C172 pilot experiences a rough running engine at 11;000 feet; which is believed to be caused by inta...

Attributes
ACN	1249173
Time
Date	201503
Local Time Of Day	1201-1800
Place
Locale Reference	CEC.Airport
State Reference	CA
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Make Model Name	Skyhawk 172/Cutlass 172
Operating Under FAR Part	Part 91
Flight Phase	Descent
Route In Use	Direct Airway V27
Flight Plan	IFR
Component
Aircraft Component	Reciprocating Engine Assembly
Person 1
Function	Single Pilot Pilot Flying
Qualification	Flight Crew Instrument Flight Crew Private
Experience	Flight Crew Last 90 Days 41 Flight Crew Total 296 Flight Crew Type 156
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Published Material / Policy Inflight Event / Encounter CFTT / CFIT Inflight Event / Encounter Weather / Turbulence

Narrative:

While enroute to cec along V27 at 11000 MSL; the engine began to run rough. The flight was in solid IMC and there was intermittent icy precipitation. Various combinations of carburetor heat and mixture provided only temporary relief; and as time progressed the roughness worsened. Suspected cause was ice buildup in the engine intake. Pilot requested a descent and was granted permission to descend to 7000 (MEA was 6400). Engine began to run more smoothly; but the need was apparent to descend to warmer conditions as soon as possible to allow suspected intake ice to melt.shortly thereafter; ATC cleared the aircraft for the cec RNAV (GPS) runway 11 approach. The wipog feeder route for the IAF shows 4000 MSL; but the descent was started immediately instead of waiting for wipog. ATC noticed the early descent and issued a terrain warning with instructions to immediately climb to 6400. Contributing factors were (1) flight in near icing conditions; (2) poorly designed engine intake; (3) fear of worsening engine problems; (4) lack of experience in the IFR system (pilot's first IMC flight after adding the instrument rating).

Original NASA ASRS Text

Title: C172 pilot experiences a rough running engine at 11;000 feet; which is believed to be caused by intake icing. A descent to 7;000 feet is requested and granted which lead to improved power but still rough. A clearance is issued for the RNAV RWY 11 Approach at CEC; but descent is initiated prior to WIPOG resulting in ATC issuing a terrain warning. The reporter is able to climb back to 6;400 feet until WIPOG and complete the approach.

Narrative: While enroute to CEC along V27 at 11000 MSL; the engine began to run rough. The flight was in solid IMC and there was intermittent icy precipitation. Various combinations of carburetor heat and mixture provided only temporary relief; and as time progressed the roughness worsened. Suspected cause was ice buildup in the engine intake. Pilot requested a descent and was granted permission to descend to 7000 (MEA was 6400). Engine began to run more smoothly; but the need was apparent to descend to warmer conditions as soon as possible to allow suspected intake ice to melt.Shortly thereafter; ATC cleared the aircraft for the CEC RNAV (GPS) RWY 11 approach. The WIPOG feeder route for the IAF shows 4000 MSL; but the descent was started immediately instead of waiting for WIPOG. ATC noticed the early descent and issued a terrain warning with instructions to immediately climb to 6400. Contributing factors were (1) Flight in near icing conditions; (2) Poorly designed engine intake; (3) Fear of worsening engine problems; (4) Lack of experience in the IFR system (pilot's first IMC flight after adding the instrument rating).

Data retrieved from NASA's ASRS site 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.