Altitude deviation caused by rapidly icing and badly vibrating propellers.

Attributes
ACN	301015
Time
Date	199504
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : cnx
State Reference	NM
Altitude	msl bound lower : 22000 msl bound upper : 23000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zab
Operator	other
Make Model Name	Turbo Commander 690C
Operating Under FAR Part	Part 91
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	government other
Function	flight crew : single pilot
Qualification	pilot : atp
Experience	flight time last 90 days : 35 flight time total : 18000 flight time type : 800
ASRS Report	301015
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude inflight encounter : weather non adherence : clearance non adherence : far other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : exited adverse environment flight crew : declared emergency
Consequence	faa : investigated
Supplementary
Primary Problem	Weather

Narrative:

I entered a convective situation and the aircraft experienced an extremely rapid accumulation of rime ice. The propellers iced severely causing heavy vibrations. I requested a lower altitude and was given a 45 degree turn off course. At this point, the aircraft would not sustain altitude and I descended. I feel that the dowty rotol propellers on this aircraft (aeronautical commander 690C) do not offer enough icing protection, and a serious vibration problem is apparent. When the ice departed at lower altitude, the vibration ceased. Callback conversation with reporter revealed the following information: he regrets that he did not declare an emergency, but things were not 'really bad,' even though he could not hold altitude and power. He just descended to FL220. There was an FAA investigation of the altitude deviation, but he was exonerated because of the precarious situation. The reporter is now aware of the FAA aviation safety hotline.

Original NASA ASRS Text

Title: ALTDEV CAUSED BY RAPIDLY ICING AND BADLY VIBRATING PROPS.

Narrative: I ENTERED A CONVECTIVE SIT AND THE ACFT EXPERIENCED AN EXTREMELY RAPID ACCUMULATION OF RIME ICE. THE PROPS ICED SEVERELY CAUSING HVY VIBRATIONS. I REQUESTED A LOWER ALT AND WAS GIVEN A 45 DEG TURN OFF COURSE. AT THIS POINT, THE ACFT WOULD NOT SUSTAIN ALT AND I DSNDED. I FEEL THAT THE DOWTY ROTOL PROPS ON THIS ACFT (AERO COMMANDER 690C) DO NOT OFFER ENOUGH ICING PROTECTION, AND A SERIOUS VIBRATION PROB IS APPARENT. WHEN THE ICE DEPARTED AT LOWER ALT, THE VIBRATION CEASED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: HE REGRETS THAT HE DID NOT DECLARE AN EMER, BUT THINGS WERE NOT 'REALLY BAD,' EVEN THOUGH HE COULD NOT HOLD ALT AND PWR. HE JUST DSNDED TO FL220. THERE WAS AN FAA INVESTIGATION OF THE ALTDEV, BUT HE WAS EXONERATED BECAUSE OF THE PRECARIOUS SIT. THE RPTR IS NOW AWARE OF THE FAA AVIATION SAFETY HOTLINE.

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.