Date: 201302
Local time of day: 1201-1800
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Daylight
Aircraft: B737-300
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Recirculation Fan
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Human factors: Physiological - Other; Training / Qualification; Time Pressure; Workload; Distraction
Second reporter function: Pilot Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Attendant; Person Flight Crew
When detected: In-flight
Result: Aircraft Equipment Problem Dissipated; Flight Crew Diverted; Flight Crew Took Evasive Action; Flight Crew FLC complied w / Automation / Advisory; General Maintenance Action; General Declared Emergency
Contributing factors: Procedure; Aircraft
Primary problem: Aircraft

Narrative: Flying at FL360 direct; the flight attendants called us and reported an acrid smell in mid-cabin. We smelled it shortly after and donned the oxygen masks. First Officer was the pilot flying so he kept aircraft control and worked the radios. The Captain worked the checklists and communicated with the flight attendants. We requested a descent from ATC while telling them of smoke in the cabin. An emergency was declared. They told us the nearest airfield so we got vectors to that field. While descending and getting vectors; the checklist was run. At the appropriate points; the flight attendants were asked if any of the smell was dissipating. They said that it seemed to be weaker. We asked if they saw smoke. They acknowledged haziness to the air. Since the smell was dissipating; when we landed; we asked the Fire Department to look from the outside and notify us if they saw any obvious problems. They didn't so we taxied to the gate and deplaned the passengers. We landed ten minutes after the first indication. Maintenance was notified. Contract Maintenance came and did the inspections. We found that the gasper fan had gone bad and had caused the smoke and odors. Upon review of the checklists; I realized that the gasper fan isn't named as a specific person's duty so I should be checking it on every flight. I have often left that to the flight attendant. Had this happened below 10;000 FT; though; it would have been even more difficult and more threats would have been added to the event. We need to either add gasper fans to the 10;000 FT Checklist or disconnect them. I will remember to check the gasper fan switch at 10;000 FT.


Second narrative: On the ground; the source of the fumes and smoke was later traced to the gasper fan. The fan was turned off as part of the QRH Smoke/Fire/Fumes on the Aircraft procedure and this certainly prevented the smoke and fumes getting worse. I normally place and leave the gasper fan in the OFF position; especially during winter time. This was our first PM (evening) leg of the day and when we left the temperature was in the 60s. I believe the gasper fan was ON when we received the aircraft and I failed to turn the gasper fan OFF either when receiving the aircraft or when climbing through 10;000 FT. My habit pattern of always turning OFF the gasper fans was used to avoid this exact issue of leaving the gasper fan on above 10;000 FT. This meant I rarely saw a gasper fan in the ON position at 10;000 FT and was a factor in my crew error. I also think winter time was a factor since these fans are rarely used.All gaspers fan should be deactivated until the problem has been fixed. Having gone through the real experience of fumes in the cabin; I think it is unacceptable to knowingly allow this condition to occur even below 10;000 FT. If these fans cannot be de-activated then I believe either the 'Before Take Off' or 'Climb' Checklist should be changed to include a check for the gasper fans in the OFF position.


Synopsis: A B737-300 Gasper Fan failed in flight and caused acrid cabin fumes; but not knowing the odors source the pilots donned oxygen; declared an emergency and diverted to a nearby airport where Maintenance discovered the cause.