Narrative:

It was my first officer's leg. He flew a perfectly normal ILS until about 50 ft AGL, then during the landing flare, the stall warning stick shaker pusher all activated. We were flying the correct vref speed. Apparently what happened is a wing leading edge sensor failed at the absolute worst time which faked the airplane into thinking we were in a deep stall. The first officer reacted instantaneously by jerking the nose back up and applying maximum power. We still hit the runway hard, but I'm convinced his instant reaction saved structural damage. At any higher altitude we could have gone around or at a lower altitude the airplane would have landed hard before an excessive sink rate developed. This is, by far, the most critical malfunction that I have seen in over 19000 hours of flight time. I thank god this did not happen during a low visibility CAT III autoland or on a short, wet, or slippery runway such as bur or sna. Callback conversation with reporter revealed the following information: the captain reports that all of the MD80 series have stick pushers. The MD80 series have mechanically actuated elevators with a tab system for actuation. The stick pusher, however, is hydraulically pwred, and takes a high force to overcome. This aircraft had a total of 3 incidents. After the reported incident, maintenance replaced the stall warning computer. The same incident occurred on the next flight, however, at a much higher altitude. Maintenance then adjusted the leading edge slat sensors. This did not help, as the false stall warning occurred again on the third flight. This time, maintenance replaced the leading edge slat sensor switches. No further incidents were reported.

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Original NASA ASRS Text

Title: MD83 CREW HAD STICK SHAKER AND STICK PUSHER ACTIVATE AT 50 FT AGL.

Narrative: IT WAS MY FO'S LEG. HE FLEW A PERFECTLY NORMAL ILS UNTIL ABOUT 50 FT AGL, THEN DURING THE LNDG FLARE, THE STALL WARNING STICK SHAKER PUSHER ALL ACTIVATED. WE WERE FLYING THE CORRECT VREF SPD. APPARENTLY WHAT HAPPENED IS A WING LEADING EDGE SENSOR FAILED AT THE ABSOLUTE WORST TIME WHICH FAKED THE AIRPLANE INTO THINKING WE WERE IN A DEEP STALL. THE FO REACTED INSTANTANEOUSLY BY JERKING THE NOSE BACK UP AND APPLYING MAX PWR. WE STILL HIT THE RWY HARD, BUT I'M CONVINCED HIS INSTANT REACTION SAVED STRUCTURAL DAMAGE. AT ANY HIGHER ALT WE COULD HAVE GONE AROUND OR AT A LOWER ALT THE AIRPLANE WOULD HAVE LANDED HARD BEFORE AN EXCESSIVE SINK RATE DEVELOPED. THIS IS, BY FAR, THE MOST CRITICAL MALFUNCTION THAT I HAVE SEEN IN OVER 19000 HRS OF FLT TIME. I THANK GOD THIS DID NOT HAPPEN DURING A LOW VISIBILITY CAT III AUTOLAND OR ON A SHORT, WET, OR SLIPPERY RWY SUCH AS BUR OR SNA. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE CAPT RPTS THAT ALL OF THE MD80 SERIES HAVE STICK PUSHERS. THE MD80 SERIES HAVE MECHANICALLY ACTUATED ELEVATORS WITH A TAB SYS FOR ACTUATION. THE STICK PUSHER, HOWEVER, IS HYDRAULICALLY PWRED, AND TAKES A HIGH FORCE TO OVERCOME. THIS ACFT HAD A TOTAL OF 3 INCIDENTS. AFTER THE RPTED INCIDENT, MAINT REPLACED THE STALL WARNING COMPUTER. THE SAME INCIDENT OCCURRED ON THE NEXT FLT, HOWEVER, AT A MUCH HIGHER ALT. MAINT THEN ADJUSTED THE LEADING EDGE SLAT SENSORS. THIS DID NOT HELP, AS THE FALSE STALL WARNING OCCURRED AGAIN ON THE THIRD FLT. THIS TIME, MAINT REPLACED THE LEADING EDGE SLAT SENSOR SWITCHES. NO FURTHER INCIDENTS WERE RPTED.

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.