BE35 PLT IS SHOCKED TO DISCOVER HIS ACFT HAS CLBED FROM 7500 FT TO APPROX 11000 FT WITHOUT REGISTERING THE CHANGE ON HIS PITOT STATIC INSTS WHICH TURNED OUT TO HAVE ICED UP. BECAME AWARE THROUGH RESEARCH OF MYSTERIOUSLY FALLING MANIFOLD PRESSURE WHICH LED HIM TO INVESTIGATE ALT READOUTS OF 2 GPS NAV SYS ON BOARD.

Narrative

LEG #3 OF ACFT DELIVERY (CHANGE OF OWNERSHIP) TO 0G7. ACFT PREVIOUSLY HAD BEEN BASED S FLORIDA FOR MORE THAN 3 MONTHS AND TIED DOWN OUTSIDE. CRUISE VFR FLT AT 7500 FT; RADAR ENRTE WITH ZDC (FLT FOLLOWING). SIT: ENG MANIFOLD INDICATION OBSERVED GRADUALLY DECREASING (15 MINS ESTIMATED INTERVAL) FROM FULL THROTTLE SETTING OF 22 INCHES; DETERIORATION CONTINUED TO 17 INCHES. FLT CONDITIONS CLR AND COLD (-10 DEGS C; OUTSIDE AIR TEMP). CARB HEAT APPLIED -- NO RELIEF. FLT INSTS NORMAL -- ALT INDICATING 7500 FT; STABLE. DECISION MADE TO DSND TO WARMER MORE DENSE AIR. DSCNT INITIATED AND DISCOVERED ALL PITOT STATIC INSTS FROZEN IN POS. AIRSPD ZERO. APPLIED PITOT HEAT -- NO IMMEDIATE CHANGE. CONSULTED BOTH GPS'S FOR BACK-UP FLT CONDITIONS AND FOUND ALT INDICATIONS OF ABOUT 11000 FT; GND SPD 89 KTS; OUTSIDE AIR TEMP WAS MUCH COLDER THAN PREVIOUSLY OBSERVED -20 DEGS C. INITIALLY I WAS INCREDULOUS CONCERNING GPS ALT INFO; BUT REALIZED IT ALL ADDED UP. WE HAD CLBED 3500 FT WITHOUT KNOWING IT. OUR ONLY INDICATION OF A PROB WAS DECREASING MANIFOLD INDICATIONS. CORRECTIVE ACTION: INFORMED ZDC OF PROB AND ALT. CONTINUED VFR FLT USING GPS ALT INDICATIONS DSNDING TO 7500 FT WHERE ENG INDICATIONS RETURNED TO NORMAL. ALL PITOT STATIC INDICATIONS REMAINED FROZEN; WITH THE EXCEPTION OF AIRSPD; WHICH STEADILY INCREASED TO FULL SCALE 250 KIAS. FLT COMPLETED TO 0G7 UNEVENTFULLY.