Small transport pilot had altitude excursion.

Attributes
ACN	447040
Time
Date	199908
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	navaid : mem.vortac
State Reference	TN
Altitude	msl bound lower : 7000 msl bound upper : 7700
Environment
Flight Conditions	VMC
Weather Elements	Thunderstorm
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zme.artcc tower : atl.tower
Operator	common carrier : air carrier
Make Model Name	Small Transport, Low Wing, 2 Turboprop Eng
Operating Under FAR Part	Part 135
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : single pilot oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 53 flight time total : 21980
ASRS Report	447040
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued alert flight crew : returned to assigned altitude
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

While cruising at assigned IFR altitude of 7000 ft and distracted by monitoring progress of flight around thunderstorms, the altitude hold portion of the autoplt unknowingly became disengaged, allowing the aircraft to slowly climb to 7700 ft, at which time ZME asked what my altitude was. I responded to them and immediately descended to 7000 ft. Aircraft was being flown single pilot and was not equipped with an altitude alerter, both of which (2 pilots and altitude alerter) would have helped prevent this diversion from assigned altitude.

Original NASA ASRS Text

Title: SMT PLT HAD ALT EXCURSION.

Narrative: WHILE CRUISING AT ASSIGNED IFR ALT OF 7000 FT AND DISTRACTED BY MONITORING PROGRESS OF FLT AROUND TSTMS, THE ALT HOLD PORTION OF THE AUTOPLT UNKNOWINGLY BECAME DISENGAGED, ALLOWING THE ACFT TO SLOWLY CLB TO 7700 FT, AT WHICH TIME ZME ASKED WHAT MY ALT WAS. I RESPONDED TO THEM AND IMMEDIATELY DSNDED TO 7000 FT. ACFT WAS BEING FLOWN SINGLE PLT AND WAS NOT EQUIPPED WITH AN ALT ALERTER, BOTH OF WHICH (2 PLTS AND ALT ALERTER) WOULD HAVE HELPED PREVENT THIS DIVERSION FROM ASSIGNED ALT.

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.