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In the mid-air collision over Uberlingen, why couldn't the DHL611 crew hear the instructions given by the controller to Bashkirian 2937 crew if both aircraft were on the same frequency?

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    $\begingroup$ Who says the DHL611 crew didn't hear? Are you making an assumption or do you have a source for that? $\endgroup$ – GdD Apr 18 '16 at 14:00
  • $\begingroup$ Hearing another aircraft being told to descend doesn't, in and of itself, give the crew enough to go on. The DHL crew followed the correct procedures by complying with the TCAS "Descend" command. $\endgroup$ – Ralph J Apr 18 '16 at 14:03
  • $\begingroup$ @GdD The DHL crew called out for TCAS-descent after the controller had twice asked the Bashkirian crew to expedite their descent. The second time he even relayed the position of the DHL to the Bashkirian(though it was incorrect). It was highly likely that it was the DHL aircraft that was referred to this situation. So, I inferred that the DHL crew didn't hear the ATC transmission. $\endgroup$ – Sreeram Apr 18 '16 at 14:32
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    $\begingroup$ Your inference is incorrect, according to the black box transcript the DHL crew did hear the transmissions. They did exactly as they were supposed to - ignored the radio and followed the TCAS instructions. $\endgroup$ – GdD Apr 18 '16 at 14:47
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    $\begingroup$ @Sreeram Here's the official report - it contains discussion of the DHL CVR and entirely agrees that the DHL pilots acted appropriately bfu-web.de/EN/Publications/Investigation%20Report/2002/… - see section 1.9.1 specifically $\endgroup$ – Jon Story Apr 18 '16 at 16:22
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It wouldn't matter if they had.

The DHL611 crew had been trained to obey TCAS orders over ATC. This was fairly common, but not universal practice at the time. Their training was unambiguous, and stated that TCAS should be followed over ATC instructions. They had been trained that both aircraft would follow TCAS and avoid the collision, and had no reason to believe that wasn't the case: they didn't even necessarily know that BTC2937 was the aircraft causing their TCAS alert

The crew of BTC2937 hadn't been trained to follow these priorities, or became confused.

From the Wikipedia page about the incident:

The TCAS Pilot's Guide was ambiguous as to whether or not TCAS advisories should take precedence over ATC instructions.[BFU 14] This ambiguity was replicated in the Tu-154 Flight Operations Manual, which contained contradictory sections. On the one hand, chapter 8.18.3.4 emphasized the role of the ATC and describes the TCAS as an "additional aid",[BFU 15] whilst chapter 8.18.3.2 forbids manoeuvers contrary to the TCAS

Since that accident, it was made official procedure for all flights to follow TCAS, ignoring ATC when a TCAS RA is in effect.

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    $\begingroup$ Although all you say is true, "it wouldn't matter if they had" doesn't answer the actual question. The question was not "would that have prevented the crash?" but "Why couldn't the DHL611 crew hear the ATC transmissions for the Bashkirian 2937 crew?". I don't know whether it's true that the flights couldn't hear the instructions for the other flight, but this is the claim, which should be handled by the answer - by either refuting the claim or by confirming it and giving reasons (for why the instructions were not audible for the respective other flight). $\endgroup$ – summerrain Jan 2 at 7:13

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