Narrative:

On the ground I had a frozen spot somewhere in the static system. I turned on the pitot heat which solved the problem temporarily en route at 8000 ft, I thought I would try the alternate static to check out the system. At the time I checked it everything (altimeter, airspeed, and vertical speed indicator) were normal. On the alternate static (altimeter, airspeed, and vertical speed indicator) jumped like normal when switching. Then I went back to the normal static. A few seconds later, the airspeed was 40 KTS slower. Then center advised me I was 300 ft low. I asked them if they wanted me to stop my altitude squawk. They replied no. At the time I was showing 80 KTS exactly. Then I switched to the alternate static and the airspeed went back to normal, but the altimeter jumped to 8600 ft. I asked center what altitude they showed, because I didn't know which one to believe. Center replied 8400 ft. Then I told them about my static problem. They were not too concerned about altitude problem and did not ask me to do anything different. I learned that if the static system is working just fine, but you had a problem on the ground before takeoff, 'don't touch it.'

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Original NASA ASRS Text

Title: FROZEN STATIC LINE CAUSES SMT TO CLB 600 FT ABOVE ASSIGNED ALT WITH THE FLC UNAWARE.

Narrative: ON THE GND I HAD A FROZEN SPOT SOMEWHERE IN THE STATIC SYS. I TURNED ON THE PITOT HEAT WHICH SOLVED THE PROB TEMPORARILY ENRTE AT 8000 FT, I THOUGHT I WOULD TRY THE ALTERNATE STATIC TO CHK OUT THE SYS. AT THE TIME I CHKED IT EVERYTHING (ALTIMETER, AIRSPD, AND VERT SPD INDICATOR) WERE NORMAL. ON THE ALTERNATE STATIC (ALTIMETER, AIRSPD, AND VERT SPD INDICATOR) JUMPED LIKE NORMAL WHEN SWITCHING. THEN I WENT BACK TO THE NORMAL STATIC. A FEW SECONDS LATER, THE AIRSPD WAS 40 KTS SLOWER. THEN CTR ADVISED ME I WAS 300 FT LOW. I ASKED THEM IF THEY WANTED ME TO STOP MY ALT SQUAWK. THEY REPLIED NO. AT THE TIME I WAS SHOWING 80 KTS EXACTLY. THEN I SWITCHED TO THE ALTERNATE STATIC AND THE AIRSPD WENT BACK TO NORMAL, BUT THE ALTIMETER JUMPED TO 8600 FT. I ASKED CTR WHAT ALT THEY SHOWED, BECAUSE I DIDN'T KNOW WHICH ONE TO BELIEVE. CTR REPLIED 8400 FT. THEN I TOLD THEM ABOUT MY STATIC PROB. THEY WERE NOT TOO CONCERNED ABOUT ALT PROB AND DID NOT ASK ME TO DO ANYTHING DIFFERENT. I LEARNED THAT IF THE STATIC SYS IS WORKING JUST FINE, BUT YOU HAD A PROB ON THE GND BEFORE TKOF, 'DON'T TOUCH IT.'

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.