Narrative:

We were flying air carrier flight xyz from seattle to los angeles on nov/sat/98. We were cleared for a visual approach to runway 24R at lax. In the landing flare, trimmed at vref at approximately 50 ft AGL, the aural stall warning, stick shaker and stick pusher all activated. Autothrottles on, autoplt off. We were on a stabilized visual approach, 5+ mi separated between us and the aircraft ahead of us. The aircraft that we were following was a non-heavy turbojet (exact type unknown). Winds were light and no reported windshear in the area. The aircraft weighed 122000 pounds. We had the speed bugs set using the V speed reference card data for our flaps 40 degrees landing which results in a vref speed of 128 KTS. It is our airline's standard procedure to set the autothrottle speed reference window to vref +5 KTS. The resultant speed set in the autothrottle speed select window was 133 KTS. I (the first officer) was the PF and the captain was doing the standard PNF's duties which at the time of the incident included calling out airspds and sink rates. Since there was no windshear reported, no wake turbulence, no wind gusts, and no abnormal indications of any sort it was quite an unexpected and very surprising experience. The pitch attitude was normal, the indicated airspeed was normal, the power setting was normal and the autothrottles were on. Since we are trained to always respect stick shaker in windshear recovery and stall recovery training, in the simulator, I was very reluctant to increase my pitch attitude as I would normally do approaching the landing flare phase of flight. However, because of our very close proximity to the ground (approximately 50 ft AGL) I was not in a position to trade any pitch attitude for decreased angle of attack as I felt that this would result in possible airframe damage due to excessive sink rate. My only other option was to add power, lots of it, all the way to the mechanical stops, which I did. We contacted the runway in a firm landing and wrote up the stall warning system in the maintenance log. I performed a thorough postflt inspection of the aircraft along with a mechanic. Nothing abnormal observed. Maintenance replaced one of the stall warning computers and one of the aoa vanes and inhibited the stick pusher system and released the aircraft to service using appropriate MEL procedures. What caused this? I'm not sure, perhaps the next crew's experience will shed some light on the subject. The next crew, while on approach to the puerto vallarta airport observed a slat disagree light while on approach to the airport. The slat disagree light illuminated early enough in the approach to allow the crew time to follow the QRH procedures for the slat disagree light illuminated procedure. They were able to land without further incident and have maintenance performed on the aircraft. In our case, although we never observed the slat disagree light, if the slat disagree system sensed the slats were perhaps retracted, this might account for the stall indication. Vref speed for flaps 40 degrees with slats retracted is considerably faster than normal flaps 40 degree slats fully extended. This is only a hypothetical explanation however, as we never observed the slat disagree light illuminated either in-flight or after landing.

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Original NASA ASRS Text

Title: AN MD83 ON FLARE AT 50 FT AGL HAD THE STALL WARNING AURAL, STICK SHAKER, AND STICK PUSHER ALL ACTIVATE SIMULTANEOUSLY.

