From the NASA database:
FAA pilot of a cessna 177RG experienced engine failure during IMC operations caused by air intake impact icing. The engine self started after the aircraft involuntarily descended to a lower altitude and a successful landing was subsequently made.
Time
Date 199612
Day Mon
Local Time Of Day 0601 To 1200
Place
Locale Reference airport : olm
State Reference WA
Altitude msl bound lower : 9000
msl bound upper : 9000
Environment
Flight Conditions IMC
Light Daylight
Aircraft 1
Operator other
Make Model Name Cardinal 177/177RG
Operating Under FAR Part Part 91
Flight Phase cruise other
Route In Use enroute airway : zse
Flight Plan IFR
Person 1
Affiliation government other
Function flight crew : single pilot
Qualification other other : other
pilot : commercial
pilot : instrument
pilot : cfi
pilot : atp
Experience flight time last 90 days : 50
flight time total : 2500
flight time type : 50
ASRS Report 354582
Person 2
Affiliation government : faa
Function controller : radar
Qualification controller : radar
Events
Anomaly aircraft equipment problem : critical
other anomaly other
Independent Detector other flight crewa
Resolutory Action aircraft : equipment problem dissipated
flight crew : exited adverse environment
Consequence faa : investigated
Other
Supplementary
Primary Problem Aircraft
Air Traffic Incident other
Narrative:
Cruising at 9000 ft MSL, sbound on V165 with no ice accumulating on wing or tail leading edges. Outside air temperature approximately minus 12 degrees C. Conditions were IMC in clouds. Engine manifold pressure dropped abruptly from 21 inches to 15 inches. Informed ATC, asked for approach into olympia, and completed emergency checklist. About 45 seconds after initial partial power loss, complete engine power loss occurred. Then declared emergency, and asked for vector to nearest airport. Set up glide for toledo, wa, airport using handheld GPS and controller vectors. Was informed that ceiling at toledo was 1000 ft. At 4000 ft MSL, engine came back to life. Airplane is 1976 cessna 177RG with I0360 engine. When engine restarted, asked for and was cleared for ILS to olympia. Landed without further incident. This airplane has fuel-injected engine with 'automatic' alternate induction air source. After landing, found air filter about 1/2 blocked with ice. I believe that part of the ice must have fallen off at 4000 ft allowing engine to restart. No ice was visible elsewhere on airframe where pilot could see it from cockpit. Since the engine did not surge as is typical with the operation of a spring loaded automatic alternate air source, I don't believe the alternate door ever opened. Design is bad since alternate door is at front of engine, unheated, and is nearly as susceptible to icing as the primary air filter. All reciprocating engine airplanes should have heated alternate air sources with the ability for pilot to manually open if chooses. This would prevent such a power loss in event of inadvertent induction icing. Mechanic's inspection found alternate air door ok per maintenance manual. Callback conversation with reporter revealed the following information: reporter stated that he submitted a safety recommendation to the FAA office of accident investigation, recommendation and quality assurance division (aai-200) of this matter recommending a fix that would allow the pilot to manually control the opening of the alternate air intake door. He believes that this system was never adequately reviewed prior to giving cessna FAA ok of the system. The reporter believes that this is a good example of why the alternate intake door should not be totally automatic. In addition, this system would not meet the current certification rules for the minimum air temperature required for the location of the alternate intake door opening.