A DEP B727 FLT TURNS BACK SHORTLY AFTER TKOF TO RETURN LAND AT DEN WHEN THERE IS RPTED SMOKE IN CABIN. A REQUEST FOR CFR EQUIP IS MADE AND A SHORT TURN TO LAND ON RWY 26 IS MADE AFTER FLT ATTENDANT SAYS THE CEILINGS ARE TURNING BLACK. EMER NOT DECLARED.

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ACFT HAD THE #3 HIGH/LOW STAGE PRESSURE VALVE AND PRESSURE REGULATOR REPLACED. A STATIC RUN-UP WAS DONE AND THE VALVE CHKED FINE. TAXI FOR TKOF UNEVENTFUL. FO WAS PF. TKOF UNEVENTFUL UNTIL 200-300 FT AGL. WE RECEIVED A CHIME FROM THE CABIN. WE WERE TOLD THERE WAS SMOKE IN THE CABIN. PACKS WERE OK; ENGS OK; NO OVERHEATING. CONTINUED CLB; LEVELED OFF AT 9000 FT MSL AND TOLD ATC WE WERE COMING BACK IN TO LAND BUT THAT WE NEEDED TO ASSESS THE SIT. I SENT SO BACK TO CHK THINGS OUT. HE CAME BACK AND SAID THAT THERE WAS SMOKE; IT SMELLED ELECTRICAL; BUT IT APPEARED TO BE DISSIPATING. WE DECIDED TO RETURN TO DEN AND LAND. WE WERE UNDER MAX LNDG WT. AT THIS POINT WE WERE DOWNWIND TO RWY 16 E OF THE ARPT. WE RECEIVED ANOTHER CHIME FROM THE CABIN AND WERE TOLD THAT THE CEILING PANELS 'WERE TURNING BLACK.' WE IMMEDIATELY MADE A L TURN AND HEADED FOR RWY 26 WHILE ALERTING ATC AND REQUESTING FIRE EQUIP. AT 500 FT WITH THE ACFT STABILIZED AND CHKLISTS DONE; I HAD THE SO ASK FLT ATTENDANT #1 IF WE NEEDED TO EVAC. SHE SAID NO. NOW WE WERE REALLY CONFUSED. IS THE AIRPLANE ON FIRE OR WHAT? WE LANDED; GOT OFF THE RWY AND STOPPED THE AIRPLANE. I HAD THE FLT ATTENDANT COME UP AND ASKED WHAT WAS GOING ON. SHE SAID THAT THERE DID NOT APPEAR TO BE ANY FIRE AND THE SMOKE WAS DISSIPATING. I ASKED THE FLT ATTENDANT WHO RPTED 'THE CEILING PANELS TURNING BLACK' TO COME TO THE COCKPIT. SHE SAID THAT AT THE TIME; THE CEILING PANELS DID APPEAR TO BE GETTING DARK AND STILL LOOKED A LITTLE DARK TO HER. I INSTRUCTED THE FLT ATTENDANT TO STAY IN THE AISLE (IN THE AREA OF CONCERN) WITH A FIRE EXTINGUISHER. I TOLD THE SO TO CALL COMPANY AND GET A GATE IMMEDIATELY AND TO TELL THEM WHAT WAS GOING ON. I TOLD ATC THAT WE WERE TAXIING BACK TO THE GATE BUT THAT I WANTED THE FIRE TRUCKS TO FOLLOW US. PARKING UNEVENTFUL BUT THEY WERE UNPREPARED FOR OUR ARR. THE AGENTS AND SUPVR CLAIMED THEY KNEW NOTHING ABOUT OUR ARR. PAX DISEMBARKED. WENT BACK AND LOOKED AT THE CEILING PANELS AND THEY LOOKED NORMAL. FLT DUTY MGR CALLED ME ON THE JETWAY PHONE AND I EXPLAINED THE EVENTS TO HIM. HE ASKED ME WHY I DIDN'T DECLARE AN EMER. IF ASKED BY ATC; I WOULD HAVE DONE SO; BUT AT THE TIME; I FELT THAT MY AIRPLANE WAS ON FIRE AND MY ONLY THOUGHT WAS TO GET IT ON THE GND. I DID NOT SAY THOSE WORDS (DECLARE AN EMER) BUT I THOUGHT MY MESSAGE WAS CONVEYED BY REQUESTING THE FIRE TRUCKS AND LNDG IMMEDIATELY. THIS FLT AND AIRPLANE HAD ALREADY EXPERIENCED 2 DELAYS DUE TO MECHANICAL PROBS. ONE REQUIRED THAT WE TAXI BACK TO THE GATE. THE FLT ATTENDANT THAT RPTED THE 'CEILING PANELS TURNING BLACK' HAD RECENTLY BEEN TO RECURRENT TRAINING AND HAD SEEN THE VIDEO OF THE CABIN BEING ON FIRE. I BELIEVE SHE WAS A LITTLE 'SPRING LOADED' AND GOT REALLY SCARED WHEN SHE SAW THE SMOKE. THE CEILING PANELS COVERING THE FLUORESCENT LIGHTS ARE A LITTLE OLD AND DO LOOK THAT WAY. I BELIEVE THE COMBO OF RECURRENT TRAINING; THE VIDEO; THE SMOKE; AND THE OLD CEILING PANELS CONTRIBUTED TO HER 'SEEING' THE CEILING PANELS TURNING BLACK. AS FOR MY NOT DECLARING AN EMER; I HAD THE FULL INTENTION OF DOING SO BUT IT GOT LOST IN THE HEAT OF THE BATTLE. I'M SURPRISED THAT ATC DID NOT ASK ME. I FEEL THAT THEY SHOULD HAVE. SUPPLEMENTAL INFO FROM ACN 475937: SMOKE IS BAD; HOWEVER HEARING 'CABIN CEILING TURNING BLACK' IS EVEN WORSE. AIR CONDITIONING UNIT SOMETIMES GIVES OFF A LITTLE WHITE SMOKE; BIG DIFFERENCE BTWN THAT AND CEILING TURNING BLACK.