C172 INSTRUCTOR TAKES STUDENT UP FOR AN ACTUAL INST CONDITIONS FLT RESULTING IN PICKING UP ACFT ICING AND LOSING CTL OF THE ACFT DURING A XWIND LNDG.

Narrative

A LCL IFR FLT WAS PLANNED TO DEMONSTRATE 'ACTUAL' CONDITIONS TO STUDENT. AIRMET FOR IFR COVERED THE AREA; BUT NONE FOR ICING. PIREPS CONTAINED NO RPTS OF ICING IN AREA. A PHONE CALL TO APCH CTL (ON OUR FIELD) RPTED NO ONE PICKING UP ICE AROUND OUR ARPT. DEPARTED FIELD; ENTERED CLOUDS AT 1000 FT AGL. AT AROUND 1800 FT AGL; TRACES OF RIME ICE BEGAN TO APPEAR. IMMEDIATELY REQUESTED LOWER ALT AND RETURN TO FIELD FOR ILS APCH. APPROX 1/4 INCH ICE ACCUMULATED ON LEADING EDGES; STRUTS AND TIRES DURING VECTORING FOR APCH. BROKE OUT ON APCH AT 1000 FT AGL. ICE BEGAN MELTING AND BLOWING OFF AIRPLANE. STUDENT CONTINUED APCH TO LNDG. WIND WAS QUARTERING HEADWIND FROM R; SO STUDENT SET UP FOR XWIND LNDG. DURING FLARE; THE L WING DROPPED WELL ABOVE STALL SPD AND THE AIRPLANE BEGAN A CORRESPONDING TURN TO THE L. I CALLED FOR PWR FOR A GAR BEFORE WE DEPARTED THE RWY; BUT AIRPLANE WOULD NOT CLB. AIRPLANE DEPARTED RWY TO THE L. I PULLED OFF THE PWR AND STOPPED THE ACFT. NO DAMAGE WAS DONE TO THE PLANE OR FIELD (LIGHTS; ETC). IN RETROSPECT; I MISJUDGED THE PERFORMANCE DEGRADATION FROM THE REMAINING ICE ON THE AIRFRAME. I KNEW FROM PAST READING THAT A HIGHER THAN NORMAL LNDG SPD; WITHOUT THE USE OF FLAPS; WAS THE PROPER APCH WITH AN ICED-UP AIRPLANE; AND I DID HALT MY STUDENT FROM EXTENDING THEM; BUT I WAS UNDER THE FALSE ASSUMPTION THAT THE ICE HAD EXITED THE PLANE; WHEN IN FACT IT HAD NOT ENTIRELY. I BELIEVE THAT A COMBINATION OF A HIGHER THAN NORMAL STALL SPD; COUPLED WITH A SMALL BLANKETING OF THE L WING DUE TO THE XWIND SIDESLIP; CAUSED THE L WING TO STALL. I HAVE LEARNED FROM THIS INCIDENT AN EVEN MORE HEALTHY RESPECT FOR ICE AND THE DEGRADED PERFORMANCE THAT IT CAN CAUSE. I HAVE LEARNED TO LAND WITH PLENTY OF EXTRA SPD SHOULD I EVER ENCOUNTER UNFORECAST ICE AGAIN; AND TO FLARE AS LOW AS POSSIBLE. I HAVE OFTEN READ; AND NOW SEEN; THAT ANY ICE -- EVEN A 'SMALL' ACCUMULATION -- CAN CAUSE COMPLETELY UNPREDICTABLE AERODYNAMIC CONSEQUENCES.