Narrative:

The situation began on descent into dsm from den. En route WX was smooth with some mid and high level cloudiness with occasional light turbulence. Over dsm, however, was a large thunderstorm of at least level 3 or 4. Wet tops as scanned by our wxr-700X radar were at least 40000'. Heavy rain was being reported at the airport and approachs were not being accepted and we were directed to hold at the dsm 320 degree/30 NM fix at FL190. A second, smaller cell was growing to the southwest of the large cell with smaller cumulus clouds southwest of the 2 cells. Our holding location was right along the trailing edge of the large cell and appeared visually to put us into some broken clouds showing vertical development above us. We elected to ask for a hold at the dsm 320 degree/40 NM, but frequency congestion did not allow the request until entering the clouds. Short term severe turbulence was encountered (10-15 seconds) while turning outbnd in the hold and in cloud. Shortly after breaking out into smooth air, our 40 NM hold was approved. Just prior to entering the new hold, we were given a turn to 140 degrees and descent to (I believe) 11000' for vectors to the ILS 12L at dsm. Shortly thereafter, we were handed off to dsm approach. We did not like the looks of the WX between us and the airport and radar showed the airport to be in about a 5 NM corridor between the 2 cells. In addition, the smaller cell had grown rapidly. We told approach we would go back and hold or take delay vectors at their convenience. We were given a vector of 180 degrees (I believe), but requested 200 degrees and were told to deviate as necessary. During this time, the wind shifted to favor 30R. The controller gave us a heading of 160 degrees (I believe) and a descent to 6000'. We asked for 10000' to stay on top of broken cumulus. We were given pilot's discretion to 6000' and leveled at 10000'. I lose track of the vectors at this point, but we were eventually in the position to turn inbound for the 30R ILS. While the airport was reporting light winds and light rain, our radar indicated the airport to be almost dead center in the cell. We rejected the approach, but came around to about 220 or 240 degrees to continue the delay vectors. It became clear at this point that we had erred in coming around to the southeast of the short line of 2 cells with broken cumulus to the southwest. The cumulus was now building rapidly and consolidating. Tops were now well above our 10000' and we requested 15000'. We were told to stand by for center coordination. We asked to deviate as necessary, which was approved. The cumulus ahead was not painting on radar at our altitude. We tilted up 10 degrees and started painting building precipitation above us. At this point we were cleared to 15000', and as we started the climb we entered the clouds. Turbulence was moderate to severe. Out of about 13000' the aircraft pitched us mildly and airspeed started to decay rapidly (below clean maneuvering. Autoplt. Response did not appear suitable, so I disconnected it, pitched over gently and added thrust. Airspeed responded to this action, as I noticed we were climbed through 14000' with the rate of climb pegged over 6000 FPM. I continued to pitch over and brought the thrust to idle. We went through 15000' at idle thrust, accelerating through 230 KTS and approximately 5 degree nose down pitch. The controller admonished us to level at 15000', and we responded that we were trying to but were in a strong updraft. At this point we broke out in the clear, in smooth air. The climb ceased at about 15400', and we immediately returned to 15000'. The winds had now shifted again and, after another period of heavy rain, the airport was landing on 12L. We were cleared for the approach and landed west/O further incident. With hindsight being 20/20, we would have been much better off holding at 190 at the dsm 320/40. It would have contributed to fuel conservation, a possibly earlier arrival and, of course, no altitude bust. Failing that, I should have listened more intently to my inner discomfort as we flew over the developing cumulus line the first time. One factor that contributed to the situation was a desire to stay within dsm approach airspace so that we could stay up with airport conditions more readily. As it turned out, a second frequency would have worked out better with only a slight increase in workload.

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Original NASA ASRS Text

Title: ALT DEVIATION ALT OVERSHOT WHEN ACR ACFT ENCOUNTERS TSTM ACTIVITY AND SUFFERS A TEMPORARY LOSS OF ACFT CTL.