Narrative: WE WERE FLYING ACR FLT XYZ FROM SEATTLE TO LOS ANGELES ON NOV/SAT/98. WE WERE CLRED FOR A VISUAL APCH TO RWY 24R AT LAX. IN THE LNDG FLARE, TRIMMED AT VREF AT APPROX 50 FT AGL, THE AURAL STALL WARNING, STICK SHAKER AND STICK PUSHER ALL ACTIVATED. AUTOTHROTTLES ON, AUTOPLT OFF. WE WERE ON A STABILIZED VISUAL APCH, 5+ MI SEPARATED BTWN US AND THE ACFT AHEAD OF US. THE ACFT THAT WE WERE FOLLOWING WAS A NON-HVY TURBOJET (EXACT TYPE UNKNOWN). WINDS WERE LIGHT AND NO RPTED WINDSHEAR IN THE AREA. THE ACFT WEIGHED 122000 LBS. WE HAD THE SPD BUGS SET USING THE V SPD REF CARD DATA FOR OUR FLAPS 40 DEGS LNDG WHICH RESULTS IN A VREF SPD OF 128 KTS. IT IS OUR AIRLINE'S STANDARD PROC TO SET THE AUTOTHROTTLE SPD REF WINDOW TO VREF +5 KTS. THE RESULTANT SPD SET IN THE AUTOTHROTTLE SPD SELECT WINDOW WAS 133 KTS. I (THE FO) WAS THE PF AND THE CAPT WAS DOING THE STANDARD PNF'S DUTIES WHICH AT THE TIME OF THE INCIDENT INCLUDED CALLING OUT AIRSPDS AND SINK RATES. SINCE THERE WAS NO WINDSHEAR RPTED, NO WAKE TURB, NO WIND GUSTS, AND NO ABNORMAL INDICATIONS OF ANY SORT IT WAS QUITE AN UNEXPECTED AND VERY SURPRISING EXPERIENCE. THE PITCH ATTITUDE WAS NORMAL, THE INDICATED AIRSPD WAS NORMAL, THE PWR SETTING WAS NORMAL AND THE AUTOTHROTTLES WERE ON. SINCE WE ARE TRAINED TO ALWAYS RESPECT STICK SHAKER IN WINDSHEAR RECOVERY AND STALL RECOVERY TRAINING, IN THE SIMULATOR, I WAS VERY RELUCTANT TO INCREASE MY PITCH ATTITUDE AS I WOULD NORMALLY DO APCHING THE LNDG FLARE PHASE OF FLT. HOWEVER, BECAUSE OF OUR VERY CLOSE PROX TO THE GND (APPROX 50 FT AGL) I WAS NOT IN A POS TO TRADE ANY PITCH ATTITUDE FOR DECREASED ANGLE OF ATTACK AS I FELT THAT THIS WOULD RESULT IN POSSIBLE AIRFRAME DAMAGE DUE TO EXCESSIVE SINK RATE. MY ONLY OTHER OPTION WAS TO ADD PWR, LOTS OF IT, ALL THE WAY TO THE MECHANICAL STOPS, WHICH I DID. WE CONTACTED THE RWY IN A FIRM LNDG AND WROTE UP THE STALL WARNING SYS IN THE MAINT LOG. I PERFORMED A THOROUGH POSTFLT INSPECTION OF THE ACFT ALONG WITH A MECH. NOTHING ABNORMAL OBSERVED. MAINT REPLACED ONE OF THE STALL WARNING COMPUTERS AND ONE OF THE AOA VANES AND INHIBITED THE STICK PUSHER SYS AND RELEASED THE ACFT TO SVC USING APPROPRIATE MEL PROCS. WHAT CAUSED THIS? I'M NOT SURE, PERHAPS THE NEXT CREW'S EXPERIENCE WILL SHED SOME LIGHT ON THE SUBJECT. THE NEXT CREW, WHILE ON APCH TO THE PUERTO VALLARTA ARPT OBSERVED A SLAT DISAGREE LIGHT WHILE ON APCH TO THE ARPT. THE SLAT DISAGREE LIGHT ILLUMINATED EARLY ENOUGH IN THE APCH TO ALLOW THE CREW TIME TO FOLLOW THE QRH PROCS FOR THE SLAT DISAGREE LIGHT ILLUMINATED PROC. THEY WERE ABLE TO LAND WITHOUT FURTHER INCIDENT AND HAVE MAINT PERFORMED ON THE ACFT. IN OUR CASE, ALTHOUGH WE NEVER OBSERVED THE SLAT DISAGREE LIGHT, IF THE SLAT DISAGREE SYS SENSED THE SLATS WERE PERHAPS RETRACTED, THIS MIGHT ACCOUNT FOR THE STALL INDICATION. VREF SPD FOR FLAPS 40 DEGS WITH SLATS RETRACTED IS CONSIDERABLY FASTER THAN NORMAL FLAPS 40 DEG SLATS FULLY EXTENDED. THIS IS ONLY A HYPOTHETICAL EXPLANATION HOWEVER, AS WE NEVER OBSERVED THE SLAT DISAGREE LIGHT ILLUMINATED EITHER INFLT OR AFTER LNDG.

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.