INST RATED PVT PLT BECAME DISORIENTED DURING A XCOUNTRY FLT WHEN FLYING OVER AN UNDERCAST AS IT BECAME DARK. AFTER CONTACTING APCH CTL; ATC PROVIDED A FLT ASSIST AND GAVE HIM NO GYRO VECTORS TO DEST SINCE HIS VACUUM SYS HAD FAILED. HE ALSO LEARNED THAT HE HAD ENTERED CLASS B AIRSPACE OVER THE LAX MARKER BEACONS.

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I WAS RETURNING FROM SACRAMENTO ON A XCOUNTRY FLT GOING BACK TO LONG BEACH. THE WX HAD BEEN FINE ALL THROUGHOUT THE TRIP. IT WAS THEN ABOUT XA00 AND GETTING DUSKY WHEN I WAS CLOSE TO VAN NUYS. THE SOCAL APCH CTLR TOLD ME TO STAY W OF THE VNY ARPT; WHICH I HAD STAYED WELL CLR OF IT. I WAS GETTING FLT FOLLOWING THROUGHOUT THE ENTIRE TRIP. A FEW MINS LATER; THE CTLR TOLD ME TO SQUAWK VFR AND THAT RADAR SVCS WERE TERMINATED. I WAS THEN RIGHT OVER A MOUNTAIN RANGE CRUISING AT 3500 FT; HOMING IN TO SMO VOR. I WAS GOING TO TAKE THE SMO 312 DEG RADIAL SPECIAL FLT RULES AREA TO PASS THROUGH THE LAX CORRIDOR; WHICH I HAD DONE NUMEROUS TIMES BEFORE. UPON REACHING THE MOUNTAIN PASS; I SAW A MARINE LAYER COVERING THE GND AND WATER AS FAR AS I COULD SEE. I WAS TRYING TO TRACK THE SMO 312 DEG RADIAL AND THEN A LARGE JET WAS APCHING MY WAY TO LAND AT VNY ARPT. I TURNED AND MADE A QUICK DSCNT TO GET OUT OF ITS PATH. AFTER IT HAD PASSED; I TURNED AND CLBED BACK UP TO 3500 FT TO CONTINUE TRACKING THE SMO 312 DEG RADIAL. THEN; I FOUND MYSELF OFF COURSE AND COULDN'T SEE ANYTHING BELOW ME. I HAD NO IDEA IF I WAS OVER LAND OR WATER. I SAW A FEW OTHER PLANES FLYING IN THE VICINITY OF LAX. DUE TO THE MARINE LAYER; I COULDN'T SEE LAX; BUT I KNEW IT WAS SEVERAL MI AWAY. I THOUGHT IT WOULD BE THE BEST IDEA TO CONTACT SOCAL AGAIN AND GET A CLRNC THROUGH THE CLASS B AIRSPACE; AND ALSO MAKE AN ILS APCH INTO LGB. SINCE I COULDN'T SEE WHAT WAS BELOW ME FOR GND REF; I WASN'T SURE IF I WAS ALREADY IN CLASS B AIRSPACE OR NOT. I DIDN'T THINK THAT I WAS. AFTER CONTACTING SOCAL; I WAS CLRED THROUGH THE AREA AND RADAR VECTORED TO LGB. I WAS FLYING A NO-GYRO APCH AS THE AIRPLANE'S VACUUM SYS WENT OUT DURING FLT. I HAD TO RELY HEAVILY ON THE MAGNETIC COMPASS FOR NAV. I THOUGHT I DID WHAT WAS FEASIBLE AND NECESSARY UNDER THE CONDITIONS I WAS UNDER. IT WAS THEN ON THE DOWNWIND LEG OF THE APCH THAT I WAS INSTRUCTED BY SOCAL TO CALL A SOCAL SUPVR REGARDING ENTRANCE INTO CLASS B AIRSPACE. WITHIN 30 MINS OF LNDG; I CALLED THE SOCAL SUPVR AND GAVE HIM MY INFO AND EXPLAINED WHAT HAD HAPPENED. HE SAID THAT I WAS IN CLASS B AIRSPACE RIGHT OVER THE MARKER BEACONS OF LAX AND THAT IT WAS IN ABOUT THE WORSE AREA TO BE IN. I CAN'T CONFIRM THAT; AS I COULDN'T SEE ANYTHING DOWN BELOW. THAT WAS THE REASON WHY I CONTACTED SOCAL INITIALLY. HE THEN SAID I'LL BE CONTACTED BY FSDO IN A COUPLE OF WKS. ALL I CAN DO NOW IS WAIT.