Cpr pilot of AC690 erroneously deviated from assigned altitude in turbulence on approach to mdw, il.

Attributes
ACN	421197
Time
Date	199811
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : mdw
State Reference	IL
Altitude	msl bound lower : 4000 msl bound upper : 4700
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ord
Operator	general aviation : corporate
Make Model Name	Turbo Commander 690C
Operating Under FAR Part	Part 91
Flight Phase	cruise other descent other
Route In Use	arrival other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	oversight : pic
Qualification	pilot : cfi pilot : commercial pilot : instrument
Experience	flight time last 90 days : 130 flight time total : 7100 flight time type : 35
ASRS Report	421197
Person 2
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude inflight encounter : weather non adherence : clearance
Independent Detector	atc equipment other atc equipment : unspecified other controllera other flight crewa
Resolutory Action	controller : issued new clearance flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

I was en route from rac to mdw and had contacted ord approach. I was assigned a heading and told to expect an ILS approach at mdw. I was at my assigned altitude of 4000 ft with my autoplt engaged. While I was setting up the approach the airplane was being rocked by moderate turbulence. Approach asked me about my altitude and I realized I was at 4600 ft descending at 400 FPM. The altitude hold on the autoplt had disengaged and I had climbed out of my assigned altitude without noticing. I told approach what had happened and apologized. They told me to maintain 4000 ft and the flight continued without incident.

Original NASA ASRS Text

Title: CPR PLT OF AC690 ERRONEOUSLY DEVIATED FROM ASSIGNED ALT IN TURB ON APCH TO MDW, IL.

Narrative: I WAS ENRTE FROM RAC TO MDW AND HAD CONTACTED ORD APCH. I WAS ASSIGNED A HDG AND TOLD TO EXPECT AN ILS APCH AT MDW. I WAS AT MY ASSIGNED ALT OF 4000 FT WITH MY AUTOPLT ENGAGED. WHILE I WAS SETTING UP THE APCH THE AIRPLANE WAS BEING ROCKED BY MODERATE TURB. APCH ASKED ME ABOUT MY ALT AND I REALIZED I WAS AT 4600 FT DSNDING AT 400 FPM. THE ALT HOLD ON THE AUTOPLT HAD DISENGAGED AND I HAD CLBED OUT OF MY ASSIGNED ALT WITHOUT NOTICING. I TOLD APCH WHAT HAD HAPPENED AND APOLOGIZED. THEY TOLD ME TO MAINTAIN 4000 FT AND THE FLT CONTINUED WITHOUT INCIDENT.

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.