DC9 HAS SMOKE IN CABIN ON APCH TO MSP. EMER DECLARED AND APCH EXPEDITED. OIL FOUND IN ENG COWLING AFTER LNDG.

Narrative

LEAD FLT ATTENDANT CAME INTO THE COCKPIT AND SAID THAT THE L REAR LAVATORY SMOKE DETECTOR WAS ACTIVATED AND THAT THERE WAS NO INDICATION OF HEAT OR EVIDENCE THAT SOMEONE HAD BEEN SMOKING IN THE LAVATORY. I SPED UP THE ACFT TO THE MAX ALLOWABLE SPD. A FEW MINS LATER; SHE CAME BACK TO THE COCKPIT AND SAID THERE MAY BE A BLUISH/GRAY HAZE IN THE CABIN. SHE CAME BACK IN APPROX 1 MIN LATER AND SAID THAT THE FIRST CLASS LAVATORY (UP FRONT) SMOKE DETECTOR WAS ALSO GOING OFF. BY THIS TIME WE HAD DECLARED AN EMER AND REQUESTED A STRAIGHT-IN APCH TO RWY 12L AT MSP; WHICH WAS THE CLOSEST RWY TO OUR ACFT. WE DONNED OUR OXYGEN MASKS AND THE FLT ATTENDANTS PREPARED THE CABIN FOR A POSSIBLE GND EVAC. WE ALSO TESTED THE CARGO COMPARTMENT SMOKE DETECTOR SYS TO ENSURE IT WAS WORKING PROPERLY. AFTER LNDG; WE CLRED THE RWY AND STOPPED IMMEDIATELY. WE HAD THE FIRE DEPT MEET US AND CHK THE ACFT EXTERIOR AND BOTH CARGO COMPARTMENTS. THEY SAID THAT EVERYTHING LOOKED GOOD AND WE THEN TAXIED TO THE GATE. WE ALSO PUT RAM AIR ON TO ALLOW FRESH AIR INTO CABIN (AS SOON AS WE CLRED THE RWY). DURING THE ENTIRE SIT; WE DID NOT HAVE ANY UNUSUAL INDICATIONS IN THE COCKPIT EXCEPT THE L ENG OIL QUANTITY GAUGE SHOWED THAT IT HAD DROPPED TO 4 QUARTS FROM 9-10 QUARTS IN JUST OVER AN HR OF FLT. WHEN MAINT OPENED THE L ENG NACELLE; THEY FOUND OIL ALL OVER THE INSIDE OF THE COWLING. SUPPLEMENTAL INFO FROM ACN 463206: WITH OXYGEN MASK ON; IT IS VERY HARD TO COMMUNICATE WITH THE OTHER PLT; SO I TOOK CTL OF THE PLANE AND TOLD COPLT TO DO CHKLISTS. LESSONS LEARNED: 1) VERY HARD TO COMMUNICATE WITH OXYGEN MASK ON; AND WITH DC9'S WITH OLD STYLE COM PANEL; COM WITH FLT ATTENDANTS AND PAX ALMOST IMPOSSIBLE. (PROCS TELL US TO HOLD PA HANDSET TO THROAT.) 2) IT IS VERY USEFUL TO HAVE FIRE DEPT ON GND FREQ OR SEPARATE PUBLISHED FREQ; BUT FOR SOME REASON THE FIRE CHIEF WAS SLOW TO RESPOND TO MY COMS. 3) NEVER FOUND SOURCE OF SMOKE. AFTER LNDG; I NOTICED L ENG HAD CONSUMED 4 QUARTS OF OIL. MECHS SAID THERE WAS NO WAY THAT OIL COULD HAVE GOTTEN IN CABIN.