Aircraft equipment problem. Excessive engine vibration at altitude in icing conditions. Aircraft MD9...

Attributes
ACN	335290
Time
Date	199605
Day	Sun
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : lbb
State Reference	TX
Altitude	msl bound lower : 31000 msl bound upper : 31000
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zfw tower : atl
Operator	common carrier : air carrier
Make Model Name	MD-90 Series (DC-9-90) Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 120 flight time total : 5000 flight time type : 800
ASRS Report	335290
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 200 flight time total : 8000 flight time type : 3000
ASRS Report	335070
Events
Anomaly	aircraft equipment problem : critical inflight encounter : weather
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : overcame equipment problem flight crew : declared emergency
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

In cruise FL310, in cirrus layer with engine and wing anti- ice on with light structural icing '#2 engine vibration high' light came on. #2 vibration gauge showed 4.5-4.8 (4.0 being the limit). Complied with checklist and pulled power back to idle. Vibes guage still showed 3.5-4.5 range. Commenced drift down, reached VMC by FL280. VMC conditions did not reduce vibe indications. Diverted to lubbock, tx, for landing. Vibes reduced to normal around 12000 ft. Brought #2 up for normal 2 engine landing lbb. Callback conversation with reporter revealed the following information: reporter first officer idented aircraft as MD90 with iae V2500 engines. The aircraft was in icing conditions at the time of excessive vibrations. Flight crew followed procedures and pulled power back to idle, but the vibrations were still outside of limits until they diverted and descended out of icing conditions. Reporter has had no feedback from his company, but maintenance just placarded the vibration indicators as inoperative (maintenance carryover item -- mco). Reporter thinks that the rubber bullet nose was the source of the excessive vibration when ice was building up on it. Though, the vibration from the unsymmetrical shape is designed to shed the ice as it builds up. However, reporter thinks there was an ice accumulation before it was shed resulting in the vibration. They declared an emergency and diverted because they thought they had no use of the engine since it still had high vibration at idle power, until at lower altitude.

Original NASA ASRS Text

Title: ACFT EQUIP PROB. EXCESSIVE ENG VIBRATION AT ALT IN ICING CONDITIONS. ACFT MD90 WITH IAE2500 ENGS. ENG ANTI-ICE HEAT ONLY TO COWL. BULLET NOSE IS MADE OF RUBBER AND THAT BEING NOT SYMMETRICAL -- VIBRATES, THEORETICALLY TO SHED ICE.

Narrative: IN CRUISE FL310, IN CIRRUS LAYER WITH ENG AND WING ANTI- ICE ON WITH LIGHT STRUCTURAL ICING '#2 ENG VIBRATION HIGH' LIGHT CAME ON. #2 VIBRATION GAUGE SHOWED 4.5-4.8 (4.0 BEING THE LIMIT). COMPLIED WITH CHKLIST AND PULLED PWR BACK TO IDLE. VIBES GUAGE STILL SHOWED 3.5-4.5 RANGE. COMMENCED DRIFT DOWN, REACHED VMC BY FL280. VMC CONDITIONS DID NOT REDUCE VIBE INDICATIONS. DIVERTED TO LUBBOCK, TX, FOR LNDG. VIBES REDUCED TO NORMAL AROUND 12000 FT. BROUGHT #2 UP FOR NORMAL 2 ENG LNDG LBB. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR FO IDENTED ACFT AS MD90 WITH IAE V2500 ENGS. THE ACFT WAS IN ICING CONDITIONS AT THE TIME OF EXCESSIVE VIBRATIONS. FLC FOLLOWED PROCS AND PULLED PWR BACK TO IDLE, BUT THE VIBRATIONS WERE STILL OUTSIDE OF LIMITS UNTIL THEY DIVERTED AND DSNDED OUT OF ICING CONDITIONS. RPTR HAS HAD NO FEEDBACK FROM HIS COMPANY, BUT MAINT JUST PLACARDED THE VIBRATION INDICATORS AS INOP (MAINT CARRYOVER ITEM -- MCO). RPTR THINKS THAT THE RUBBER BULLET NOSE WAS THE SOURCE OF THE EXCESSIVE VIBRATION WHEN ICE WAS BUILDING UP ON IT. THOUGH, THE VIBRATION FROM THE UNSYMMETRICAL SHAPE IS DESIGNED TO SHED THE ICE AS IT BUILDS UP. HOWEVER, RPTR THINKS THERE WAS AN ICE ACCUMULATION BEFORE IT WAS SHED RESULTING IN THE VIBRATION. THEY DECLARED AN EMER AND DIVERTED BECAUSE THEY THOUGHT THEY HAD NO USE OF THE ENG SINCE IT STILL HAD HIGH VIBRATION AT IDLE PWR, UNTIL AT LOWER ALT.

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.

Aircraft equipment problem. Excessive engine vibration at altitude in icing conditions. Aircraft MD90 with IAE2500 engines. Engine anti-ice heat only to cowl. Bullet nose is made of rubber and that being not symmetrical -- vibrates, theoretically to shed ice.