An M-7 pilot flying IFR in rain was unable to maintain power and requested ATC vectors to a nearby a...

Attributes
ACN	1018031
Time
Date	201206
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Make Model Name	M-7
Operating Under FAR Part	Part 91
Flight Phase	Cruise
Route In Use	Vectors
Flight Plan	IFR
Component
Aircraft Component	Engine
Person 1
Function	Single Pilot Pilot Flying
Qualification	Flight Crew Multiengine Flight Crew Commercial Flight Crew Flight Instructor
Experience	Flight Crew Last 90 Days 120 Flight Crew Total 630 Flight Crew Type 5
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Altitude Excursion From Assigned Altitude Inflight Event / Encounter Weather / Turbulence

Narrative:

I was flying a maule into IMC and light rain while being vectored around thunderstorms at 4;000 MSL. As I began flying through the clouds I turned on the carb heat in order to keep ice from forming in the carburetor. As soon as the rain began; the engine ran a little rough and progressively began choking. At full throttle it was only putting out 1;500 RPM. This was not sufficient thrust to maintain altitude. Throughout this incident I lost 500 ft from my on course altitude. The controller mentioned that my altitude was indicating lower than 4;000 ft. I told the controller I was unable to maintain altitude and that I wanted vectors to the nearest airport. The controller did a fantastic job redirecting me to the nearest airport and I was able to land the aircraft without incident.

Original NASA ASRS Text

Title: An M-7 pilot flying IFR in rain was unable to maintain power and requested ATC vectors to a nearby airport where a safe landing was accomplished.

Narrative: I was flying a Maule into IMC and light rain while being vectored around thunderstorms at 4;000 MSL. As I began flying through the clouds I turned on the carb heat in order to keep ice from forming in the carburetor. As soon as the rain began; the engine ran a little rough and progressively began choking. At full throttle it was only putting out 1;500 RPM. This was not sufficient thrust to maintain altitude. Throughout this incident I lost 500 FT from my on course altitude. The Controller mentioned that my altitude was indicating lower than 4;000 FT. I told the Controller I was unable to maintain altitude and that I wanted vectors to the nearest airport. The Controller did a fantastic job redirecting me to the nearest airport and I was able to land the aircraft without incident.

Data retrieved from NASA's ASRS site as of July 2013 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.