An air carrier DC8 freighter flight crew became concerned about a possible flap asymmetry and declared an emergency and made a reduced flap landing. Later, they found that the flap gauges displayed differential was allowed in the maintenance manual.

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Attributes
ACN	401887
Time
Date	199805
Day	Sat
Local Time Of Day	0001 To 0600
Place
Locale Reference	airport : cvg
State Reference	OH
Altitude	msl bound lower : 897 msl bound upper : 3000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : cvg tower : cvg
Operator	common carrier : air carrier
Make Model Name	DC-8 63
Operating Under FAR Part	Part 121
Flight Phase	descent : approach landing other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : cfi pilot : flight engineer
Experience	flight time last 90 days : 65 flight time total : 6250 flight time type : 660
ASRS Report	401887
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Upon flap retraction out of jfk, we had momentary asymmetric flap indications on flap position gauge. Indication corrected itself quickly, aircraft showed no rolling tendency. Consulted with company maintenance and decided to press on to destination. On approach at cvg, flaps showed 1/2 needle width asymmetry when selected to 23 degree position. Again, aircraft showed no unusual rolling tendencies, which would indicate a gauge problem. Erred to the conservative side and went back to flaps 12 degrees, ran flap asymmetry abnormal procedure. Advised ATC of situation and rolled the crash fire rescue equipment equipment as a precaution. Landed flaps 12 degrees without incident. After landing, we found out the company maintenance manuals allow up to 1/2 needle width asymmetry in normal operations. So, as far as company was concerned, we did not even have an asymmetric situation. I decided to err to the conservative side and run the procedure and roll the equipment.

Original NASA ASRS Text

Title: AN ACR DC8 FREIGHTER FLC BECAME CONCERNED ABOUT A POSSIBLE FLAP ASYMMETRY AND DECLARED AN EMER AND MADE A REDUCED FLAP LNDG. LATER, THEY FOUND THAT THE FLAP GAUGES DISPLAYED DIFFERENTIAL WAS ALLOWED IN THE MAINT MANUAL.

Narrative: UPON FLAP RETRACTION OUT OF JFK, WE HAD MOMENTARY ASYMMETRIC FLAP INDICATIONS ON FLAP POS GAUGE. INDICATION CORRECTED ITSELF QUICKLY, ACFT SHOWED NO ROLLING TENDENCY. CONSULTED WITH COMPANY MAINT AND DECIDED TO PRESS ON TO DEST. ON APCH AT CVG, FLAPS SHOWED 1/2 NEEDLE WIDTH ASYMMETRY WHEN SELECTED TO 23 DEG POS. AGAIN, ACFT SHOWED NO UNUSUAL ROLLING TENDENCIES, WHICH WOULD INDICATE A GAUGE PROB. ERRED TO THE CONSERVATIVE SIDE AND WENT BACK TO FLAPS 12 DEGS, RAN FLAP ASYMMETRY ABNORMAL PROC. ADVISED ATC OF SIT AND ROLLED THE CFR EQUIP AS A PRECAUTION. LANDED FLAPS 12 DEGS WITHOUT INCIDENT. AFTER LNDG, WE FOUND OUT THE COMPANY MAINT MANUALS ALLOW UP TO 1/2 NEEDLE WIDTH ASYMMETRY IN NORMAL OPS. SO, AS FAR AS COMPANY WAS CONCERNED, WE DID NOT EVEN HAVE AN ASYMMETRIC SIT. I DECIDED TO ERR TO THE CONSERVATIVE SIDE AND RUN THE PROC AND ROLL THE EQUIP.

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.