Narrative:

It was my leg from cvg to phx. We had been in light rime icing with engine and wing anti-ice on for approximately 15 mins. We were just passing overhead tcc when my first officer noted our our airspeed was increasing. Our airspeed went from mach .82 to mach .845. Our nose started dropping, and we started losing about 1000'. At this time I told the first officer to contact center, and I disconnected the autoplt about 200' below FL310. I still did not suspect anything other than a mountain wave at that time. Vertical velocity increased to 2000 FPM down, while I pulled back on the yoke until it was full aft. Main trim, cruise trim and manual trim were all frozen. The first officer was hammering the manual trim wheel with both hands. The second officer was setting the power as I directed, while I was using both hands on the yoke to keep it full aft. The first officer finally broke loose the manual trim wheel. At this time, I was able to stop our descent at FL290 and start a slow climb to FL310. All trim eventually started working and the flight continued to phx. Callback conversation with reporter revealed the following: reporter stated that a frontal system had just been negotiated, with slight detours made for thunderstorm avoidance. Thunderstorms were at least 35-40 mi away with a fairly smooth ride. At first the PIC thought the initial downward motion was the normal action of a mountain wave, but upon a gentle pull back on the yoke noticed no stabilizer trim movement. After autoplt was disconnected, a steady back pressure resulted in a furthering of the descent rate. No trim was available from cruise trim, main electric trim motor or manual trim. The first officer had to hit the manual trim handle with his hands and eventually his foot to loosen it up. The total air temperature gauge indicated about a -5 degree centigrade to about 0, a good temperature for freezing. The horizontal stabilizer on this aircraft (a t-tail) has no anti-ice protection. Latitude trim was ok. Post-flight inspection revealed nothing, but maintenance changed the cruise trim motor and the main electric trim motor in phx before releasing the aircraft.

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Original NASA ASRS Text

Title: ALT DEVIATOIN ALT EXCURSION OCCURS AS STABILIZER TRIM BECOMES INOPERATIVE AFTER ENCOUNTERING RIME ICE BUILDUP AND A MOUNTAIN WAVE.

Narrative: IT WAS MY LEG FROM CVG TO PHX. WE HAD BEEN IN LIGHT RIME ICING WITH ENG AND WING ANTI-ICE ON FOR APPROX 15 MINS. WE WERE JUST PASSING OVERHEAD TCC WHEN MY F/O NOTED OUR OUR AIRSPD WAS INCREASING. OUR AIRSPD WENT FROM MACH .82 TO MACH .845. OUR NOSE STARTED DROPPING, AND WE STARTED LOSING ABOUT 1000'. AT THIS TIME I TOLD THE F/O TO CONTACT CENTER, AND I DISCONNECTED THE AUTOPLT ABOUT 200' BELOW FL310. I STILL DID NOT SUSPECT ANYTHING OTHER THAN A MOUNTAIN WAVE AT THAT TIME. VERT VELOCITY INCREASED TO 2000 FPM DOWN, WHILE I PULLED BACK ON THE YOKE UNTIL IT WAS FULL AFT. MAIN TRIM, CRUISE TRIM AND MANUAL TRIM WERE ALL FROZEN. THE F/O WAS HAMMERING THE MANUAL TRIM WHEEL WITH BOTH HANDS. THE S/O WAS SETTING THE PWR AS I DIRECTED, WHILE I WAS USING BOTH HANDS ON THE YOKE TO KEEP IT FULL AFT. THE F/O FINALLY BROKE LOOSE THE MANUAL TRIM WHEEL. AT THIS TIME, I WAS ABLE TO STOP OUR DSNT AT FL290 AND START A SLOW CLB TO FL310. ALL TRIM EVENTUALLY STARTED WORKING AND THE FLT CONTINUED TO PHX. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR STATED THAT A FRONTAL SYS HAD JUST BEEN NEGOTIATED, WITH SLIGHT DETOURS MADE FOR TSTM AVOIDANCE. TSTMS WERE AT LEAST 35-40 MI AWAY WITH A FAIRLY SMOOTH RIDE. AT FIRST THE PIC THOUGHT THE INITIAL DOWNWARD MOTION WAS THE NORMAL ACTION OF A MOUNTAIN WAVE, BUT UPON A GENTLE PULL BACK ON THE YOKE NOTICED NO STABILIZER TRIM MOVEMENT. AFTER AUTOPLT WAS DISCONNECTED, A STEADY BACK PRESSURE RESULTED IN A FURTHERING OF THE DSNT RATE. NO TRIM WAS AVAILABLE FROM CRUISE TRIM, MAIN ELECTRIC TRIM MOTOR OR MANUAL TRIM. THE F/O HAD TO HIT THE MANUAL TRIM HANDLE WITH HIS HANDS AND EVENTUALLY HIS FOOT TO LOOSEN IT UP. THE TOTAL AIR TEMP GAUGE INDICATED ABOUT A -5 DEG CENTIGRADE TO ABOUT 0, A GOOD TEMP FOR FREEZING. THE HORIZ STABILIZER ON THIS ACFT (A T-TAIL) HAS NO ANTI-ICE PROTECTION. LAT TRIM WAS OK. POST-FLT INSPECTION REVEALED NOTHING, BUT MAINT CHANGED THE CRUISE TRIM MOTOR AND THE MAIN ELECTRIC TRIM MOTOR IN PHX BEFORE RELEASING THE ACFT.

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.