Beech 58 pilot descends below assigned altitude while dealing with aircraft malfunction.

Attributes
ACN	438603
Time
Date	199905
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : 52f.airport
State Reference	TX
Altitude	msl bound lower : 2500 msl bound upper : 3000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : d10.tracon
Operator	general aviation : personal
Make Model Name	Baron 58/58TC
Operating Under FAR Part	Part 91
Flight Phase	descent : approach
Route In Use	arrival : on vectors
Flight Plan	IFR
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : multi engine pilot : instrument pilot : commercial
Experience	flight time last 90 days : 120 flight time total : 700 flight time type : 150
ASRS Report	438603
Person 2
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude inflight encounter other non adherence : far
Independent Detector	other controllera other flight crewa
Resolutory Action	none taken : anomaly accepted
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	ATC Human Performance Flight Crew Human Performance Aircraft
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Departed 52F at approximately XA00, IFR to dts. About 10 mins into the flight, the airplane developed a mechanical problem which I did not deem an emergency, but did require an immediate return to 52F. I advised dfw approach of my situation. He advised ads was closest airport. I felt I could make 52F. He gave me a heading back to 52F at 3000 ft MSL. About 3 mins from 52F the situation required a descent to maintain airspeed in safe range. At this moment, the controller handed me off to another controller. By the time the frequency cleared for me to speak, I had the problem under control but had descended to 2500 ft MSL. The controller asked if I had been cleared to 2500 ft. I advised 'no.' I was VMC at this time but still on IFR plan. I felt the undeclared emergency allowed me to deviate as necessary, however, I felt the need to send this in to protect myself. I landed safely at 52F and the control problem was fixed. We were on our way at XC00 again to dts without incident. In retrospect, I should have declared an emergency. The situation certainly warranted such a call. I was reluctant to do so.

Original NASA ASRS Text

Title: BEECH 58 PLT DSNDS BELOW ASSIGNED ALT WHILE DEALING WITH ACFT MALFUNCTION.

Narrative: DEPARTED 52F AT APPROX XA00, IFR TO DTS. ABOUT 10 MINS INTO THE FLT, THE AIRPLANE DEVELOPED A MECHANICAL PROB WHICH I DID NOT DEEM AN EMER, BUT DID REQUIRE AN IMMEDIATE RETURN TO 52F. I ADVISED DFW APCH OF MY SIT. HE ADVISED ADS WAS CLOSEST ARPT. I FELT I COULD MAKE 52F. HE GAVE ME A HDG BACK TO 52F AT 3000 FT MSL. ABOUT 3 MINS FROM 52F THE SIT REQUIRED A DSCNT TO MAINTAIN AIRSPD IN SAFE RANGE. AT THIS MOMENT, THE CTLR HANDED ME OFF TO ANOTHER CTLR. BY THE TIME THE FREQ CLRED FOR ME TO SPEAK, I HAD THE PROB UNDER CTL BUT HAD DSNDED TO 2500 FT MSL. THE CTLR ASKED IF I HAD BEEN CLRED TO 2500 FT. I ADVISED 'NO.' I WAS VMC AT THIS TIME BUT STILL ON IFR PLAN. I FELT THE UNDECLARED EMER ALLOWED ME TO DEVIATE AS NECESSARY, HOWEVER, I FELT THE NEED TO SEND THIS IN TO PROTECT MYSELF. I LANDED SAFELY AT 52F AND THE CTL PROB WAS FIXED. WE WERE ON OUR WAY AT XC00 AGAIN TO DTS WITHOUT INCIDENT. IN RETROSPECT, I SHOULD HAVE DECLARED AN EMER. THE SIT CERTAINLY WARRANTED SUCH A CALL. I WAS RELUCTANT TO DO SO.

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.