Small aircraft pilot on IFR flight plan deviates from assigned altitude.

Attributes
ACN	147352
Time
Date	199006
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : eon
State Reference	IL
Altitude	msl bound lower : 4700 msl bound upper : 5000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zau
Operator	general aviation : personal
Make Model Name	Small Aircraft, High Wing, 1 Eng, Fixed Gear
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : commercial
Experience	flight time last 90 days : 100 flight time total : 1500 flight time type : 10
ASRS Report	147352
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other controllera other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Assigned 5000' which put me 1000' on top (tops 4000') with high thin cirrus above. While maintain a lookout for other traffic, since I was VMC, my INS scan became a little lax and I slipped down in altitude. I caught myself at 240' low and ATC called me at 300' low. I had started back to my assigned altitude and ATC gave me a new altimeter setting, then said, 'ok, I have you level now.' my perception is work harder at the INS scan and maintain the altitude. The only other aircraft around would also be on radar and ATC would call them out to me (I hope). A contributing factor--the aircraft is not equipped with autoplt.

Original NASA ASRS Text

Title: SMA PLT ON IFR FLT PLAN DEVIATES FROM ASSIGNED ALT.

Narrative: ASSIGNED 5000' WHICH PUT ME 1000' ON TOP (TOPS 4000') WITH HIGH THIN CIRRUS ABOVE. WHILE MAINTAIN A LOOKOUT FOR OTHER TFC, SINCE I WAS VMC, MY INS SCAN BECAME A LITTLE LAX AND I SLIPPED DOWN IN ALT. I CAUGHT MYSELF AT 240' LOW AND ATC CALLED ME AT 300' LOW. I HAD STARTED BACK TO MY ASSIGNED ALT AND ATC GAVE ME A NEW ALTIMETER SETTING, THEN SAID, 'OK, I HAVE YOU LEVEL NOW.' MY PERCEPTION IS WORK HARDER AT THE INS SCAN AND MAINTAIN THE ALT. THE ONLY OTHER ACFT AROUND WOULD ALSO BE ON RADAR AND ATC WOULD CALL THEM OUT TO ME (I HOPE). A CONTRIBUTING FACTOR--THE ACFT IS NOT EQUIPPED WITH AUTOPLT.

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.