Altitude deviation altitude overshot during aircraft equipment problem malfunction.

Attributes
ACN	223671
Time
Date	199210
Day	Sat
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : dca
State Reference	DC
Altitude	msl bound lower : 4000 msl bound upper : 4500
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	tracon : dca
Operator	other
Make Model Name	Small Aircraft, High Wing, 1 Eng, Retractable Gear
Flight Phase	cruise other cruise other descent : approach
Route In Use	approach : visual
Flight Plan	VFR
Person 1
Affiliation	government other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : commercial pilot : cfi
Experience	flight time last 90 days : 40 flight time total : 2318 flight time type : 14
ASRS Report	223671
Person 2
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude altitude deviation : overshoot non adherence : clearance other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : overcame equipment problem flight crew : returned to intended course or assigned course
Consequence	Other

Narrative:

I was on a visual approach into dca under VMC. Washington approach instructed me to descend to and maintain 4500 ft. I complied and put the aircraft on altitude hold using an autoplt system. While level at this altitude, with the autoplt engaged, the aircraft started to descend. I attempted to shut the autoplt off. The autoplt indicator lights indicated it was off, however, the autoplt failed to disengage. I was unable to manually arrest the descent. I pulled the autoplt circuit breaker, regained control of the aircraft, stopped the descent at 4000 ft and manually flew the aircraft back to 4500 ft. The rest of the approach and landing was uneventful. There did not appear to be any traffic conflict. I filled out a maintenance discrepancy report upon my return to bwi that evening. Maintenance pulled the autoplt on 10/wed/92 and sent it to the factory for repair. Lesson: everybody should know the exact location of the circuit breakers for each piece of electrical equipment. 'George' doesn't always work, sometimes he takes a holiday.

Original NASA ASRS Text

Title: ALTDEV ALT OVERSHOT DURING ACFT EQUIP PROBLEM MALFUNCTION.

Narrative: I WAS ON A VISUAL APCH INTO DCA UNDER VMC. WASHINGTON APCH INSTRUCTED ME TO DSND TO AND MAINTAIN 4500 FT. I COMPLIED AND PUT THE ACFT ON ALT HOLD USING AN AUTOPLT SYS. WHILE LEVEL AT THIS ALT, WITH THE AUTOPLT ENGAGED, THE ACFT STARTED TO DSND. I ATTEMPTED TO SHUT THE AUTOPLT OFF. THE AUTOPLT INDICATOR LIGHTS INDICATED IT WAS OFF, HOWEVER, THE AUTOPLT FAILED TO DISENGAGE. I WAS UNABLE TO MANUALLY ARREST THE DSCNT. I PULLED THE AUTOPLT CIRCUIT BREAKER, REGAINED CTL OF THE ACFT, STOPPED THE DSCNT AT 4000 FT AND MANUALLY FLEW THE ACFT BACK TO 4500 FT. THE REST OF THE APCH AND LNDG WAS UNEVENTFUL. THERE DID NOT APPEAR TO BE ANY TFC CONFLICT. I FILLED OUT A MAINT DISCREPANCY RPT UPON MY RETURN TO BWI THAT EVENING. MAINT PULLED THE AUTOPLT ON 10/WED/92 AND SENT IT TO THE FACTORY FOR REPAIR. LESSON: EVERYBODY SHOULD KNOW THE EXACT LOCATION OF THE CIRCUIT BREAKERS FOR EACH PIECE OF ELECTRICAL EQUIP. 'GEORGE' DOESN'T ALWAYS WORK, SOMETIMES HE TAKES A HOLIDAY.

Data retrieved from NASA's ASRS site as of July 2007 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.