SMOKE IN THE COCKPIT ON AN ACR MD80.

Narrative

DURING LAST PHASE OF CLBOUT; FL270 FOR FL280; SMOKE STARTED 'FLOWING' FROM FO'S RUDDER WELL AREA. HAD TO USE OXYGEN MASKS. DECLARED AN EMER AND RETURNED TO PHL. SMOKE DISSIPATED DURING DSCNT. ON LNDG; RETURNED TO GATE AND PAX DEPLANED NORMALLY. LNDG WAS OVERWT; 140000 LBS (MAX 128000 LBS). TOTAL PAX = 139. MAINT INDICATED THERE WAS A MOTOR (POSSIBLY SPD BRAKE?) UNDER THE CTR PEDESTAL THAT BURNED UP AND WAS TOO HOT TO TOUCH. FO AND CAPT EXPERIENCED BURNING OF EYES AND LUNGS FROM SMOKE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR SAID THE SMOKE WAS FOUND TO BE COMING FROM THE SPD BRAKE ACTUATOR MOTOR THAT IS LOCATED BELOW THE COCKPIT PEDESTAL. NO CIRCUIT BREAKERS POPPED. THE SMOKE WAS AT FIRST THOUGHT TO BE AN ODOR FROM THE CABIN. IT WAS NOT RECOGNIZED AS THE TYPICAL ELECTRICAL FIRE SMELL. IT WAS NOT VISIBLE BECAUSE OF REDUCED LIGHTING DURING THE NIGHT FLT. WHEN LIGHTS WERE TURNED UP; THE COCKPIT WAS FILLED WITH A HAZE OF SMOKE; OXYGEN MASKS WERE USED; BUT TOXICOLOGY TESTS WERE RUN ON THE CREW SINCE THERE WAS SOME DELAY IN THEIR USE. NO NEGATIVE PROBS WERE APPARENT.