PLTS FAILED TO TURN ON PITOT HEAT IN WX.

Narrative

ALTHOUGH I'M A CFII WITH 150 PLUS HRS IN SEL COMPLEX; I ONLY HAD 3 HRS IN THIS ACFT (PA32R-300). I NEEDED MORE HRS TO SATISFY INSURANCE REQUIREMENTS FOR CHK-OUT; SO I FLEW AS L-SEAT PLT WITH A PROPERLY QUALIFIED AND CHKED- OUT CFII IN R-SEAT. ALTHOUGH IMC WAS FORECAST FOR RTE; NO ICE WAS FORECAST (I ASKED SPECIFICALLY DURING FSS WX BRIEF). AFTER I HAD HAND-FLOWN HARD IFR FOR 60 PLUS MINS AT 7000 AND 9000; I LET THE R-HAND CFII FLY FOR 10 MINS WHILE I RELAXED; REFOLDED MAPS; ETC. ACFT WAS CRUISING AT 160 MPH INDICATED. WHILE I WAS CHKING CHART TO RETUNE NAV RADIOS; R-HAND CFII REMARKED ON AIRSPD 70 MPH INDICATED! I CHKED L WING FOR ICE (YES); AND PITOT HEAT ON (NO!). I TURNED ON PITOT HEAT AND WAITED FOR AIRSPD TO INCREASE -- ALTIMETER STILL 9000! WHEN AIRSPD DROPPED TO 60-65 MPH; I ASKED ATC TO DSND TO 7000 FT 'NOW.' ATC WAS UNABLE DUE TO NO CTL OVER LOWER ALTS. I STATED ACFT WILL DSND TO 7000! NOW.' ATC ASKED IF I WAS DECLARING EMER AND I CONFIRMED 'AFFIRMATIVE.' AS WE DSNDED; AIRSPD INCREASED STEADILY; TO 180-190 MPH INDICATED; AND WE LEVELLED SMOOTHLY AT 7000! PASSING 7200 FT. I ADVISED ATC THAT PROB WAS RESOLVED AND ASSURED ATC 'NO NEED OF FURTHER ASSISTANCE.' FLT PROCEEDED ROUTINELY THEREAFTER; THOUGH WE OBTAINED APPROVAL TO DSND TO 5000 FT A FEW MINS LATER; TO REMOVE REMAINING ICE. NOTHING MORE WAS SAID ABOUT OUR BRIEF EMER. LEARNING CONCLUSIONS: 1) ALWAYS KEEP PITOT HEAT ON IN VISIBLE MOISTURE BELOW 40 DEGS F; EVEN IF ICE IS NOT FORECAST. 2) ALWAYS MONITOR YOUR INSTRUCTOR'S PERFORMANCE AS WELL AS YOU HOPE HE/SHE IS MONITORING YOURS!