GA small aircraft unable to clear carburetor ice declared an emergency and diverted to alternate.

Attributes
ACN	138441
Time
Date	199002
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : bdl
State Reference	CT
Altitude	msl bound lower : 0 msl bound upper : 7000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : bdl
Operator	general aviation : personal
Make Model Name	Small Aircraft, Low Wing, 1 Eng, Retractable Gear
Flight Phase	cruise other descent other
Route In Use	enroute : on vectors enroute : direct
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : private pilot : instrument
Experience	flight time last 90 days : 47 flight time total : 800
ASRS Report	138441
Person 2
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Events
Anomaly	aircraft equipment problem : critical inflight encounter : weather
Independent Detector	other flight crewa
Resolutory Action	aircraft : equipment problem dissipated controller : provided flight assist flight crew : declared emergency none taken : anomaly accepted
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance

Narrative:

Departed teb, VFR to bvy, having obtained WX from the ivrs system, satisfied that VFR flight was possible. Over the hudson river, 20 mi ssw of pdu, saw snow showers ahead and contacted pdu tower for an ARTCC frequency to request an IFR clearance. Obtained prompt clearance to 7000'. At about 15 mi east of bdl, with an OAT of -10 degrees C in snow, noticed dropping manifold pressure. Was unable to engage carburetor heat. Requested and was given immediate approach to ILS 24 bdl. On short final, manifold pressure was just sufficient to maintain G/south at full throttle. After landing, carburetor heat could be engaged, suggesting that we had interfered with the linkage in some way. My mechanic recommends that anytime this aircraft is being operated in visible moisture, the carburetor heat should be engaged. Bdl approach did a super job of getting me in with no delay or distracting interrogations.

Original NASA ASRS Text

Title: GA SMA UNABLE TO CLEAR CARBURETOR ICE DECLARED AN EMERGENCY AND DIVERTED TO ALTERNATE.

Narrative: DEPARTED TEB, VFR TO BVY, HAVING OBTAINED WX FROM THE IVRS SYS, SATISFIED THAT VFR FLT WAS POSSIBLE. OVER THE HUDSON RIVER, 20 MI SSW OF PDU, SAW SNOW SHOWERS AHEAD AND CONTACTED PDU TWR FOR AN ARTCC FREQ TO REQUEST AN IFR CLRNC. OBTAINED PROMPT CLRNC TO 7000'. AT ABOUT 15 MI E OF BDL, WITH AN OAT OF -10 DEGS C IN SNOW, NOTICED DROPPING MANIFOLD PRESSURE. WAS UNABLE TO ENGAGE CARB HEAT. REQUESTED AND WAS GIVEN IMMEDIATE APCH TO ILS 24 BDL. ON SHORT FINAL, MANIFOLD PRESSURE WAS JUST SUFFICIENT TO MAINTAIN G/S AT FULL THROTTLE. AFTER LNDG, CARB HEAT COULD BE ENGAGED, SUGGESTING THAT WE HAD INTERFERED WITH THE LINKAGE IN SOME WAY. MY MECH RECOMMENDS THAT ANYTIME THIS ACFT IS BEING OPERATED IN VISIBLE MOISTURE, THE CARB HEAT SHOULD BE ENGAGED. BDL APCH DID A SUPER JOB OF GETTING ME IN WITH NO DELAY OR DISTRACTING INTERROGATIONS.

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.