ATC and TCAS ????

[ATC Watcher]

Shore Guy :

Very good paper you wrote for your crews, small factual errors but the message getting out is the good one.
One error however I cannot let pass is your reference to the internet rumour about the Lufthansa refusing the clearance to take off on account of his TCAS … total bull..
There was no Lufhansa on the sequence in Linate at that time, the aircraft that was lined up and wait after the SAS took off was I-LUBI and after the TWR called the SAS 5 times (unsuccessfully ) , they ordered the I-BI to vacate the runway via R1 back to the apron. ( If you want to be sure, check Appendix P of the report , the transcript of the TWR freq. )

My dear Skyhawk

Sorry about your friend. Really.
Did he die in vein ?
No because , much more people are now aware of the interface ATC-ACAS problem . ICAO wrote additional text in November 2002 that has found its way this time in training manuals.
Will it never happen again then ? That is far from certain. There are still may traps in the TCAS logic and grey zones in the human interface.
The line is still, ATC stop to be responsible as soon as pilot report a n RA. If a pilot follows an RA but does not report it, controller may ( and will ) interfere. So Ueberlingen could happen again .

In our case here the TU154 crew did not report they were receiving an RA and the B757 crew did so 23 seconds after starting to manoeuvre ( a very, very long delay for ATC and especially in that case ).

The controller issued the clearance to the TU154 to descend prior the RA were started, and did not issue any different instructions after the RAs started.

Standard ATC – TCAS interface would you say.

So why a collision then ?

First , to all of you out there with an ATPL :
Consider the human factors aspects of the following :

The airline you fly for has all manuals ( translated ) in Russian . always had, (an ICAO language even ).
Your national AIP sates that a pilot must always follow an ATC instruction unless in emergency . ( like in many other AIPs as this is an ICAO recommendation )
ACAS RAs are not defined as emergency and the word RA ( Resolution Advisory ) is translated in verbatim : an advisory, not a command.
Then you fly at night, your are under supervision and your instructor is sitting besides you on the right seat. You FO is in the jump seat behind you. You set your TCAS display on max range and spot, well before the TA , an aircraft at same altitude .( you say : “ he is showing us zero “)
When the TA starts, it confirm what you saw all the time and you are not surprised.
When you later receive a clearance by ATC to descend , you are not surprised and comply
Your instructor even tells you : “ descend ! “ .
When an RA starts, you are surprised , your FO tells you : “it says “ climb “ but you are already descending. Your instructor is telling you : “ He is guiding us down “ but before you are finished thinking the controller repeat his clearance to descend, since you forgot to acknowledge the first clearance.
You continue to descend.
You still see the traffic ( despite the wrong indication by the controller of 2 o,clock instead of 10 ) and say : “here on the left ….” Then things go wrong , the 757 grow bigger and bigger of course you try to avoid visually, you dive further and turn, and deviate from both TCAS RA and ATC clearance , and you hit with your left wing the vertical stab of the 757. , missing it by about 2 meters…..

Now my friends, tell me how you think you will have reacted at that time if you were the TU154 captain flying that night ?
No benefit of hindsight, no new procedures, with what you knew about TCAS in July 2002 ?

From an ATC point of view, the situation in which the controller found himself that night is a total management failure. Alone with degraded radar system, main telephone out of service, wrongly programmed back up telephone, unscheduled inbound to a normally closed airfield at night forcing him to open a separate position with a different frequency , leaving him 2 frequencies and 2 radar pictures to monitor on 2 positions several meters apart. Short tem conflict alert disabled, etc…
He spotted the conflict late, issued an expedite descend clearance to the TU154 ( as it was anyway coordinated lower with adjacent centre) and when he saw the Mode C of the TU154 winding down , he considered the problem solved. What he did not know is that the 757 had already started his descent as the radar return rate on that degraded mode was very slow. The 757 FO was PNF ( doing the R/T) and had left the cockpit leaving the Capt alone at the time of the RA, so he did not warn ATC immediately. When F/O came back 23 seconds later, he informed ATC using a wrong call sign, but irrelevant since the transmission was blocked by the A320 inbound to FH on the other frequency. ( the controller had admitted he did not hear the 757 call ).
There you go.
Without knowing that any of the aircraft was following an RA , the ATC clearance issued was a solution that should have solved the conflict in the mind of the controller.
But even If both pilots had reported they were following an RA, the controller would have said nothing as ATC is supposed to stop issuing instructions ( and be responsible for anti collision )after that point .
Without ATC , no collision. without TCAS no collision, if they would have been IMC , probably no collision.
Small things , errors, or small deviations from procedures, insignificant if taken in isolation ,are causing a tragedy when put in a certain sequence. Mixing automated systems with humans decisions is not and never will be a good choice.

Are we so sure this will never happen again ? I doubt it.

TCAS is far from being perfect and will contribute mathematically to more collisions . ( I remember hearing from the MITRE corp in the US , the owners of the sofware, something like for every 30 collisions it saves , TCAS will cause one ) But each collision will highlight more problem areas and more people will learn from them and try to avoid them in the future.

For this your friend probably did not die for nothing .

A last wish :
If I had some power I would mandate the following :

ALWAYS FOLLOW THE RA and never ever manoeuvre against it ! is the sticker that should be printed and put above every TCAS display .