Mdt experiences severe vibration at cruise. Descends.

Attributes
ACN	252178
Time
Date	199309
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : bvd
State Reference	IN
Altitude	msl bound lower : 13500 msl bound upper : 14000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Medium Transport, High Wing, 2 Turboprop Eng
Navigation In Use	Other Other
Flight Phase	cruise other
Route In Use	enroute airway : zid
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial
Experience	flight time last 90 days : 220 flight time total : 6000 flight time type : 270
ASRS Report	252178
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : declared emergency other
Consequence	Other Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

While in cruise we experienced severe airframe vibration. We decided that we needed to descend to a lower altitude immediately before the situation got worse. We informed the controller that we had to descend. The controller however needed to hand us off to the next controller before issuing a clearance to a lower altitude (we had our hands full and were unable to convey to him the situation fully). By the time we were issued a lower altitude we had descended through 13500 from 14000. We felt an immediate deviation was necessary so that the problem would not get worse. After descending the vibration stopped and the rest of the flight continued normally. After the situation occurred we suspected uneven propeller de-icing and informed our maintenance department. At the time of the occurrence we were operating our aircraft as per the aircraft operating manual for icing conditions.

Original NASA ASRS Text

Title: MDT EXPERIENCES SEVERE VIBRATION AT CRUISE. DSNDS.

Narrative: WHILE IN CRUISE WE EXPERIENCED SEVERE AIRFRAME VIBRATION. WE DECIDED THAT WE NEEDED TO DSND TO A LOWER ALT IMMEDIATELY BEFORE THE SIT GOT WORSE. WE INFORMED THE CTLR THAT WE HAD TO DSND. THE CTLR HOWEVER NEEDED TO HAND US OFF TO THE NEXT CTLR BEFORE ISSUING A CLRNC TO A LOWER ALT (WE HAD OUR HANDS FULL AND WERE UNABLE TO CONVEY TO HIM THE SIT FULLY). BY THE TIME WE WERE ISSUED A LOWER ALT WE HAD DSNDED THROUGH 13500 FROM 14000. WE FELT AN IMMEDIATE DEV WAS NECESSARY SO THAT THE PROB WOULD NOT GET WORSE. AFTER DSNDING THE VIBRATION STOPPED AND THE REST OF THE FLT CONTINUED NORMALLY. AFTER THE SIT OCCURRED WE SUSPECTED UNEVEN PROP DE-ICING AND INFORMED OUR MAINT DEPT. AT THE TIME OF THE OCCURRENCE WE WERE OPERATING OUR ACFT AS PER THE ACFT OPERATING MANUAL FOR ICING CONDITIONS.

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.