A B737-300 experiencing engine vibrations was discovered to have 1 fan blade damper missing.

Attributes
ACN	469735
Time
Date	200003
Day	Sat
Local Time Of Day	0001 To 0600
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	agl single value : 0
Environment
Light	Night
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Flight Phase	ground : maintenance ground : parked
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	maintenance : technician
Qualification	technician : airframe technician : powerplant
Experience	maintenance technician : 10
ASRS Report	469735
Person 2
Affiliation	company : air carrier
Function	maintenance : technician
Qualification	technician : powerplant technician : airframe
Events
Anomaly	aircraft equipment problem : critical maintenance problem : improper maintenance non adherence : published procedure
Independent Detector	aircraft equipment other aircraft equipment : engine vibration indicator
Resolutory Action	none taken : detected after the fact
Consequence	other other
Factors
Maintenance	contributing factor : schedule pressure performance deficiency : training performance deficiency : installation performance deficiency : repair performance deficiency : testing
Supplementary
Problem Areas	Maintenance Human Performance Aircraft Chart Or Publication
Primary Problem	Maintenance Human Performance

Narrative:

Aircraft engine experienced vibration. Course of action was to lube fan blades, which we did. Apparently vibration persisted. A month later, XXX removed fan blades and found a damper with rub strip missing. They replaced damper, but vibration continued. A balance trim run was performed to bring vibrations to tolerances. I don't think the damper was the cause of the problem. I'm not familiar with how the dampers are supposed to work or even if they are supposed to have rub strips. I didn't look for missing rub strips because of this. Apparently a mechanic in XXX did know what to look for, but it still didn't solve the problem. The mechanics involved with removal of the ran blades at ZZZ didn't catch it, and the mechanic working with me on the reassembly didn't look. To this date I still don't know what I'm supposed to look for.

Original NASA ASRS Text

Title: A B737-300 EXPERIENCING ENG VIBRATIONS WAS DISCOVERED TO HAVE 1 FAN BLADE DAMPER MISSING.

Narrative: ACFT ENG EXPERIENCED VIBRATION. COURSE OF ACTION WAS TO LUBE FAN BLADES, WHICH WE DID. APPARENTLY VIBRATION PERSISTED. A MONTH LATER, XXX REMOVED FAN BLADES AND FOUND A DAMPER WITH RUB STRIP MISSING. THEY REPLACED DAMPER, BUT VIBRATION CONTINUED. A BAL TRIM RUN WAS PERFORMED TO BRING VIBRATIONS TO TOLERANCES. I DON'T THINK THE DAMPER WAS THE CAUSE OF THE PROB. I'M NOT FAMILIAR WITH HOW THE DAMPERS ARE SUPPOSED TO WORK OR EVEN IF THEY ARE SUPPOSED TO HAVE RUB STRIPS. I DIDN'T LOOK FOR MISSING RUB STRIPS BECAUSE OF THIS. APPARENTLY A MECH IN XXX DID KNOW WHAT TO LOOK FOR, BUT IT STILL DIDN'T SOLVE THE PROB. THE MECHS INVOLVED WITH REMOVAL OF THE RAN BLADES AT ZZZ DIDN'T CATCH IT, AND THE MECH WORKING WITH ME ON THE REASSEMBLY DIDN'T LOOK. TO THIS DATE I STILL DON'T KNOW WHAT I'M SUPPOSED TO LOOK FOR.

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.