Narrative:

We were cleared for an ILS runway 4 lga, circle to land runway 31. WX was approximately 1200 ft overcast, winds 310/25 gusts 35, light to moderate turbulence. We added 20 KTS to our final approach speed. At approximately 150 ft on short final to runway 31, our airspeed increased by 15-20 KTS. We landed and made a PIREP to the lga tower. They issued a warning to the next aircraft. He landed and reported a windshear on short final. He said he was too busy to figure out exactly what happened. As you know, lga runway 31 has a dike that is shaped like a ramp at the approach end. Since I have experienced this phenomenon several times to a lesser degree on this same runway, I thought I would write it up. My theory is that a wind straight down runway 31 hits that ramp shaped dike and rises causing aircraft to be forced upwards. This causes the aircraft to rise necessitating nose down action increasing airspeed on short final. If you have other reports of this phenomenon, perhaps a warning of some sort should be in the commercial approach plates. Also, next time strong winds from 310 degrees exist, perhaps a small smoke generator or a small balloon being released might confirm this wind.

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Original NASA ASRS Text

Title: AN ACR LGT CAPT ATTRIBUTES HIS SINKING FEELING TO THE DIKE AT THE END OF LGA RWY 31. THERE WERE VERY BIG WINDS ABOUT THIS NIGHT.

Narrative: WE WERE CLRED FOR AN ILS RWY 4 LGA, CIRCLE TO LAND RWY 31. WX WAS APPROX 1200 FT OVCST, WINDS 310/25 GUSTS 35, LIGHT TO MODERATE TURB. WE ADDED 20 KTS TO OUR FINAL APCH SPD. AT APPROX 150 FT ON SHORT FINAL TO RWY 31, OUR AIRSPD INCREASED BY 15-20 KTS. WE LANDED AND MADE A PIREP TO THE LGA TWR. THEY ISSUED A WARNING TO THE NEXT ACFT. HE LANDED AND RPTED A WINDSHEAR ON SHORT FINAL. HE SAID HE WAS TOO BUSY TO FIGURE OUT EXACTLY WHAT HAPPENED. AS YOU KNOW, LGA RWY 31 HAS A DIKE THAT IS SHAPED LIKE A RAMP AT THE APCH END. SINCE I HAVE EXPERIENCED THIS PHENOMENON SEVERAL TIMES TO A LESSER DEG ON THIS SAME RWY, I THOUGHT I WOULD WRITE IT UP. MY THEORY IS THAT A WIND STRAIGHT DOWN RWY 31 HITS THAT RAMP SHAPED DIKE AND RISES CAUSING ACFT TO BE FORCED UPWARDS. THIS CAUSES THE ACFT TO RISE NECESSITATING NOSE DOWN ACTION INCREASING AIRSPD ON SHORT FINAL. IF YOU HAVE OTHER RPTS OF THIS PHENOMENON, PERHAPS A WARNING OF SOME SORT SHOULD BE IN THE COMMERCIAL APCH PLATES. ALSO, NEXT TIME STRONG WINDS FROM 310 DEGS EXIST, PERHAPS A SMALL SMOKE GENERATOR OR A SMALL BALLOON BEING RELEASED MIGHT CONFIRM THIS WIND.

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.