Narrative: THE SITUATION BEGAN ON DSNT INTO DSM FROM DEN. ENRTE WX WAS SMOOTH WITH SOME MID AND HIGH LEVEL CLOUDINESS WITH OCCASIONAL LIGHT TURB. OVER DSM, HOWEVER, WAS A LARGE TSTM OF AT LEAST LEVEL 3 OR 4. WET TOPS AS SCANNED BY OUR WXR-700X RADAR WERE AT LEAST 40000'. HEAVY RAIN WAS BEING RPTED AT THE ARPT AND APCHS WERE NOT BEING ACCEPTED AND WE WERE DIRECTED TO HOLD AT THE DSM 320 DEG/30 NM FIX AT FL190. A SECOND, SMALLER CELL WAS GROWING TO THE SW OF THE LARGE CELL WITH SMALLER CUMULUS CLOUDS SW OF THE 2 CELLS. OUR HOLDING LOCATION WAS RIGHT ALONG THE TRAILING EDGE OF THE LARGE CELL AND APPEARED VISUALLY TO PUT US INTO SOME BROKEN CLOUDS SHOWING VERT DEVELOPMENT ABOVE US. WE ELECTED TO ASK FOR A HOLD AT THE DSM 320 DEG/40 NM, BUT FREQ CONGESTION DID NOT ALLOW THE REQUEST UNTIL ENTERING THE CLOUDS. SHORT TERM SEVERE TURB WAS ENCOUNTERED (10-15 SECS) WHILE TURNING OUTBND IN THE HOLD AND IN CLOUD. SHORTLY AFTER BREAKING OUT INTO SMOOTH AIR, OUR 40 NM HOLD WAS APPROVED. JUST PRIOR TO ENTERING THE NEW HOLD, WE WERE GIVEN A TURN TO 140 DEGS AND DSNT TO (I BELIEVE) 11000' FOR VECTORS TO THE ILS 12L AT DSM. SHORTLY THEREAFTER, WE WERE HANDED OFF TO DSM APCH. WE DID NOT LIKE THE LOOKS OF THE WX BTWN US AND THE ARPT AND RADAR SHOWED THE ARPT TO BE IN ABOUT A 5 NM CORRIDOR BTWN THE 2 CELLS. IN ADDITION, THE SMALLER CELL HAD GROWN RAPIDLY. WE TOLD APCH WE WOULD GO BACK AND HOLD OR TAKE DELAY VECTORS AT THEIR CONVENIENCE. WE WERE GIVEN A VECTOR OF 180 DEGS (I BELIEVE), BUT REQUESTED 200 DEGS AND WERE TOLD TO DEVIATE AS NECESSARY. DURING THIS TIME, THE WIND SHIFTED TO FAVOR 30R. THE CTLR GAVE US A HDG OF 160 DEGS (I BELIEVE) AND A DSNT TO 6000'. WE ASKED FOR 10000' TO STAY ON TOP OF BROKEN CUMULUS. WE WERE GIVEN PLT'S DISCRETION TO 6000' AND LEVELED AT 10000'. I LOSE TRACK OF THE VECTORS AT THIS POINT, BUT WE WERE EVENTUALLY IN THE POS TO TURN INBND FOR THE 30R ILS. WHILE THE ARPT WAS RPTING LIGHT WINDS AND LIGHT RAIN, OUR RADAR INDICATED THE ARPT TO BE ALMOST DEAD CENTER IN THE CELL. WE REJECTED THE APCH, BUT CAME AROUND TO ABOUT 220 OR 240 DEGS TO CONTINUE THE DELAY VECTORS. IT BECAME CLR AT THIS POINT THAT WE HAD ERRED IN COMING AROUND TO THE SE OF THE SHORT LINE OF 2 CELLS WITH BROKEN CUMULUS TO THE SW. THE CUMULUS WAS NOW BUILDING RAPIDLY AND CONSOLIDATING. TOPS WERE NOW WELL ABOVE OUR 10000' AND WE REQUESTED 15000'. WE WERE TOLD TO STAND BY FOR CENTER COORD. WE ASKED TO DEVIATE AS NECESSARY, WHICH WAS APPROVED. THE CUMULUS AHEAD WAS NOT PAINTING ON RADAR AT OUR ALT. WE TILTED UP 10 DEGS AND STARTED PAINTING BUILDING PRECIPITATION ABOVE US. AT THIS POINT WE WERE CLRED TO 15000', AND AS WE STARTED THE CLB WE ENTERED THE CLOUDS. TURB WAS MODERATE TO SEVERE. OUT OF ABOUT 13000' THE ACFT PITCHED US MILDLY AND AIRSPD STARTED TO DECAY RAPIDLY (BELOW CLEAN MANEUVERING. AUTOPLT. RESPONSE DID NOT APPEAR SUITABLE, SO I DISCONNECTED IT, PITCHED OVER GENTLY AND ADDED THRUST. AIRSPD RESPONDED TO THIS ACTION, AS I NOTICED WE WERE CLBED THROUGH 14000' WITH THE RATE OF CLB PEGGED OVER 6000 FPM. I CONTINUED TO PITCH OVER AND BROUGHT THE THRUST TO IDLE. WE WENT THROUGH 15000' AT IDLE THRUST, ACCELERATING THROUGH 230 KTS AND APPROX 5 DEG NOSE DOWN PITCH. THE CTLR ADMONISHED US TO LEVEL AT 15000', AND WE RESPONDED THAT WE WERE TRYING TO BUT WERE IN A STRONG UPDRAFT. AT THIS POINT WE BROKE OUT IN THE CLR, IN SMOOTH AIR. THE CLB CEASED AT ABOUT 15400', AND WE IMMEDIATELY RETURNED TO 15000'. THE WINDS HAD NOW SHIFTED AGAIN AND, AFTER ANOTHER PERIOD OF HEAVY RAIN, THE ARPT WAS LNDG ON 12L. WE WERE CLRED FOR THE APCH AND LANDED W/O FURTHER INCIDENT. WITH HINDSIGHT BEING 20/20, WE WOULD HAVE BEEN MUCH BETTER OFF HOLDING AT 190 AT THE DSM 320/40. IT WOULD HAVE CONTRIBUTED TO FUEL CONSERVATION, A POSSIBLY EARLIER ARR AND, OF COURSE, NO ALT BUST. FAILING THAT, I SHOULD HAVE LISTENED MORE INTENTLY TO MY INNER DISCOMFORT AS WE FLEW OVER THE DEVELOPING CUMULUS LINE THE FIRST TIME. ONE FACTOR THAT CONTRIBUTED TO THE SITUATION WAS A DESIRE TO STAY WITHIN DSM APCH AIRSPACE SO THAT WE COULD STAY UP WITH ARPT CONDITIONS MORE READILY. AS IT TURNED OUT, A SECOND FREQ WOULD HAVE WORKED OUT BETTER WITH ONLY A SLIGHT INCREASE IN WORKLOAD.

Data retrieved from NASA's ASRS site as of July 2007 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.