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Follow up to last weeks mid air

chperplt

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It appears that the crew of the DHL plane followed their TCAS, while the Russian plane ignored the TCAS alert and followed the ATC request which in turn led to the collision.

What are you going to do in a similar situation? Do you trust your TCAS enough to disregard ATC?
 

Andy Neill

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First, I think the Russians got the TCAS alert to climb RIGHT before they got the Swiss instruction to descend. More on that later---

I've been following this because it feeds right into the first course I took in grad school which dealt with failures in the human-systems interface. Here is what I have derived:

Two aircraft were assigned altitudes that would put them on a collision course.

That’s OK because the air traffic control (ATC) facilities have automated alerts for such events to warn of impending conflicts.

But that feature was turned off for routine maintenance.

That’s OK because the control facility had a policy to always have two controllers present in such circumstances to provide another set of eyes.

But the other controller was not present because he was taking an unauthorized break.

That’s OK because there was still one controller there and the controllers in an adjacent sector (German) had the automatic alert feature on and working. They called the Swiss controller to point out the conflict.

But the German controllers were unable to get through because the Swiss controller was on the phone doing routine traffic coordination for another aircraft and was using the ONLY phone available.

That’s OK because the Russian aircraft had a traffic collision avoidance system (TCAS II) on board that would not only alert the crew to the danger but also give a suggested conflict resolution.

But the resolution given to the crew (to climb) was opposite the instructions given by the Swiss controller (to descend). The Russian crew delayed their response (perhaps as they sorted this conflict of instructions out in their minds?).

That’s OK because the German cargo plane also had TCAS II on board.

But the German plane’s TCAS II instructed the crew to descend (into the path of the Russian plane).
 

skydiverdriver

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Yup. This is just the problem I thought would happen with TCAS when it originally was mandated by Congress in the late 80's. Which one do you follow, ATC or the box? What if ATC doesn't know what either box is telling the pilots? Personally, I think this will become more common, especially if the US ever goes to non-government ATC. Scary thought.
 

flx757

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skydiverdriver said:
Yup. This is just the problem I thought would happen with TCAS when it originally was mandated by Congress in the late 80's. Which one do you follow, ATC or the box? What if ATC doesn't know what either box is telling the pilots?

The box. That's how we are trained. That's what ATC expects. What does it matter if ATC knows what either box is telling the pilots? Besides, ATC has no way of knowing what TCAS alerts pilots get unless or until they advise them. In this case, the 757 got a "descend" from its TCAS, the Tupolev got a "climb". Had both crews followed the TCAS, no "problem". It only became a problem when the Tupolev crew ignored the TCAS RA, and began its descent. BTW, the last transmission from the 757 crew was "TCAS Down", which is the proper ICAO R/T phraseology for an RA to descend.

True, this chain could have been broken long before this point, but when the Tupolev crew chose to ignore the TCAS RA, the last chance to break the chain was lost.
 
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skydiverdriver

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Yes,
I agree with you, follow the TCAS and tell ATC later. I was just talking about feelings I had about TCAS when it first came out 20 years ago. I think you took one sentence out of context. Thanks.
 

flx757

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Sorry. Thought you were posing a question. Just doin' my best to answer and to keep the conversation lively.;)
 

Dieterly

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"TCAS Down", which is the proper ICAO R/T phraseology for an RA to descend.
I thought the proper ICAO term was "TCAS DESCENT", but maybe I'm wrong.
 

GeorgeTG

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TCAS RA Mandatory

TCAS like GPWS are supplemental systems to ensure safety of flight.
Following a TCAS RA is mandatory.
Once TCAS is giving you a climb or descent, ATC is -by definition- out of thr loop.

Understanding your systems is the key to resolving issues of "who do you trust".

Even with proper training and all of our modern safety systems we still will not be able to eliminate accidents. but as you can see from Andy's thread the chain of events becomes longer and more convoluted.

Expect more TCAS training for the next couple of months...

P.S.: whatever happened to looking outside when you get a TCAS alert?
 
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