Narrative:

During cruise the flight deck and cabin crew detected an unrecognizable odor of which its source could not be identified. The odor would dissipate but would never completely go away. The decision was made to conduct a precautionary diversion. The divert airport's weather and proximity made it the most suitable airport for a diversion. We made the decision to wear our oxygen masks in the cockpit as a precaution against an escalating event as well as crew incapacitation can be hard to detect. I deferred the flying to our first officer because I had recently studied and reviewed both the smoke/fumes/avionics smoke checklist and the emergency descent checklist for an upcoming check ride. We did declare an emergency to give us the highest priority with ATC if an emergency descent was needed. The emergency authority would also allow us to run the smoke/fumes/avionics smoke checklist if needed as well. I notified dispatch; the passengers and flight attendants of our situation while we made our descent. While the first officer continued the descent I preformed the procedure outlined in flight operations manual. The approach and landing on the runway was routine and uneventful. We had the airport rescue and fire fighter vehicles follow us to the gate as a precaution. Once at the gate we were briefed and cleared by a member of the airport rescue and fire fighters; who informed us that they could not find any hot spots visually or through thermal imaging. The airport rescue and fire fighter officer; who was trained in smoke identification; could also not recognize the odor. Three non revenue pilots on board each described the odor differently. Maintenance control was notified and the crew was released by dispatch to continue.

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Original NASA ASRS Text

Title: The pilots and flight attendants of an A319 detected an unidentified odor while at cruise so an emergency was declared and as the SMOKE/FUMES/AVIONICS SMOKE checklist was completed the flight diverted to a nearby airport.

Narrative: During cruise the flight deck and cabin crew detected an unrecognizable odor of which its source could not be identified. The odor would dissipate but would never completely go away. The decision was made to conduct a precautionary diversion. The divert airport's weather and proximity made it the most suitable airport for a diversion. We made the decision to wear our oxygen masks in the cockpit as a precaution against an escalating event as well as crew incapacitation can be hard to detect. I deferred the flying to our First Officer because I had recently studied and reviewed both the Smoke/Fumes/Avionics Smoke Checklist and the Emergency Descent checklist for an upcoming check ride. We did declare an emergency to give us the highest priority with ATC if an emergency descent was needed. The emergency authority would also allow us to run the Smoke/Fumes/Avionics Smoke Checklist if needed as well. I notified Dispatch; the passengers and flight attendants of our situation while we made our descent. While the First Officer continued the descent I preformed the procedure outlined in Flight Operations Manual. The approach and landing on the runway was routine and uneventful. We had the Airport Rescue and Fire Fighter vehicles follow us to the gate as a precaution. Once at the gate we were briefed and cleared by a member of the Airport Rescue and Fire Fighters; who informed us that they could not find any hot spots visually or through thermal imaging. The Airport Rescue and Fire Fighter Officer; who was trained in smoke identification; could also not recognize the odor. Three non revenue pilots on board each described the odor differently. Maintenance Control was notified and the crew was released by Dispatch to continue.

Data retrieved from NASA's ASRS site as of July 2013 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.