Narrative:

While level at 7000' approaching gonne intersection, there became a noticeable burning odor coming from what the flight crew believed was the air conditioning system. As per the aircraft quick reference handbook (QRH) we turned off the right pack trying to isolate the source. The odor appeared to stabilize, but after a few mins the smell was noticeable again so the other pack was then isolated. We asked the flight attendant if there was any odor or smoke in the passenger cabin. He replied 'no' and was instructed to keep us apprised. We also visually checked the cabin 2-3 times within the next 10 mins, there was no smoke. While being vectored on the downwind, approximately 15 mi from runway 23L at cle the odor suddenly became very strong. At this time we requested no delays and advised ATC of our condition. Immediately the controller vectored us 180 degree to intercept the 23L localizer. We advised the F/a to prepare the cabin for a possible evacuate/evacuation, and requested the fire trucks as a precaution. The air conditioning, fans, and bleeds were closed and we landed uneventfully. Once clear of the runway we asked that the fire crew check the outside of the aircraft for fire or smoke damage. The odor inside the cockpit had subsided. When they reported all was okay, we taxied to the gate and deplaned, with the fire trucks surrounding the aircraft. At no time during any phase of the flight were there any indications of a malfunction. All systems were functioning normally. There were no warning lights, or any indication of a system fault. Callback conversation with reporter revealed the following: we conferred with the cabin attendant several times to see if odor was penetrating the cabin and it was not. But odor kept getting stronger in the cockpit. Post-flight inspection revealed that the left panel of the windshield was shorting out when we used windshield heat. We had windshield icing that day and apparently as we got lower into warmer outside temperatures the windshield got hotter and the shorting caused more odor.

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Original NASA ASRS Text

Title: BURNING ODOR IN COCKPIT CAUSED FLT CREW TO DECLARE EMERGENCY FOR IMMEDIATE LNDG.

Narrative: WHILE LEVEL AT 7000' APCHING GONNE INTXN, THERE BECAME A NOTICEABLE BURNING ODOR COMING FROM WHAT THE FLT CREW BELIEVED WAS THE AIR CONDITIONING SYSTEM. AS PER THE ACFT QUICK REFERENCE HANDBOOK (QRH) WE TURNED OFF THE RIGHT PACK TRYING TO ISOLATE THE SOURCE. THE ODOR APPEARED TO STABILIZE, BUT AFTER A FEW MINS THE SMELL WAS NOTICEABLE AGAIN SO THE OTHER PACK WAS THEN ISOLATED. WE ASKED THE FLT ATTENDANT IF THERE WAS ANY ODOR OR SMOKE IN THE PAX CABIN. HE REPLIED 'NO' AND WAS INSTRUCTED TO KEEP US APPRISED. WE ALSO VISUALLY CHECKED THE CABIN 2-3 TIMES WITHIN THE NEXT 10 MINS, THERE WAS NO SMOKE. WHILE BEING VECTORED ON THE DOWNWIND, APPROX 15 MI FROM RWY 23L AT CLE THE ODOR SUDDENLY BECAME VERY STRONG. AT THIS TIME WE REQUESTED NO DELAYS AND ADVISED ATC OF OUR CONDITION. IMMEDIATELY THE CTLR VECTORED US 180 DEG TO INTERCEPT THE 23L LOC. WE ADVISED THE F/A TO PREPARE THE CABIN FOR A POSSIBLE EVAC, AND REQUESTED THE FIRE TRUCKS AS A PRECAUTION. THE AIR CONDITIONING, FANS, AND BLEEDS WERE CLOSED AND WE LANDED UNEVENTFULLY. ONCE CLEAR OF THE RWY WE ASKED THAT THE FIRE CREW CHECK THE OUTSIDE OF THE ACFT FOR FIRE OR SMOKE DAMAGE. THE ODOR INSIDE THE COCKPIT HAD SUBSIDED. WHEN THEY REPORTED ALL WAS OKAY, WE TAXIED TO THE GATE AND DEPLANED, WITH THE FIRE TRUCKS SURROUNDING THE ACFT. AT NO TIME DURING ANY PHASE OF THE FLT WERE THERE ANY INDICATIONS OF A MALFUNCTION. ALL SYSTEMS WERE FUNCTIONING NORMALLY. THERE WERE NO WARNING LIGHTS, OR ANY INDICATION OF A SYSTEM FAULT. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING: WE CONFERRED WITH THE CABIN ATTENDANT SEVERAL TIMES TO SEE IF ODOR WAS PENETRATING THE CABIN AND IT WAS NOT. BUT ODOR KEPT GETTING STRONGER IN THE COCKPIT. POST-FLT INSPECTION REVEALED THAT THE LEFT PANEL OF THE WINDSHIELD WAS SHORTING OUT WHEN WE USED WINDSHIELD HEAT. WE HAD WINDSHIELD ICING THAT DAY AND APPARENTLY AS WE GOT LOWER INTO WARMER OUTSIDE TEMPERATURES THE WINDSHIELD GOT HOTTER AND THE SHORTING CAUSED MORE ODOR.

Data retrieved from NASA's ASRS site as of August 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.