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Joe Sharkey on Legacy Plane that hit Brazilian Airliner

Joe Sharkey on Legacy Plane that hit Brazilian Airliner

Old Jun 12, 07, 2:57 pm
  #226  
 
Join Date: Nov 2006
Posts: 35
Originally Posted by LarryJ View Post
That's not how it works. A XPDR/TCAS combo can and will stop working with the controls in the correct "on" positions. This is usually fixed by cycling the XPDR off then on again.
Thanks, but as I said in the first sentence of my last post, the Legacy cockpit voice recorder has it that the pilot said the TCAS was off or in stand by, implying that the transponder screen was displaying a "stand by" or "off" warning sign. That dialogue took place two minutes after the collision, when the pilots were trying to figure out what caused the big noise. Soon after that dialogue, the transponder was switched back on.
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Old Jun 12, 07, 4:19 pm
  #227  
 
Join Date: Nov 2006
Posts: 35
I just stumbled onto a very interesting NTSB document on the Gol-Legacy collision, from which I quote this passage:
Failures of the TCAS computer unit itself can also occur; however, these failures only affect the TCAS-equipped aircraft’s ability to detect nearby aircraft. The aircraft containing the inoperative TCAS unit remains visible to other aircraft as long as its transponder remains operative. The consequences of a TCAS unit failure are magnified, however, when the transponder is inoperative because not only is TCAS information lost on the affected aircraft, but also that aircraft will not be visible to other airborne collision avoidance system.
And here is another passage, just as interesting:
About 2 minutes after impact (at 1959:13.5), the first officer questioned whether TCAS was on, the captain confirmed it was not and, immediately afterwards, the transponder signal returned to ATC radar returns. Therefore, there is evidence that the flight display warning was available to the crew but not noticed and acted upon until after impact.
Wiken is offline  

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