ROBINSON R44 HELI PLT DSNDS TO AVOID THE WAKE TURB OF A JET DEPARTING FROM THE SJC ARPT OVER WHICH HE WAS ABOUT TO TRANSITION AT 2000 FT MSL. HE EXPERIENCED SOME TURB EVEN THOUGH HE DSNDED 500 FT AND COMPLAINS THAT ATC DOES NOT TAKE INTO CONSIDERATION THE WAKE OF OVERFLYING JETS DURING OP TO AND FROM LARGE ARPTS.

Narrative

I WAS ON A VFR FLT FROM GNOSS (DVO) TO SALINAS (SNS) VIA OAKLAND AND SAN JOSE; USING FLT FOLLOWING. AT THE TIME OF THE INCIDENT; I HAD BEEN SWITCHED TO SAN JOSE TWR FOR THE TRANSITION OF THEIR AIRSPACE; AND GIVEN A CLRNC 'TO CROSS MIDFIELD AT OR ABOVE 2000 FT.' I CONTINUED ON THE SAME HDG TOWARDS THE FIELD. HOWEVER; A JET ACFT TAKING OFF TURNED DIRECTLY TOWARDS ME AND WOULD PASS CLOSE ENOUGH OVERHEAD TO MAKE ME VERY CONCERNED ABOUT WAKE TURB. SO I TOOK EVASIVE ACTION BY USING AFT CYCLIC AND LOWERED THE COLLECTIVE TO REDUCE THE HELI TO MANEUVERING SPD. I LOST ABOUT 500 FT IN ALT. THERE WAS NO TIME TO GET PERMISSION TO TAKE ACTION WITH THE BUSY RADIO TFC. SHORTLY AFTERWARDS; A DIFFERENT CTLR SAID THAT 'I HAD BEEN GIVEN A CLRNC TO MAINTAIN VFR AND CROSS MIDFIELD AT OR ABOVE 2000 FT.' AND I 'HAD DSNDED INTO THE APCH PATH.' I REPLIED THAT 'I NEEDED TO TAKE EVASIVE ACTION TO AVOID THE WAKE TURB.' (NEVERTHELESS; I STILL RECEIVED A STRONG JOLT OF TURB.) ALSO IT WAS MY UNDERSTANDING THAT I WAS CLRED TO 'CROSS MIDFIELD AT OR ABOVE 2000 FT;' NOT 'TO MAINTAIN 2000 FT OR ABOVE AND CROSS MIDFIELD.' THE WORDING OF THE CLRNC IS CONFUSING AS TO THE ALT REQUIREMENT IMMEDIATELY PRIOR TO REACHING MIDFIELD. MORE WORRYING; IS THAT CTLRS GIVE THE USUAL WARNING ABOUT WAKE TURB TO DEPARTING ACFT BUT DO NOT SEEM TO BE CONCERNED ABOUT TURB FROM OVERFLT OF TRANSITIONING ACFT. I EXPERIENCED EXTREME TURB AT SFO WHEN A HVY SLOW JET WAS ALLOWED TO TAKE OFF RIGHT OVER ME WHILE TRANSITIONING THEIR AIRSPACE ON A PREVIOUS OCCASION. (BANGED MY HEAD ON THE CEILING!)