Narrative:

We were on a flight from stl to msp. We had climbed out of stl in rain showers and a good portion of the way to our maximum altitude of FL310. When we leveled off at FL310 we were past the front and in the clear. Center then asked us to descend to FL290. After leveling at FL290 with the autoplt I noticed a significant airspeed differences on the pilot airspeed indicator. Then I noticed an altitude difference; the pilot's said FL290 but the copilot's said FL310. I notified center and asked for a block altitude. Or standby altimeter also showed FL310. In our descent it was later obvious that the pilot's static input must be blocked because the altitude and vsi stayed the same but airspeed increased unrealistically. When we got to a lower altitude the ice blocking the static line melted and instruments worked. There was no conflict involved and center thanked us for informing them. We did find water in the static line on the ground and drained it. Callback conversation with reporter revealed the following information. Reporter stated that there had been prior problems of this type reported by the manufacturer and that mods had been carried out to straighten bends in the pitot system and that there had not been any recent reports of such events. The pitot static port plate is heated but that does not take care of any frozen moisture downstream of that port. Post flight inspection revealed about a thimble full of water in system. Reporter stated that this particular model does not have the heated plates on the system. He further stated that there was a company (manufacturer) rep at the airport and he was going to press on him for a solution to this particular situation.

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Original NASA ASRS Text

Title: ICING OF THE PITOT STATIC SYS CREATES UNRELIABLE INST READINGS AFTER FLT THROUGH HVY RAIN ON CLB OUT.

Narrative: WE WERE ON A FLT FROM STL TO MSP. WE HAD CLBED OUT OF STL IN RAIN SHOWERS AND A GOOD PORTION OF THE WAY TO OUR MAX ALT OF FL310. WHEN WE LEVELED OFF AT FL310 WE WERE PAST THE FRONT AND IN THE CLR. CENTER THEN ASKED US TO DSND TO FL290. AFTER LEVELING AT FL290 WITH THE AUTOPLT I NOTICED A SIGNIFICANT AIRSPD DIFFERENCES ON THE PLT AIRSPD INDICATOR. THEN I NOTICED AN ALT DIFFERENCE; THE PLT'S SAID FL290 BUT THE COPLT'S SAID FL310. I NOTIFIED CENTER AND ASKED FOR A BLOCK ALT. OR STANDBY ALTIMETER ALSO SHOWED FL310. IN OUR DSCNT IT WAS LATER OBVIOUS THAT THE PLT'S STATIC INPUT MUST BE BLOCKED BECAUSE THE ALT AND VSI STAYED THE SAME BUT AIRSPD INCREASED UNREALISTICALLY. WHEN WE GOT TO A LOWER ALT THE ICE BLOCKING THE STATIC LINE MELTED AND INSTS WORKED. THERE WAS NO CONFLICT INVOLVED AND CENTER THANKED US FOR INFORMING THEM. WE DID FIND WATER IN THE STATIC LINE ON THE GND AND DRAINED IT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO. RPTR STATED THAT THERE HAD BEEN PRIOR PROBLEMS OF THIS TYPE RPTED BY THE MANUFACTURER AND THAT MODS HAD BEEN CARRIED OUT TO STRAIGHTEN BENDS IN THE PITOT SYS AND THAT THERE HAD NOT BEEN ANY RECENT RPTS OF SUCH EVENTS. THE PITOT STATIC PORT PLATE IS HEATED BUT THAT DOES NOT TAKE CARE OF ANY FROZEN MOISTURE DOWNSTREAM OF THAT PORT. POST FLT INSPECTION REVEALED ABOUT A THIMBLE FULL OF WATER IN SYS. RPTR STATED THAT THIS PARTICULAR MODEL DOES NOT HAVE THE HEATED PLATES ON THE SYS. HE FURTHER STATED THAT THERE WAS A COMPANY (MANUFACTURER) REP AT THE ARPT AND HE WAS GOING TO PRESS ON HIM FOR A SOLUTION TO THIS PARTICULAR SITUATION.

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.