B737-300 crew had suspected engine fan blade icing that was detected on the vibration monitor.

Attributes
ACN	564536
Time
Date	200210
Day	Thu
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : den.airport
State Reference	CO
Altitude	agl single value : 0
Environment
Weather Elements	Ice Fog
Aircraft 1
Controlling Facilities	tower : atl.tower
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Flight Phase	ground other : eng runup
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	564536
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : less severe inflight encounter : weather inflight encounter other other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : vibration monitor other flight crewa other flight crewb
Resolutory Action	other
Consequence	other other
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft Weather
Primary Problem	Aircraft

Narrative:

WX was IFR, temperature 18 degrees F, visibility 1 mi. After remote deiced, took runway 34 for takeoff. Performed engine runup on runway. Noticed initially #2 engine vibration higher than normal (3.0). After a few seconds, returned to more normal value (1.5). All other engine parameters completely normal. After runup, commenced takeoff and everything was normal until 10000 ft. #2 engine went above 4.0 on vibration. I suspected engine ice and performed ice shedding procedure (45% then to 80%) and ran high vibration irregular procedure for engine ice. Engine immediately returned to normal value (1.5). We continued to cruise and engine was normal until descent. On descent to phl, whenever engine thrust changed (retarded or advanced), vibration would go initially to around 3.0, then return again to 1.5 or so. Now wondered if we had something more than an ice problem, as no icing conditions existed into phl. Made a log entry and discussed with maintenance on arrival. Next day, found out engine had rotor blade warping. I believe we did everything correctly. Maybe should have retarded throttles to idle on runup and tried runup second time, but at time, did not seem necessary as engine vibration returned to normal value during runup.

Original NASA ASRS Text

Title: B737-300 CREW HAD SUSPECTED ENG FAN BLADE ICING THAT WAS DETECTED ON THE VIBRATION MONITOR.

Narrative: WX WAS IFR, TEMP 18 DEGS F, VISIBILITY 1 MI. AFTER REMOTE DEICED, TOOK RWY 34 FOR TKOF. PERFORMED ENG RUNUP ON RWY. NOTICED INITIALLY #2 ENG VIBRATION HIGHER THAN NORMAL (3.0). AFTER A FEW SECONDS, RETURNED TO MORE NORMAL VALUE (1.5). ALL OTHER ENG PARAMETERS COMPLETELY NORMAL. AFTER RUNUP, COMMENCED TKOF AND EVERYTHING WAS NORMAL UNTIL 10000 FT. #2 ENG WENT ABOVE 4.0 ON VIBRATION. I SUSPECTED ENG ICE AND PERFORMED ICE SHEDDING PROC (45% THEN TO 80%) AND RAN HIGH VIBRATION IRREGULAR PROC FOR ENG ICE. ENG IMMEDIATELY RETURNED TO NORMAL VALUE (1.5). WE CONTINUED TO CRUISE AND ENG WAS NORMAL UNTIL DSCNT. ON DSCNT TO PHL, WHENEVER ENG THRUST CHANGED (RETARDED OR ADVANCED), VIBRATION WOULD GO INITIALLY TO AROUND 3.0, THEN RETURN AGAIN TO 1.5 OR SO. NOW WONDERED IF WE HAD SOMETHING MORE THAN AN ICE PROB, AS NO ICING CONDITIONS EXISTED INTO PHL. MADE A LOG ENTRY AND DISCUSSED WITH MAINT ON ARR. NEXT DAY, FOUND OUT ENG HAD ROTOR BLADE WARPING. I BELIEVE WE DID EVERYTHING CORRECTLY. MAYBE SHOULD HAVE RETARDED THROTTLES TO IDLE ON RUNUP AND TRIED RUNUP SECOND TIME, BUT AT TIME, DID NOT SEEM NECESSARY AS ENG VIBRATION RETURNED TO NORMAL VALUE DURING RUNUP.

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.