Aircraft equipment problem critical. Altitude deviation excursion from assigned.

Attributes
ACN	292269
Time
Date	199412
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : jct
State Reference	TX
Altitude	msl bound lower : 8000 msl bound upper : 9000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Operator	general aviation : personal
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 91
Flight Phase	cruise other other other
Route In Use	enroute airway : zhu
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : private
Experience	flight time last 90 days : 47 flight time total : 1146 flight time type : 465
ASRS Report	292269
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	controller : issued new clearance flight crew : exited adverse environment flight crew : declared emergency
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

I was IMC in moderate rain at 9000 ft (freezing level was 9000-10000 ft ice forecast above 12000 ft. During which time, I was asking center for advisories around the heavy thunderstorms ahead and at the same time using stormscope to avoid most of it. I was having trouble maintaining altitude and told center. Also I informed them I would like to deviation as necessary which was okay with them. I only busted my assigned altitude for not more than 2-3 mins plus or minus 400 ft on 2 occasions. On the other radio I had FSS/hou). Traffic it seems, was to backtrack, fly 50 mi east, then back south. (Jct-sat). After advising center of this, they asked me to descend to 8000 ft because of my direction of flight, which I proceeded to do until my alternator failed at which time considering: a) I needed the pitot heat on, B) I needed navigation information, C) the battery would discharge very rapidly: I declared an emergency and was given radar vectors back to junction where I had an uneventful landing. I discovered the problem because my aircraft is equipped with a low voltage light. Human performance considerations. A) I had just flown that same route 1 hour and 45 min earlier and I knew where the heavy WX was. B) I was delayed 1 hour at junction to await the arrival of another aircraft with deteriorating WX. Contributing factors: possibility of ice, heavy rain (which I later found out caused the problem) and turbulence.

Original NASA ASRS Text

Title: ACFT EQUIP PROB CRITICAL. ALTDEV EXCURSION FROM ASSIGNED.

Narrative: I WAS IMC IN MODERATE RAIN AT 9000 FT (FREEZING LEVEL WAS 9000-10000 FT ICE FORECAST ABOVE 12000 FT. DURING WHICH TIME, I WAS ASKING CTR FOR ADVISORIES AROUND THE HVY TSTMS AHEAD AND AT THE SAME TIME USING STORMSCOPE TO AVOID MOST OF IT. I WAS HAVING TROUBLE MAINTAINING ALT AND TOLD CTR. ALSO I INFORMED THEM I WOULD LIKE TO DEV AS NECESSARY WHICH WAS OKAY WITH THEM. I ONLY BUSTED MY ASSIGNED ALT FOR NOT MORE THAN 2-3 MINS PLUS OR MINUS 400 FT ON 2 OCCASIONS. ON THE OTHER RADIO I HAD FSS/HOU). TFC IT SEEMS, WAS TO BACKTRACK, FLY 50 MI E, THEN BACK S. (JCT-SAT). AFTER ADVISING CTR OF THIS, THEY ASKED ME TO DSND TO 8000 FT BECAUSE OF MY DIRECTION OF FLT, WHICH I PROCEEDED TO DO UNTIL MY ALTERNATOR FAILED AT WHICH TIME CONSIDERING: A) I NEEDED THE PITOT HEAT ON, B) I NEEDED NAV INFO, C) THE BATTERY WOULD DISCHARGE VERY RAPIDLY: I DECLARED AN EMER AND WAS GIVEN RADAR VECTORS BACK TO JUNCTION WHERE I HAD AN UNEVENTFUL LNDG. I DISCOVERED THE PROB BECAUSE MY ACFT IS EQUIPPED WITH A LOW VOLTAGE LIGHT. HUMAN PERFORMANCE CONSIDERATIONS. A) I HAD JUST FLOWN THAT SAME RTE 1 HR AND 45 MIN EARLIER AND I KNEW WHERE THE HVY WX WAS. B) I WAS DELAYED 1 HR AT JUNCTION TO AWAIT THE ARR OF ANOTHER ACFT WITH DETERIORATING WX. CONTRIBUTING FACTORS: POSSIBILITY OF ICE, HVY RAIN (WHICH I LATER FOUND OUT CAUSED THE PROB) AND TURB.

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.