ACFT EQUIP PROB. ON ILS APCH; PITOT HEAT FAILED FOLLOWED BY RAPID AIRSPD DROP ON CAPT AIRSPD. THE ERRONEOUS AIRSPD IN THE AIR DATA COMPUTER; ADC; PUT ACFT IN THE AUTOMATIC 'ALPHA FLOOR' PROTECTION. AUTOTHROTTLES WENT TO MAX PWR (FOR AIRSPD RECOVERY). AUTOPLT WAS DISCONNECTED; ACFT PITCHED UP; OVERSPD FOR FLAP SETTING. FO TOOK OVER FLYING USING THE #2 ADC AND NORMAL LNDG ACCOMPLISHED.

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AIRSPD INPUT TO THE CAPT FLT DIRECTOR WENT BAD; PROBABLY DUE TO PROBE ICING. AIRSPD DECAY. AUTOFLT PROTECTION SYS COMMANDED MAX PWR. AIRSPD (ACTUAL) INCREASED RAPIDLY INTO OVERSPD RANGE FOR THE FLAP SETTING. ACFT WAS ALLOWED TO CLB FROM 4000 FT TO 6000 FT FOR AIRFRAME STRESS PROTECTION. AUTOTHROTTLES COULD NOT BE RECONNECTED. FO FLEW REMAINDER OF FLT ON HIS GOOD INSTS. OTHERWISE; NORMAL LNDG. SEEMS THERE'S A REAL NEED FOR SOME KIND OF COMPARATOR WARNINGS IN THESE AUTOFLT SYS. ACFT TYPE: A300-600F. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR CAPT SAYS AT FIRST HE THOUGHT THE PROB WAS A FAILED #1 ADC; BUT THEN REALIZED THAT THERE WAS A PITOT HEAT WARNING ALSO. THUS; HE BELIEVES THE PITOT HEAT FAILED; IT ICED UP GIVING AN ERRONEOUS AIRSPD; FOLLOWED BY THE ACFT ADC NOW BELIEVING THEY WERE APCHING A STALL; ALPHA FLOOR; AND THE AUTOTHROTTLES WENT TO FULL PWR. HOWEVER; THE AUTOPLT WAS STILL MAINTAINING THE ILS APCH UNTIL THE FLC DISCONNECTED IT; BUT BY THEN THE SPD HAD INCREASED RAPIDLY AND RESULTED IN AN OVERSPD FOR THE FLAP SETTING. RPTR NOTED THAT THERE WAS NO MAJOR TRIM PROB WITH THE ELEVATOR; THOUGH; AFTER DISCONNECTING THE AUTOPLT THE NOSE DID PITCH UP. BECAUSE OF THE EXCESSIVE AIRSPD FOR THE FLAP SETTING; THE FLC CHANGED PF; THE FO TOOK OVER THE CTLS BECAUSE THE #2 ADC WAS STILL GOOD AND THEY LET THE ACFT CLB TO DISSIPATE THE AIRSPD. THEN THEY DISCONNECTED THE AUTOTHROTTLES WITH THE MASTER SWITCH OFF AND APPARENTLY THAT RESULTED IN BEING UNABLE TO RECONNECT THE AUTOTHR OTTLES. RPTR SAYS THAT THEIR MANUAL DIDN'T INSTRUCT THEM TO TAKE ANY ACTION WHEN THE PITOT HEAT INOP CAME ON; BUT TO BE AWARE THAT THE AIRSPD MAY BE INACCURATE. HOWEVER; RPTR SAYS THAT AFTER GETTING FEEDBACK FROM HIS COMPANY SAFETY DEPT; THEY SAY THAT IN SOME PROC MANUALS THAT; WITH A PITOT FAIL; FLC'S ARE INSTRUCTED TO SELECT THE STANDBY ADC. THEIR MANUAL DOESN'T SAY THAT. ALSO; RPTR HAS SINCE FOUND THE PROC FOR GETTING THE AUTOTHROTTLES BACK AFTER DISCONNECTING WITH THE MASTER SWITCH. THAT INVOLVES RESETTING A CIRCUIT BREAKER.