FAA PLT OF A CESSNA 177RG EXPERIENCED ENG FAILURE DURING IMC OPS CAUSED BY AIR INTAKE IMPACT ICING. THE ENG SELF STARTED AFTER THE ACFT INVOLUNTARILY DSNDED TO A LOWER ALT AND A SUCCESSFUL LNDG WAS SUBSEQUENTLY MADE.

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CRUISING AT 9000 FT MSL; SBOUND ON V165 WITH NO ICE ACCUMULATING ON WING OR TAIL LEADING EDGES. OUTSIDE AIR TEMP APPROX MINUS 12 DEGS C. CONDITIONS WERE IMC IN CLOUDS. ENG MANIFOLD PRESSURE DROPPED ABRUPTLY FROM 21 INCHES TO 15 INCHES. INFORMED ATC; ASKED FOR APCH INTO OLYMPIA; AND COMPLETED EMER CHKLIST. ABOUT 45 SECONDS AFTER INITIAL PARTIAL PWR LOSS; COMPLETE ENG PWR LOSS OCCURRED. THEN DECLARED EMER; AND ASKED FOR VECTOR TO NEAREST ARPT. SET UP GLIDE FOR TOLEDO; WA; ARPT USING HANDHELD GPS AND CTLR VECTORS. WAS INFORMED THAT CEILING AT TOLEDO WAS 1000 FT. AT 4000 FT MSL; ENG CAME BACK TO LIFE. AIRPLANE IS 1976 CESSNA 177RG WITH I0360 ENG. WHEN ENG RESTARTED; ASKED FOR AND WAS CLRED FOR ILS TO OLYMPIA. LANDED WITHOUT FURTHER INCIDENT. THIS AIRPLANE HAS FUEL-INJECTED ENG WITH 'AUTOMATIC' ALTERNATE INDUCTION AIR SOURCE. AFTER LNDG; FOUND AIR FILTER ABOUT 1/2 BLOCKED WITH ICE. I BELIEVE THAT PART OF THE ICE MUST HAVE FALLEN OFF AT 4000 FT ALLOWING ENG TO RESTART. NO ICE WAS VISIBLE ELSEWHERE ON AIRFRAME WHERE PLT COULD SEE IT FROM COCKPIT. SINCE THE ENG DID NOT SURGE AS IS TYPICAL WITH THE OP 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 ENG; 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 PLT TO MANUALLY OPEN IF CHOOSES. THIS WOULD PREVENT SUCH A PWR LOSS IN EVENT OF INADVERTENT INDUCTION ICING. MECH'S INSPECTION FOUND ALTERNATE AIR DOOR OK PER MAINT MANUAL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR 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 PLT TO MANUALLY CTL THE OPENING OF THE ALTERNATE AIR INTAKE DOOR. HE BELIEVES THAT THIS SYS WAS NEVER ADEQUATELY REVIEWED PRIOR TO GIVING CESSNA FAA OK OF THE SYS. THE RPTR BELIEVES THAT THIS IS A GOOD EXAMPLE OF WHY THE ALTERNATE INTAKE DOOR SHOULD NOT BE TOTALLY AUTOMATIC. IN ADDITION; THIS SYS WOULD NOT MEET THE CURRENT CERTIFICATION RULES FOR THE MINIMUM AIR TEMP REQUIRED FOR THE LOCATION OF THE ALTERNATE INTAKE DOOR OPENING.