PA-28 pilot has an engine malfunction during approach to roc.

Attributes
ACN	725353
Time
Date	200701
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl single value : 2500
Environment
Flight Conditions	IMC
Weather Elements	Fog Snow
Light	Night
Aircraft 1
Controlling Facilities	tracon : zzz.tracon
Operator	general aviation : personal
Make Model Name	PA-28 Cherokee/Archer II/Dakota/Pillan/Warrior
Operating Under FAR Part	Part 91
Flight Phase	descent : approach ground : maintenance
Flight Plan	IFR
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : private pilot : instrument
Experience	flight time last 90 days : 50 flight time total : 225 flight time type : 221
ASRS Report	725353
Person 2
Affiliation	government : faa
Function	controller : approach
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	other flight crewa
Resolutory Action	controller : provided flight assist flight crew : declared emergency flight crew : landed in emergency condition
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

Airplane on ZZZ ILS runway 22 approach experienced a loss of power and strong vibration consistent with a failure of 1 cylinder. Prior to incident; airplane was ready for landing. Landing checklist had been performed and carburetor heat was on. Approximately 1 mi from FAF; engine ran rough and lost significant power. Airplane was unable to maintain altitude and began descent below GS before reaching FAF. Throttle was increased from approximately 50% to full power; carburetor heat was turned off yielding a performance increase. Emergency checklist was performed and best glide speed established with full throttle. Emergency was declared and vectors were given by ATC to maintain localizer. ATC advised that terrain allowed operation below GS. ATC also handed off all other traffic to different frequency. The airplane broke through clouds 1000 ft AGL and runway was in sight. Airplane contacted the runway on the threshold. Landing continued without incident. No damages were incurred.

Original NASA ASRS Text

Title: PA-28 PLT HAS AN ENG MALFUNCTION DURING APCH TO ROC.

Narrative: AIRPLANE ON ZZZ ILS RWY 22 APCH EXPERIENCED A LOSS OF PWR AND STRONG VIBRATION CONSISTENT WITH A FAILURE OF 1 CYLINDER. PRIOR TO INCIDENT; AIRPLANE WAS READY FOR LNDG. LNDG CHKLIST HAD BEEN PERFORMED AND CARB HEAT WAS ON. APPROX 1 MI FROM FAF; ENG RAN ROUGH AND LOST SIGNIFICANT PWR. AIRPLANE WAS UNABLE TO MAINTAIN ALT AND BEGAN DSCNT BELOW GS BEFORE REACHING FAF. THROTTLE WAS INCREASED FROM APPROX 50% TO FULL PWR; CARB HEAT WAS TURNED OFF YIELDING A PERFORMANCE INCREASE. EMER CHKLIST WAS PERFORMED AND BEST GLIDE SPD ESTABLISHED WITH FULL THROTTLE. EMER WAS DECLARED AND VECTORS WERE GIVEN BY ATC TO MAINTAIN LOC. ATC ADVISED THAT TERRAIN ALLOWED OP BELOW GS. ATC ALSO HANDED OFF ALL OTHER TFC TO DIFFERENT FREQ. THE AIRPLANE BROKE THROUGH CLOUDS 1000 FT AGL AND RWY WAS IN SIGHT. AIRPLANE CONTACTED THE RWY ON THE THRESHOLD. LNDG CONTINUED WITHOUT INCIDENT. NO DAMAGES WERE INCURRED.

Data retrieved from NASA's ASRS site as of January 2009 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.