Narrative:

This was the final leg of a long three leg day. Prior to departure I briefed the flight attendants about turbulence on the climb out and into den and that I was going to have them clean up before our descent. Ten minutes to push a maintenance issue came up and lead to an aircraft swap. Due to the delay my flight attendant briefing was now almost two hours old. With the aircraft swap everyone was busy and there were a lot of distractions with passengers who left things on the other aircraft. We were filed for FL310 to bypass the turbulence plot areas and the flight was smooth at 310. As we passed ocs (rock springs) we started to get light chop and requested FL290 and the ride was smooth. Thirty minutes to top of descent I called the flight attendant to give them a thirty minute warning prior to descent and have the cabin secured. Again at ten minutes prior to top of descent I called the flight attendant and told them we start down in ten minutes. At top of descent I made an announcement to the passengers that we might encounter turbulence in the descent into den and I was turning on the seatbelt sign. Also made the' flight attendant prepare cabin for arrival call at this time' announcement. Descent was smooth and the weather clear there were no adverse ride reports being broadcast by other aircraft and approach control did not mention any ride reports -also approach deleted the speed restriction at ramms intersection on the arrival. We were also notified the ATIS had changed and told us to pick up the new ATIS and advise. I put that off until workload permitted. Approaching FL190 I gave the double chime. Approaching ramms the controller cleared us to 130 all checklist were complete and I went heads down to get the ATIS off ACARS - it came back as digital ATIS unavailable so I tried it again same thing. As I was looking up the ATIS frequency to dial it in we were passing 150. In a matter of four to five seconds we went from smooth to severe turbulence. First officer went to a wings level attitude and was pulling power back as airspeed was increasing I saw the green acceleration bar heading for the barber pole so I extended the speed brakes to add drag and stop the acceleration (the first officer had his hands full flying the aircraft). We exceeded barber pole by about five knots for approximately three to four seconds - we were in clean configuration; severe turbulence lasted for thirty to fourty seconds. We did not feel that we exceeded G limits. Reported severe turbulence to ATC - he then cleared us to 110. Out of 130 the severe subsided to moderate and smoothed out at 110. The rest of the arrival and approach was smooth. Once the ride smoothed out I called back to the flight attendant to see if we had any injuries - at that time I heard that one of them had hurt her arm. I called operations to have them notify paramedics to meet the aircraft. I did not declare an emergency or ask for priority handling as we were already on down wind and were number one for the approach - we were on the ground shortly there after. On block in the paramedics took care of the injured flight attendant. No passengers were hurt. I contacted dispatch; maintenance control and the duty officer and we had a conference call. Appropriate log book entries were made and I debriefed the mechanic who met the aircraft. As I reflect back on this event and what could we have done differently and what were the events that led up to this. If I had to point to one common thread it was creeping fatigue. I tied together two other as soon as possible reports as they warranted separate write-ups but they contributed to the chain of events. 1. I was surprised that the flight attendants were still doing a final walk through I had assumed that the cabin was all secure. But I also now realize that we started our descent from 290 instead of the usual 370 or higher. Based on standard rates of descent we were into the severe approximately five to seven minutes after the descent began. So I have to ask myself did my instructions match the intentions. When told to have the cabin picked up and secured for descent I assumed they would be seated. This points to careful choice of words. 2. I could have been more pro active with approach about rides. Since there were no complaints on frequency and the controller did not mention rides; and deleted the speed restriction at ramms; I assumed the rides would be ok. The paper work had turbulence forecast but all were up high and there was one that was down low but it expired a couple hours before our arrival and the smooth descent seemed to be playing that out. I recognize now that assuming and not being proactive are subtle signs of fatigue in myself. Our flight attendants did a great job and were very professional. We were over nine hours on duty before leaving for den. We were scheduled for eight hours of flying that day.

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Original NASA ASRS Text

Title: A B737 encountered severe turbulence passing 15;000 FT during descent into DEN causing injuries to flight attendants.

