ Sociotechnical systems “ .
Now a last statistic : ( coming from Bill Thedford, of the Boston MIT LLC, one of the top 12 in my first classification earlier) Ueberlingen type encounters ( sense reversal ) occurs at 4.7 x 10 to the minus 6 per flying hour , or 58 events a year in Europe .If we expand this model, Bill predict that we could have 1 Ueberlingen –type mid air collision every 4 years due to the logic flaws.
The conclusion of this all :
Do not philosophy about TCAS : It is too complex a system. My advice : if you are a pilot : follow the RA, and if you are a controller and you have to give anti collision instructions , give a turn as well, in case TCAS comes in , it will complement your instruction instead of nullify it.
If you found this too long , this was the ( very) short version.
Safe flying.