Narrative:

Location: runway 17 threshold. WX at scl reported as 400 meters and set up for CAT III approach. All procedures were performed as per company operations manual. On our first approach dual land green was achieved at approximately 1500 radio altimeter. At approximately 500 radio altimeter autoplt reverted to single land. A go around was performed and a briefing was done for CAT ii conditions with an autoland planned as per operations manual dual land green was again received, but changed to single land at approximately 500 ft AGL. All was normal until approximately 100 ft radio altimeter and nose pitched down. Autoplt was disconnected, but not enough time to keep the aircraft from hitting the runway. Aircraft contacted the runway with main gear first and bounced, we would have hit with the nose gear if we did not react. This is the second time this has occurred in this aircraft with me alone. First was with a check airman in frankfurt and now in santiago. This autoplt problem needs to be urgently addressed or we are going to damage one of our aircraft. In both instances the autoplt downgraded in the approach from dual land to single land. Both cases had a radio altimeter inoperative with no indications from the cockpit other than the single land indication. Our book states we can make an autoland with single land autoplt. We have to have 2 radio altimeters at the beginning of the approach, but can lose one and still continue. It is my opinion that this aircraft should not be allowed to do an autoland when the autoplt degrades from dual land to single land. Neither radio altimeter had an 'X' indicated in the window. I feel that autolands should be discontinued until this issue is settled. Supplemental information from acn 489263: during the landing phase of a single land approach to runway 17 scl at approximately 80, the aircraft pitched forward requiring the captain to take control. The approach was normal through 100 ft AGL except for the first officer's radio altimeter which cycled out of view at 800 and back at 600. During the pitch forward and subsequent recovery the aircraft's oral 50, 40, 30, 20, 10, calls were omitted.

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Original NASA ASRS Text

Title: DEGRADATION OF AUTOFLT SYS DURING APCH RESULTS IN LESS THAN DESIRABLE LNDG.

Narrative: LOCATION: RWY 17 THRESHOLD. WX AT SCL RPTED AS 400 METERS AND SET UP FOR CAT III APCH. ALL PROCS WERE PERFORMED AS PER COMPANY OPS MANUAL. ON OUR FIRST APCH DUAL LAND GREEN WAS ACHIEVED AT APPROX 1500 RADIO ALTIMETER. AT APPROX 500 RADIO ALTIMETER AUTOPLT REVERTED TO SINGLE LAND. A GAR WAS PERFORMED AND A BRIEFING WAS DONE FOR CAT II CONDITIONS WITH AN AUTOLAND PLANNED AS PER OPS MANUAL DUAL LAND GREEN WAS AGAIN RECEIVED, BUT CHANGED TO SINGLE LAND AT APPROX 500 FT AGL. ALL WAS NORMAL UNTIL APPROX 100 FT RADIO ALTIMETER AND NOSE PITCHED DOWN. AUTOPLT WAS DISCONNECTED, BUT NOT ENOUGH TIME TO KEEP THE ACFT FROM HITTING THE RWY. ACFT CONTACTED THE RWY WITH MAIN GEAR FIRST AND BOUNCED, WE WOULD HAVE HIT WITH THE NOSE GEAR IF WE DID NOT REACT. THIS IS THE SECOND TIME THIS HAS OCCURRED IN THIS ACFT WITH ME ALONE. FIRST WAS WITH A CHK AIRMAN IN FRANKFURT AND NOW IN SANTIAGO. THIS AUTOPLT PROB NEEDS TO BE URGENTLY ADDRESSED OR WE ARE GOING TO DAMAGE ONE OF OUR ACFT. IN BOTH INSTANCES THE AUTOPLT DOWNGRADED IN THE APCH FROM DUAL LAND TO SINGLE LAND. BOTH CASES HAD A RADIO ALTIMETER INOP WITH NO INDICATIONS FROM THE COCKPIT OTHER THAN THE SINGLE LAND INDICATION. OUR BOOK STATES WE CAN MAKE AN AUTOLAND WITH SINGLE LAND AUTOPLT. WE HAVE TO HAVE 2 RADIO ALTIMETERS AT THE BEGINNING OF THE APCH, BUT CAN LOSE ONE AND STILL CONTINUE. IT IS MY OPINION THAT THIS ACFT SHOULD NOT BE ALLOWED TO DO AN AUTOLAND WHEN THE AUTOPLT DEGRADES FROM DUAL LAND TO SINGLE LAND. NEITHER RADIO ALTIMETER HAD AN 'X' INDICATED IN THE WINDOW. I FEEL THAT AUTOLANDS SHOULD BE DISCONTINUED UNTIL THIS ISSUE IS SETTLED. SUPPLEMENTAL INFO FROM ACN 489263: DURING THE LNDG PHASE OF A SINGLE LAND APCH TO RWY 17 SCL AT APPROX 80, THE ACFT PITCHED FORWARD REQUIRING THE CAPT TO TAKE CTL. THE APCH WAS NORMAL THROUGH 100 FT AGL EXCEPT FOR THE FO'S RADIO ALTIMETER WHICH CYCLED OUT OF VIEW AT 800 AND BACK AT 600. DURING THE PITCH FORWARD AND SUBSEQUENT RECOVERY THE ACFT'S ORAL 50, 40, 30, 20, 10, CALLS WERE OMITTED.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.