C172 pilot experiences a rough running engine during a VOR approach and continues to a safe landing.

Attributes
ACN	1023340
Time
Date	201207
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Skyhawk 172/Cutlass 172
Operating Under FAR Part	Part 91
Flight Phase	Final Approach
Route In Use	Direct
Flight Plan	IFR
Component
Aircraft Component	Reciprocating Engine Assembly
Person 1
Function	Instructor
Qualification	Flight Crew Flight Instructor Flight Crew Commercial Flight Crew Instrument Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 50 Flight Crew Total 650 Flight Crew Type 600
Events
Anomaly	Aircraft Equipment Problem Critical

Narrative:

While on the VOR approach for 35L; noticed the engine started vibrating and loss of power. Went through the checklist and that didn't fix the issue. Declared an emergency and came in for 35R and landed without incident. Later found out from maintenance that the exhaust valve became blocked.

Original NASA ASRS Text

Title: C172 pilot experiences a rough running engine during a VOR approach and continues to a safe landing.

Narrative: While on the VOR approach for 35L; noticed the engine started vibrating and loss of power. Went through the checklist and that didn't fix the issue. Declared an emergency and came in for 35R and landed without incident. Later found out from Maintenance that the exhaust valve became blocked.

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.