CREW HAD BURNING ODOR PRESENT IN THE COCKPIT.

Narrative

DURING CRUISE FLT AT APPROX XA00Z; THE FO REMARKED WITH SOME CONCERN THAT HE SMELLED A STRONG BURNING ODOR AND ASKED IF I DETECTED ANY SUCH ODOR. I STATED AFTER 10-15 SECONDS THAT I DID AS WELL. A FLT ATTENDANT IN THE COCKPIT VERIFIED HER AWARENESS AS THE ODOR INCREASED. I DISPATCHED THE FLT ATTENDANT TO ASSESS GALLEY/CABIN CONDITIONS WHILE THE FO AND I ASSESSED COCKPIT/SYS PERFORMANCE. NO VISIBLE SMOKE WAS PRESENT; HOWEVER; ODOR INCREASED TO THE POINT THAT BOTH PLTS DONNED MASKS/GOGGLES AS QUICK REF CHKLISTS WERE ACCOMPLISHED. AS BOTH PLTS WERE UNABLE TO LOCATE SOURCE; A PRECAUTIONARY LNDG WAS ELECTED AT FSD. A 'CABIN ALERT' WAS DECLARED. NO EMER WAS DECLARED AND CFR EQUIP WAS REQUESTED. A NORMAL APCH AND LNDG WERE MADE AND PAX REMAINED CALM. A THOROUGH TROUBLESHOOTING BY MAINT REVEALED A PARTIALLY (50%) BLOCKED FO FMC/CDU INLET COOLING FILTER. MECH STATED THIS 'COULD EASILY HAVE CAUSED AN OVERHEAT WITH THE ACCOMPANYING ODOR. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: CREW WAS FLYING A B757-200. RPTR SUBMITTED A COMPANY RPT SUGGESTING THAT FILTER MAINT SCHEDULE BE INCREASED. HE HAS HEARD NOTHING FROM THE COMPANY.