Aircraft equipment problem recirculation fan 'ate itself up.'

Attributes
ACN	314939
Time
Date	199509
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : rzc airport : fsm
State Reference	AR
Altitude	msl bound lower : 19000 msl bound upper : 19000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zfw
Operator	common carrier : air carrier
Make Model Name	ATR 72
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other other other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : cfi
Experience	flight time last 90 days : 150 flight time total : 7000 flight time type : 600
ASRS Report	314939
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	other other : unspecified
Resolutory Action	flight crew : declared emergency other
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

While cruising at FL190, flight attendant reported 'high pitch squeal' on top of the cabin at seat row 13. First officer was sent back to investigate. Upon return, he described noise as a 'pump about to burn itself up.' all cockpit indications were normal -- we tried turning off recirculation fans and adjusting cockpit temperatures (ice in ducts) in order to stop the noise to no avail. Noise was reported coming from on top of the cabin where no pumps exist. We reviewed checklists and aircraft operating manual to see if a solution could be found. During this time, attendant came to the cockpit and said that a 'heavy electrical smoke smell was in the cabin.' we declared an emergency and diverted to ft smith. Smell was unnoticeable in the cockpit. After an uneventful approach and landing, aircraft was taxied to the terminal. Flight attendants were briefed to prepare for an emergency evacuate/evacuation and to notify me immediately of any change in conditions in back (ie, visible smoke or flame). After passenger disembarked aircraft, fire and rescue came aboard aircraft. They could also smell the electrical smell, but could not locate the source. Callback conversation with reporter revealed the following information: the reporter flies the AT72 for an air carrier. A recirculation fan in the overhead compartment 'ate itself up' producing the electrical smoke. The passenger were disembarked normally at the terminal.

Original NASA ASRS Text

Title: ACFT EQUIP PROB RECIRCULATION FAN 'ATE ITSELF UP.'

Narrative: WHILE CRUISING AT FL190, FLT ATTENDANT RPTED 'HIGH PITCH SQUEAL' ON TOP OF THE CABIN AT SEAT ROW 13. FO WAS SENT BACK TO INVESTIGATE. UPON RETURN, HE DESCRIBED NOISE AS A 'PUMP ABOUT TO BURN ITSELF UP.' ALL COCKPIT INDICATIONS WERE NORMAL -- WE TRIED TURNING OFF RECIRCULATION FANS AND ADJUSTING COCKPIT TEMPS (ICE IN DUCTS) IN ORDER TO STOP THE NOISE TO NO AVAIL. NOISE WAS RPTED COMING FROM ON TOP OF THE CABIN WHERE NO PUMPS EXIST. WE REVIEWED CHKLISTS AND ACFT OPERATING MANUAL TO SEE IF A SOLUTION COULD BE FOUND. DURING THIS TIME, ATTENDANT CAME TO THE COCKPIT AND SAID THAT A 'HVY ELECTRICAL SMOKE SMELL WAS IN THE CABIN.' WE DECLARED AN EMER AND DIVERTED TO FT SMITH. SMELL WAS UNNOTICEABLE IN THE COCKPIT. AFTER AN UNEVENTFUL APCH AND LNDG, ACFT WAS TAXIED TO THE TERMINAL. FLT ATTENDANTS WERE BRIEFED TO PREPARE FOR AN EMER EVAC AND TO NOTIFY ME IMMEDIATELY OF ANY CHANGE IN CONDITIONS IN BACK (IE, VISIBLE SMOKE OR FLAME). AFTER PAX DISEMBARKED ACFT, FIRE AND RESCUE CAME ABOARD ACFT. THEY COULD ALSO SMELL THE ELECTRICAL SMELL, BUT COULD NOT LOCATE THE SOURCE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR FLIES THE AT72 FOR AN ACR. A RECIRCULATION FAN IN THE OVERHEAD COMPARTMENT 'ATE ITSELF UP' PRODUCING THE ELECTRICAL SMOKE. THE PAX WERE DISEMBARKED NORMALLY AT THE TERMINAL.

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