Altitude deviation altitude excursion. Aircraft experienced extreme airframe vibration.

Attributes
ACN	252307
Time
Date	199309
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : bvt
State Reference	IN
Altitude	msl bound lower : 13500 msl bound upper : 14000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zid tower : tpa
Operator	common carrier : air carrier
Make Model Name	Medium Transport, High Wing, 2 Turboprop Eng
Navigation In Use	Other Other
Flight Phase	cruise other descent other
Route In Use	enroute airway : zid
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : cfi
Experience	flight time last 90 days : 205 flight time total : 8000 flight time type : 1000
ASRS Report	252307
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude inflight encounter other non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : exited adverse environment none taken : insufficient time
Consequence	Other
Supplementary
Primary Problem	Weather
Air Traffic Incident	Pilot Deviation

Narrative:

While in cruise we experienced extreme airframe vibration. We felt it was due to current icing conditions. We started to descend to a lower altitude before the situation worsened. We didn't receive clearance from center until we had descended through 13500 ft. We later suspected uneven propeller deicing for the cause of the vibration.

Original NASA ASRS Text

Title: ALTDEV ALT EXCURSION. ACFT EXPERIENCED EXTREME AIRFRAME VIBRATION.

Narrative: WHILE IN CRUISE WE EXPERIENCED EXTREME AIRFRAME VIBRATION. WE FELT IT WAS DUE TO CURRENT ICING CONDITIONS. WE STARTED TO DSND TO A LOWER ALT BEFORE THE SIT WORSENED. WE DIDN'T RECEIVE CLRNC FROM CTR UNTIL WE HAD DSNDED THROUGH 13500 FT. WE LATER SUSPECTED UNEVEN PROP DEICING FOR THE CAUSE OF THE VIBRATION.

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.