Mooney M20R has a malfunctioning engine during approach.

Attributes
ACN	718711
Time
Date	200611
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl single value : 3000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : zzz.tracon
Operator	general aviation : personal
Make Model Name	M-20 Series Undifferentiated or Other Model
Operating Under FAR Part	Part 91
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : commercial pilot : cfi pilot : multi engine pilot : instrument
Experience	flight time last 90 days : 100 flight time total : 7500 flight time type : 2000
ASRS Report	718711
Person 2
Affiliation	government : faa
Function	controller : approach
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : landed as precaution
Consequence	faa : reviewed incident with flight crew other
Supplementary
Problem Areas	ATC Human Performance Aircraft Flight Crew Human Performance
Primary Problem	Aircraft

Narrative:

I was on an IFR flight plan. On the descent into ZZZ; I was advised that I was #6 for the approach and could expect a long downwind vector. I was in class east airspace in VFR/VMC conditions and advised ATC that I wanted to cancel IFR and proceed visually to the airport. ATC replied; 'negative; remain IFR.' I did not believe that ATC had the authority/authorized (or the justification) to issue such a clearance. I complied with the clearance and continued on my northbound vector. Within 1 min; my engine started running so rough that I declared that I needed to land immediately. Because the shaking was so violent; I was unable to establish communication with approach; in spite of attempting on 2 radios with 2 different headsets. I could hear approach state that I needed to continue northbound. I circled adjacent to the airport while looking for a light gun signal. I was able to establish communication on a hand microphone with approach and restated that I needed to land immediately and was switched to local control. I landed immediately and was told to call approach. My aircraft was towed to a maintenance facility where it was determined that my magneto failed in such a way as to cause misfiring. Approach was upset with me as they incorrectly believed that I 'faked' an emergency to expedite my landing clearance. I experienced an actual in-flight emergency that could have been made much worse because of the incorrect and petty actions of ATC. Because of the compressed timeframe these events unfolded; I was unable to use the word emergency or mayday until after touchdown.

Original NASA ASRS Text

Title: MOONEY M20R HAS A MALFUNCTIONING ENG DURING APCH.

Narrative: I WAS ON AN IFR FLT PLAN. ON THE DSCNT INTO ZZZ; I WAS ADVISED THAT I WAS #6 FOR THE APCH AND COULD EXPECT A LONG DOWNWIND VECTOR. I WAS IN CLASS E AIRSPACE IN VFR/VMC CONDITIONS AND ADVISED ATC THAT I WANTED TO CANCEL IFR AND PROCEED VISUALLY TO THE ARPT. ATC REPLIED; 'NEGATIVE; REMAIN IFR.' I DID NOT BELIEVE THAT ATC HAD THE AUTH (OR THE JUSTIFICATION) TO ISSUE SUCH A CLRNC. I COMPLIED WITH THE CLRNC AND CONTINUED ON MY NBOUND VECTOR. WITHIN 1 MIN; MY ENG STARTED RUNNING SO ROUGH THAT I DECLARED THAT I NEEDED TO LAND IMMEDIATELY. BECAUSE THE SHAKING WAS SO VIOLENT; I WAS UNABLE TO ESTABLISH COM WITH APCH; IN SPITE OF ATTEMPTING ON 2 RADIOS WITH 2 DIFFERENT HEADSETS. I COULD HEAR APCH STATE THAT I NEEDED TO CONTINUE NBOUND. I CIRCLED ADJACENT TO THE ARPT WHILE LOOKING FOR A LIGHT GUN SIGNAL. I WAS ABLE TO ESTABLISH COM ON A HAND MIKE WITH APCH AND RESTATED THAT I NEEDED TO LAND IMMEDIATELY AND WAS SWITCHED TO LCL CTL. I LANDED IMMEDIATELY AND WAS TOLD TO CALL APCH. MY ACFT WAS TOWED TO A MAINT FACILITY WHERE IT WAS DETERMINED THAT MY MAGNETO FAILED IN SUCH A WAY AS TO CAUSE MISFIRING. APCH WAS UPSET WITH ME AS THEY INCORRECTLY BELIEVED THAT I 'FAKED' AN EMER TO EXPEDITE MY LNDG CLRNC. I EXPERIENCED AN ACTUAL INFLT EMER THAT COULD HAVE BEEN MADE MUCH WORSE BECAUSE OF THE INCORRECT AND PETTY ACTIONS OF ATC. BECAUSE OF THE COMPRESSED TIMEFRAME THESE EVENTS UNFOLDED; I WAS UNABLE TO USE THE WORD EMER OR MAYDAY UNTIL AFTER TOUCHDOWN.

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.