B737-700
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 151
Situational Awareness
Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Became Reoriented; Flight Crew FLC complied w / Automation / Advisory
Human Factors
Descending on the DIRTY3 Arrival at FL330 in moderate precipitation; visibility zero in clouds; night IMC; we experienced moderate chop to light turbulence. Crew discussed and requested a descent below turbulence. ATC cleared us to descend to FL290. We had turbulence throughout descent. Highest level of automation selected. VNAV SPEED descended aircraft at 2;500-3;000 FPM.I was looking at my EFB to verify proper approach was loaded in FMC and to review approach and taxi diagrams. Was having trouble reading the charts due to turbulence and lighting. At approximately FL315 we received a TCAS alert; 'traffic; monitor vertical speed.' Almost immediately followed by 'adjust vertical speed; adjust.' This caused me to look again at the automation and altitude set in MCP. Based upon our descent rate which was quite high I elected to disconnect the autopilot and autothrottles in order to comply with the alert. The aircraft was trimmed with high nose down pressure at the time of disconnect.At this time my First Officer informed me that there was traffic below us and we should probably climb. By the time I could get my bearings due to the turbulence and weather conditions (we estimated about three seconds) we then received a TCAS RA 'Climb' alert. The turbulence and weather conditions at the time of event certainly caused a distraction and brief second or two of confusion as I transitioned to the PFD guidance.I added power and reversed direction to initiate a climb. I believe we were just above FL290 when the climb was initiated. I climbed to about 30;600 feet MSL. At about FL300 I recall hearing 'clear of conflict.' I also heard (another carrier) aircraft on the arrival report to ATC that they had received a RA climb alert as well. We reported to ATC that we also had a RA climb and were leveling off. ATC advised that there was (another carrier) aircraft at FL280 and cleared us to descend back down to FL290.I alerted company Dispatch via ACARS and also called them upon landing to see if they needed more information.In hindsight after verifying that the automation was correctly set; I might have done better to first attempt responding to the TCAS alert by transitioning to MCP vertical speed to correct the problem. However; due to the turbulence and descent rate at the time of the initial alert I wasn't confident that the aircraft would capture altitude hold at our clearance limit of FL290. I now believe that turning off all automation prior to the RA climb command with the poor weather and turbulence and the nose trimmed down for a rapid descent may have compounded the problem. I also could have set a more comfortable descent rate earlier by selecting vertical speed. Once I verified the automation was properly set; I made a poor decision to focus my attention to the arrival and approach charts when I should have been monitoring my primary flight instruments. After debriefing the event with the First Officer we agreed that we were caught off guard by the changing information being provided by TCAS. In the heat of the moment I remember hearing 'adjust vertical speed; adjust' and was not confident that the aircraft would capture FL290 due to the ride conditions. I made a split-second decision to disconnect automation and this may or may not have compounded the extreme workload we were experiencing.
At approximately FL315 we received a TCAS alert; 'traffic; monitor vertical speed.' Almost immediately followed by 'adjust vertical speed; adjust.' The Captain almost immediately disconnected the autopilot and autothrottles in order to comply with the alert.As he was doing this; I scaled down my map and mentioned the traffic is below us. As I was digesting the information I was seeing on the displays (while being bumped around quite a bit) I noticed the Captain was descending more rapidly than before the RA. It took me about two or three seconds of this before I corrected the Captain and told him we needed to climb not descend. I hesitated because I questioned myself on what I was actually seeing. As soon as I called out the error to the Captain; he corrected the attitude and complied with the RA.
B737-700 flight crew received an RA in descent at FL315 and the Captain was a bit slow to respond.