Narrative:

ATC gave us a descent clearance from our cruise altitude of FL360 to FL340. The copilot started the descent using the vertical speed mode of the autopilot. I was the pilot not flying. As the aircraft passed through FL350; we received a TCAS traffic alert. Because the copilot had selected a high rate of descent on the vertical speed selector; our traffic alert quickly change to a TCAS resolution advisory (RA); telling us to 'monitor vertical speed.' at that time; the copilot turned off the autopilot and responded to the RA. We were still in a steep descent. Events were starting to take place rapidly. ATC called us and told us of traffic below at FL330. He must have asked what we were doing and I told him we were responding to a TCAS RA. He questioned my response and again I told him that we were responding to a RA. I responded to the ATC call while monitoring the copilot's actions. This is where we probably descended through our clearance altitude of FL340. When I looked at the TCAS information on the vertical speed indicator; it seemed to me the copilot was not reacting properly for the information displayed. The green arc was a band about 500 FPM wide starting at about minus 2;000 FPM and ending at about 2;500 FPM. The red arc started at minus 2;500 FPM and went below that. I told the copilot he had to reduce his descent rate; but he believed he needed to increase his rate of descent; that made me hesitate and rethink my interpretation of the display. I again told him we needed to stop descending. I believe the aircraft was descending 3;000 FPM or more. The copilot still believed he needed to continue this descent. I told the copilot I had the aircraft while I grabbed the control yoke and pulled up. This action stopped the aircraft's descent and started a shallow climb. I remember seeing a solid red colored traffic symbol with a -300 next to it. The traffic passed under us and slightly to our right. For a two thousand foot descent; the copilot selected a high rate when first descending out of FL360 for the altitude loss required (2;000 ft). That probably is what triggered the TCAS alert. I should have taken over aircraft control earlier. My decision was delayed because of my expectation that my experienced copilot would respond correctly to the TCAS display; that made me hesitate and question my correct interpretation. That cost valuable time and critical loss of altitude. Also the calls from ATC distracted me and delayed my processing of the situation.

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Original NASA ASRS Text

Title: A B737 First Officer responded incorrectly to a TCAS RA after he increased the aircraft's rate of descent when the resolution was to decrease the descent rate.

Narrative: ATC gave us a descent clearance from our cruise altitude of FL360 to FL340. The Copilot started the descent using the Vertical Speed mode of the autopilot. I was the pilot not flying. As the aircraft passed through FL350; we received a TCAS Traffic Alert. Because the Copilot had selected a high rate of descent on the Vertical Speed selector; our traffic alert quickly change to a TCAS Resolution Advisory (RA); telling us to 'Monitor Vertical Speed.' At that time; the Copilot turned off the autopilot and responded to the RA. We were still in a steep descent. Events were starting to take place rapidly. ATC called us and told us of traffic below at FL330. He must have asked what we were doing and I told him we were responding to a TCAS RA. He questioned my response and again I told him that we were responding to a RA. I responded to the ATC call while monitoring the Copilot's actions. This is where we probably descended through our clearance altitude of FL340. When I looked at the TCAS information on the Vertical Speed indicator; it seemed to me the Copilot was not reacting properly for the information displayed. The green arc was a band about 500 FPM wide starting at about minus 2;000 FPM and ending at about 2;500 FPM. The red arc started at minus 2;500 FPM and went below that. I told the Copilot he had to reduce his descent rate; but he believed he needed to increase his rate of descent; that made me hesitate and rethink my interpretation of the display. I again told him we needed to stop descending. I believe the aircraft was descending 3;000 FPM or more. The Copilot still believed he needed to continue this descent. I told the Copilot I had the aircraft while I grabbed the control yoke and pulled up. This action stopped the aircraft's descent and started a shallow climb. I remember seeing a solid red colored traffic symbol with a -300 next to it. The traffic passed under us and slightly to our right. For a two thousand foot descent; the Copilot selected a high rate when first descending out of FL360 for the altitude loss required (2;000 FT). That probably is what triggered the TCAS Alert. I should have taken over aircraft control earlier. My decision was delayed because of my expectation that my experienced Copilot would respond correctly to the TCAS display; that made me hesitate and question my correct interpretation. That cost valuable time and critical loss of altitude. Also the calls from ATC distracted me and delayed my processing of the situation.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.