CLOSE PROX ACR-MLG; 2 SPN'S AND A HANG GLIDER WHILE ON VECTOR APCH FROM OVER OAKLAND HILLS.

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PLEASE COUNT THIS AS 3 SEPARATE NMAC'S. WE WERE ON A WESTERLY HDG TO INTERCEPT THE OAK 29 LOC; LEVEL 4000'. I NOTICED WHAT APPEARED TO BE A LIGHT ACFT A COUPLE OF MILES AHEAD. AS I WAS WATCHING IT; I SPOTTED A GLIDER AT 11 O'CLOCK; OUR ALT; CLOSE IN; SAME DIRECTION. THE GLIDER PASSED OFF OUR LEFT; APPROX 100-200' AWAY; AT OUR ALT. THE COPLT KEPT WATCHING THAT GLIDER AND DSNDED TO 3800'; WHEN HE NOTICED THE GLIDER TURN TOWARD US AS WE PASSED. I LOOKED AHEAD TO SEE WHAT HAPPENED TO THE ORIGINAL TFC; WHICH TURNED OUT NOT TO BE AN AIRPLANE 2 MI AWAY; BUT A HANG GLIDER A FEW HUNDRED FT AWAY. IT ALSO PASSED US 100-200' TO OUR LEFT; AT OUR ALT. I LOOKED AHEAD AGAIN AND SAW A SECOND GLIDER DEAD AHEAD; OUR ALT. I SAID; 'PULL UP;' WHICH THE COPLT DID; AND WE CLRED THE GLIDER BY APPROX 100'. BAY APCH SAID THEY HAD NO RADAR CONTACT. MY SUGGESTION FOR ALLEVIATING THESE INCIDENTS IS: REQUIRE ALT ENCODERS IN HIGH DENSITY AIRSPACE. WE ARE DEFINITELY GOING TO HAVE MORE MIDAIR COLLISIONS INVOLVING AIRLINERS UNTIL SOMETHING IS DONE. SEE AND AVOID IS NOT ACCEPTABLE!