MAKING A CAT III AUTOLAND; ACFT LANDED VERY HARD. DURING APCH FLC HAD A 'NAV ACCURACY DOWNGRADE' FOLLOWED SHORTLY BY 'NAV ACCURACY UPGRADE.' RPTR THOUGHT THE MESSAGES SHOULD NOT AFFECT THE APCH.

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WE SET UP FOR AN AUTOLAND ON RWY 16R AT SEA. WX WAS GOOD VFR WITH WIND DOWN THE RWY AT APPROX 150 DEGS AND 9 KTS. WE ADVISED APCH CTL THAT WE WISHED TO MAKE A COUPLED APCH AND AUTOLAND. THE FINAL WAS APPROX 10 MI LONG AND LOC AND GS CAPTURE WENT SMOOTHLY. THE ACFT WAS CONFIGURED EARLY AND WAS ON SPD AND ON PROFILE. WE HAD A NAV ACCURACY DOWNGRADE DISPLAYED FOR A MOMENT FOLLOWED BY A NAV ACCURACY UPGRADE MESSAGE AT ABOUT A 5 MI FINAL. I FELT THAT THESE MESSAGES SHOULD NOT AFFECT THE APCH SINCE WE WERE USING ILS LOC AND GS NAV AND NOT FMGS COMPUTED NAV. ALL FMA ANNUNCIATIONS WERE NORMAL. I BROUGHT THE THROTTLES TO IDLE AT THE 'RETARD' CALLOUT. THE ACFT FLARED EXCESSIVELY HIGH (MAYBE 10 FT) AND THEN LOWERED THE NOSE FOLLOWED BY A HARD TOUCHDOWN; A BOUNCE; AND A SECOND HARD TOUCHDOWN. IT WAS THE WORST LNDG I HAVE EVER EXPERIENCED AS A PLT OR PAX ON THIS AIRLINE. AT THE SUGGESTION OF THE FAA INSPECTOR ON THE JUMPSEAT WE REQUESTED A HARD LNDG INSPECTION WHICH REVEALED NO DAMAGE. THE FO AND I DISCUSSED THE INCIDENT AND COULD THINK OF NO REASON WHY THIS SHOULD NOT HAVE BEEN A ROUTINE AUTOLAND UNDER NEARLY IDEAL CONDITIONS. I JUST COMPLETED ANOTHER TRIP WITH AN EXPERIENCED FO WHO STATED THAT THE ONLY AUTOLAND THAT HAD EVER MADE HIM UNCOMFORTABLE WAS ON RWY 16R AT SEA WHEN THE AIRPLANE FLARED EXCESSIVELY HIGH. I DO NOT KNOW IF THIS IS AN ACFT PROB OR A RWY PROB; BUT BASED ON THIS EXPERIENCE I DO NOT BELIEVE THAT THE A320 SHOULD AUTOLAND ON SEA RWY 16R PENDING FURTHER INVESTIGATION.