A HELICOPTER AIR AMBULANCE DESCENDED AND STRUCK THE GND IN VMC WITH LIGHT FOG. NO DAMAGE TO ACFT BUT THE PILOT DID NOT HEAR ALERTING RADIO ALTIMETER.

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UPON DEP FROM HOSPITAL AT XA52 LCL TIME; I ENCOUNTERED SOME VERY THIN SCATTERED LAYERS OF FORMING FOG AT APPROX 300 FT AGL. I COULD MAINTAIN VISUAL CONTACT WITH LIGHTS AHEAD OF MY HELI AND OFF TO THE R FRONT SEVERAL MI AWAY. WHILE MANEUVERING TO REMAIN CLR OF THE FORMING FOG LAYERS; I INADVERTENTLY LET THE ACFT DSND AND CONTACTED SOFT GND RESULTING IN DAMAGE TO THE R SIDE SKID LIGHTS ON THE AFT CROSS TUBE. AT THE TIME OF THE INCIDENT; I INITIALLY THOUGHT THAT I HAD HAD A BIRD STRIKE SINCE ALL I SAW WAS A WHITE FLASH AND FELT A THUMP AND THOUGHT THAT I WAS STILL AT 300 FT. THE RADAR ALTIMETER WAS SET TO ALARM WHEN DSNDING BELOW 200 FT. I DO NOT RECALL HEARING THE WARNING SOUND FROM IT. NO OTHER DAMAGE TO THE ACFT WAS NOTED UPON POSTFLT INSPECTION. THERE WAS NO PRESSURE TO TAKE THIS FLT FROM THE HOSPITAL OR MY PEERS. THE WX WAS ABOVE MINIMUMS FOR OUR OP AND WAS FORECAST TO REMAIN SO FOR THE DURATION OF THE FLT. THE FOG FORMING WAS NOT EXPECTED UNTIL AFTER XC00 HRS; BUT THIS FOG BEGAN FORMING SEVERAL HRS EARLIER THAN EXPECTED. RAIN SHOWERS AND TSTMS ALSO FORMED THAT WERE NOT FORECAST; HOWEVER; THEY WERE NOT A CONTRIBUTING FACTOR TO THIS INCIDENT.