Narrative: This was the final leg of a long three leg day. Prior to departure I briefed the Flight Attendants about turbulence on the climb out and into DEN and that I was going to have them clean up before our descent. Ten minutes to push a maintenance issue came up and lead to an aircraft swap. Due to the delay my flight attendant briefing was now almost two hours old. With the aircraft swap everyone was busy and there were a lot of distractions with passengers who left things on the other aircraft. We were filed for FL310 to bypass the turbulence plot areas and the flight was smooth at 310. As we passed OCS (Rock Springs) we started to get light chop and requested FL290 and the ride was smooth. Thirty minutes to top of descent I called the Flight Attendant to give them a thirty minute warning prior to descent and have the cabin secured. Again at ten minutes prior to top of descent I called the Flight Attendant and told them we start down in ten minutes. At top of descent I made an announcement to the passengers that we might encounter turbulence in the descent into DEN and I was turning on the seatbelt sign. Also made the' Flight Attendant prepare cabin for arrival call at this time' announcement. Descent was smooth and the weather clear there were no adverse ride reports being broadcast by other aircraft and Approach Control did not mention any ride reports -also Approach deleted the speed restriction at RAMMS intersection on the arrival. We were also notified the ATIS had changed and told us to pick up the new ATIS and advise. I put that off until workload permitted. Approaching FL190 I gave the double chime. Approaching RAMMS the Controller cleared us to 130 all checklist were complete and I went heads down to get the ATIS off ACARS - it came back as digital ATIS unavailable so I tried it again same thing. As I was looking up the ATIS frequency to dial it in we were passing 150. In a matter of four to five seconds we went from smooth to severe turbulence. First Officer went to a wings level attitude and was pulling power back as airspeed was increasing I saw the green acceleration bar heading for the barber pole so I extended the speed brakes to add drag and stop the acceleration (the First Officer had his hands full flying the aircraft). We exceeded barber pole by about five knots for approximately three to four seconds - we were in clean configuration; severe turbulence lasted for thirty to fourty seconds. We did not feel that we exceeded G limits. Reported Severe Turbulence to ATC - he then cleared us to 110. Out of 130 the severe subsided to moderate and smoothed out at 110. The rest of the arrival and approach was smooth. Once the ride smoothed out I called back to the Flight Attendant to see if we had any injuries - at that time I heard that one of them had hurt her arm. I called Operations to have them notify paramedics to meet the aircraft. I did not declare an emergency or ask for priority handling as we were already on down wind and were number one for the approach - we were on the ground shortly there after. On block in the paramedics took care of the injured Flight Attendant. No passengers were hurt. I contacted Dispatch; Maintenance Control and the Duty Officer and we had a conference call. Appropriate log book entries were made and I debriefed the mechanic who met the aircraft. As I reflect back on this event and what could we have done differently and what were the events that led up to this. If I had to point to one common thread it was creeping fatigue. I tied together two other ASAP reports as they warranted separate write-ups but they contributed to the chain of events. 1. I was surprised that the flight attendants were still doing a final walk through I had assumed that the cabin was all secure. But I also now realize that we started our descent from 290 instead of the usual 370 or higher. Based on standard rates of descent we were into the severe approximately five to seven minutes after the descent began. So I have to ask myself did my instructions match the intentions. When told to have the cabin picked up and secured for descent I assumed they would be seated. This points to careful choice of words. 2. I could have been more pro active with Approach about rides. Since there were no complaints on frequency and the Controller did not mention rides; and deleted the speed restriction at RAMMS; I assumed the rides would be OK. The paper work had turbulence forecast but all were up high and there was one that was down low but it expired a couple hours before our arrival and the smooth descent seemed to be playing that out. I recognize now that assuming and not being proactive are subtle signs of fatigue in myself. Our flight attendants did a great job and were very professional. We were over nine hours on duty before leaving for DEN. We were scheduled for eight hours of flying that day.

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.