Narrative:

En route from rdm to sfo, the first officer was the PF, I was performing the PNF duties. Assigned by ATC to 16,000' and advised to expect 15,000' shortly, we were level at 16,000' and cruising in light turbulence and light icing conditions. I left the cockpit to secure an overhead passenger service console that had been knocked loose in flight by turbulence that was reported to me by the F/a. I secured the overhead panel with a screw driver I had in my flight bag and returned to the cockpit. Upon return to the cockpit I checked with the first officer and evaluated the flight conditions. The first officer advised me that ATC had cleared us to 15,000' and we were level at 15,000'. The flight conditions at 15,000' were found to be light turbulence and light mixed rime and clear ice. I left the first officer at the controls to use the lavatory. Returning to the cockpit, I noticed we were encountering an area of mod precipitation. As I was getting back into my seat I noticed a rapid decrease in airspeed from 180 K to 160 K. I told the first officer to increase power and he began to do so, at the same time I observed the fast/slow indicator to show a decrease in speed and the stall warning stick shaker to activate. I immediately took control of the aircraft, transferred the autoplt to regain manual control of the aircraft and applied maximum power to recover from the imminent stall and advised the first officer to ask for a lower altitude. At this point the aircraft began to roll left 30 degree then right 30-40 degree twice. During this time I was working to maintain a wings level attitude and altitude of the aircraft. Due to apparently the rapid accretion of rime ice on the wings and turbulence we had encountered upon entering the area of precipitation and heavy icing, we descended to 11,700' before fully stabilizing the aircraft. ATC advised that 9300' was his min vectoring altitude in this area and asked what were our intentions. We requested 12,000'. ATC cleared us to 12,000' and asked what was our requested routing. Upon stabilizing the aircraft at 12,000' and evaluating the situation, we advised ATC that we were requesting to continue to SFL. ATC cleared us direct lmt as filed 12,000' to sfo. I questioned the seattle center controller if any written report to him was required concerning this incident. He advised me that there was no report required. I advised him that I would in fact be reporting this incident in writing to the company. The controller advised me that he would note heavy rime icing and turbulence in the computer as a PIREP. The F/a reported that the cabin was secure, and that all the passenger were ok. I made a PA to the passenger of the icing and turbulence we had encountered explaining our rapid descent and apologizing for the conditions. I asked the passenger to advise the F/a should they have any immediate needs and that we would be continuing to sfo. The flight continued without incident to sfo. Checking in with sfo operations for the rdm WX, I found no message to contact the company or ATC concerning this incident. Being late for departure we serviced and preflted the aircraft and departed back to rdm.

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Original NASA ASRS Text

Title: ALT DEVIATION DUE TO ICING AND TURBULENCE. BRIEF LOSS OF ACFT CONTROL.

Narrative: ENRTE FROM RDM TO SFO, THE F/O WAS THE PF, I WAS PERFORMING THE PNF DUTIES. ASSIGNED BY ATC TO 16,000' AND ADVISED TO EXPECT 15,000' SHORTLY, WE WERE LEVEL AT 16,000' AND CRUISING IN LIGHT TURBULENCE AND LIGHT ICING CONDITIONS. I LEFT THE COCKPIT TO SECURE AN OVERHEAD PAX SERVICE CONSOLE THAT HAD BEEN KNOCKED LOOSE IN FLT BY TURBULENCE THAT WAS REPORTED TO ME BY THE F/A. I SECURED THE OVERHEAD PANEL WITH A SCREW DRIVER I HAD IN MY FLT BAG AND RETURNED TO THE COCKPIT. UPON RETURN TO THE COCKPIT I CHECKED WITH THE F/O AND EVALUATED THE FLT CONDITIONS. THE F/O ADVISED ME THAT ATC HAD CLRED US TO 15,000' AND WE WERE LEVEL AT 15,000'. THE FLT CONDITIONS AT 15,000' WERE FOUND TO BE LIGHT TURBULENCE AND LIGHT MIXED RIME AND CLEAR ICE. I LEFT THE F/O AT THE CONTROLS TO USE THE LAVATORY. RETURNING TO THE COCKPIT, I NOTICED WE WERE ENCOUNTERING AN AREA OF MOD PRECIPITATION. AS I WAS GETTING BACK INTO MY SEAT I NOTICED A RAPID DECREASE IN AIRSPEED FROM 180 K TO 160 K. I TOLD THE F/O TO INCREASE POWER AND HE BEGAN TO DO SO, AT THE SAME TIME I OBSERVED THE FAST/SLOW INDICATOR TO SHOW A DECREASE IN SPEED AND THE STALL WARNING STICK SHAKER TO ACTIVATE. I IMMEDIATELY TOOK CONTROL OF THE ACFT, TRANSFERRED THE AUTOPLT TO REGAIN MANUAL CONTROL OF THE ACFT AND APPLIED MAX POWER TO RECOVER FROM THE IMMINENT STALL AND ADVISED THE F/O TO ASK FOR A LOWER ALT. AT THIS POINT THE ACFT BEGAN TO ROLL LEFT 30 DEG THEN RIGHT 30-40 DEG TWICE. DURING THIS TIME I WAS WORKING TO MAINTAIN A WINGS LEVEL ATTITUDE AND ALT OF THE ACFT. DUE TO APPARENTLY THE RAPID ACCRETION OF RIME ICE ON THE WINGS AND TURBULENCE WE HAD ENCOUNTERED UPON ENTERING THE AREA OF PRECIPITATION AND HEAVY ICING, WE DESCENDED TO 11,700' BEFORE FULLY STABILIZING THE ACFT. ATC ADVISED THAT 9300' WAS HIS MIN VECTORING ALT IN THIS AREA AND ASKED WHAT WERE OUR INTENTIONS. WE REQUESTED 12,000'. ATC CLRED US TO 12,000' AND ASKED WHAT WAS OUR REQUESTED ROUTING. UPON STABILIZING THE ACFT AT 12,000' AND EVALUATING THE SITUATION, WE ADVISED ATC THAT WE WERE REQUESTING TO CONTINUE TO SFL. ATC CLRED US DIRECT LMT AS FILED 12,000' TO SFO. I QUESTIONED THE SEATTLE CENTER CTLR IF ANY WRITTEN REPORT TO HIM WAS REQUIRED CONCERNING THIS INCIDENT. HE ADVISED ME THAT THERE WAS NO REPORT REQUIRED. I ADVISED HIM THAT I WOULD IN FACT BE REPORTING THIS INCIDENT IN WRITING TO THE COMPANY. THE CTLR ADVISED ME THAT HE WOULD NOTE HEAVY RIME ICING AND TURBULENCE IN THE COMPUTER AS A PIREP. THE F/A REPORTED THAT THE CABIN WAS SECURE, AND THAT ALL THE PAX WERE OK. I MADE A PA TO THE PAX OF THE ICING AND TURBULENCE WE HAD ENCOUNTERED EXPLAINING OUR RAPID DSCNT AND APOLOGIZING FOR THE CONDITIONS. I ASKED THE PAX TO ADVISE THE F/A SHOULD THEY HAVE ANY IMMEDIATE NEEDS AND THAT WE WOULD BE CONTINUING TO SFO. THE FLT CONTINUED WITHOUT INCIDENT TO SFO. CHECKING IN WITH SFO OPS FOR THE RDM WX, I FOUND NO MESSAGE TO CONTACT THE COMPANY OR ATC CONCERNING THIS INCIDENT. BEING LATE FOR DEP WE SERVICED AND PREFLTED THE ACFT AND DEPARTED BACK TO RDM.

Data retrieved from NASA's ASRS site as of August 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.