ROBINSON R-22 PLT HAS AN NMAC.

Narrative

I WAS IN A ROBINSON R-22; AT MIDFIELD ON THE L DOWNWIND OF RWY XXL AT 900 FT MSL; 700 FT AGL; WHEN I THOUGHT I HEARD THE TWR REQUEST I TURN AN EARLY BASE. THE L DOWNWIND IS CLOSE TO THE RWY SINCE FOR NOISE ABATEMENT PROCS WE ARE NOT ALLOWED TO FLY W OF STATE RTE; WHICH RUNS PARALLEL TO RWYS XX/YY. ATC: HELI XXX TURN EARLY BASE. XXX: EARLY BASE MIDFIELD. XXX TURNED L BASE MIDFIELD AT 900 FT; THEN TURNED FINAL OVER THE MIDDLE OF THE ACTIVE RWY XXL. I KNEW THERE WAS A LEARJET ON THE RWY AND WE DIDN'T HAVE VERY MUCH TIME TO DO THE APCH AND GET OUT OF THERE. XXX: TWR; DO YOU WANT ME TO DO A LOW APCH? ATC: LOW APCH? XXX: DO YOU WANT ME TO DO AN AUTO TO THE RWY? ATC: YES. XXX ENTERED AN AUTOROTATION AT 900 FT AND BEGAN DSNDING AT AROUND 1500 FPM OVER RWY XXL AT MIDFIELD. WHEN XXX WAS ABOUT 400 FT MSL (200 FT AGL); THE NEXT THING I KNEW A LEARJET TOOK OFF AND PASSED UNDERNEATH THE HELI ABOUT 5-10 FT AWAY. I INITIATED A PWR RECOVERY FROM THE AUTOROTATION AND BEGAN A GRADUAL FLARE; EXPECTING TO GET BOUNCED BY THE JET WASH. I WAS ABLE TO BRING THE HELI TO A SAFE HOVER 3 FT OFF THE RWY AND BEGAN TO TAKE OFF TO JOIN THE TFC PATTERN AGAIN. TWR; HELI XXX; I DIDN'T KNOW YOU'D CLRED A LEARJET TO TAKE OFF ON RWY XXL. ATC: (I DON'T REMEMBER THE FIRST THING HE SAID) DO YOU WANT TO FILE A COMPLAINT? XXX: NO. WHEN I LANDED; I RECEIVED A PHONE CALL FROM THE ATC CTLR WHO WAS WORKING WHEN THE CLOSE CALL HAPPENED. HE SAID HE NEVER TOLD ME TO TURN AN EARLY BASE. I DON'T KNOW WHERE I GOT THAT FROM; BUT I DID REPEAT IT BACK TO HIM BEFORE TURNING BASE. I THINK HE CLRED A DEPARTING HELI TO TURN EARLY XWIND AND I THOUGHT HE WAS TALKING TO ME. THEN HE SAID HE DIDN'T KNOW WHERE I WAS WHEN I ENTERED THE AUTO -- HE THOUGHT I WAS ON A NORMAL BASE; WHICH WOULD HAVE BEEN SUFFICIENT DISTANCE BEHIND THE DEPARTING LEARJET FOR ME TO ENTER AN AUTOROTATION TO THE RWY.