B737-300
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 200
Training / Qualification; Time Pressure; Human-Machine Interface; Confusion; Communication Breakdown; Situational Awareness
Conflict NMAC; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued Advisory / Alert; Flight Crew Took Evasive Action; Flight Crew Became Reoriented
Human Factors
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.
I was the First Officer and pilot flying. We were at FL360 and given a clearance to descend to FL340. I went to the Descent page and executed Descend Now. The aircraft started a 1;000 FPM descent until approximately FL355 when it reached the descent path and pitched over to a 3;000 FPM descent. An RA was triggered approximately three seconds later; saying; 'Monitor Vertical Speed.' I immediately kicked off the autopilot and referenced the TCAS. There was a huge red band from approximately -700 FPM to -4000 FPM. There was a very small green band from about 500 FPM to 700 FPM. I mistakenly read the TCAS and initially increased the descent. I tried to tell the Captain to notify ATC of our RA and that we would be descending below FL340. He was trying to tell me to level off; but I was trying to tell him I was trying to comply with the RA. We were talking over one another with little or no time to spare to fix the problem. He started to pull back on the yoke about the time I realized that I needed to shallow the descent. We leveled off at FL334; 600 FT below our assigned altitude.After the event; I heard ATC asking if we had heard him calling out the traffic at FL330. I never heard the call. I learned after the event that they had called after the RA had gone off. At that point; I was fully trying to comply with the RA and tuning the radio out so I didn't hear the traffic call. By the [time the] Captain answered the traffic call; precious seconds were lost instead of him trying to correct my mistake. Another threat was this event happened VERY fast. At the descent rate we were at and the short descent; there was no room to make the error I did. A lot of time we get the luxury of time to catch our error and rectify it. Not in this case. Another threat was being startled. It is a fairly low work environment in the mid FL300s and an RA at that altitude gets your attention. I was startled and it took a few seconds to realize what was happening. I happened to misinterpret what I saw. Another threat was the TCAS instrument itself. In the -300 it is a round dial. When the RA occurred; we were at -3;000 FPM; which is about the four to five o'clock position on the dial. It was all red until about the eight o'clock position. It was not immediately apparent to me that the TCAS wanted me to shallow the descent looking at the instrumentation. I think in the heat of the moment I looked down and swapped the dial from the left being zero to the right being zero and felt the urge to push through the red to the green on the left. I recommend that all TCAS instruments in the future be vertical so pilots; in the heat of the moment; would see clearer pictures of what to do. Another threat is the lack of communication of the threatening aircraft prior to the event. In most of my other RA events; I could see a situation developing. In this case; I was startled and made a wrong decision.
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.