B737 aircraft with automated flight guidance system deviated 200 ft above cleared altitude before ca...

Attributes
ACN	411990
Time
Date	199808
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : ihkh airport : mdw
State Reference	IL
Altitude	msl bound lower : 4000 msl bound upper : 4200
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ord
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	controller non radar : 3 controller radar : 2 flight time last 90 days : 130 flight time total : 13000 flight time type : 1500
ASRS Report	411990
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	altitude deviation : excursion from assigned altitude
Independent Detector	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:

First officer was the PF. Aircraft autoplt was engaged entire leg from msp to mdw. During the time of occurrence, however, I'm not sure if FMS was engaged or altitude hold. We were cleared for the ILS runway 4R approach to mdw (in VMC conditions) and instructed to 'maintain 4000 ft until cadon, cleared for ILS runway 4R approach, contact tower FAF inbound.' approximately 2-3 mi from cadon, first officer called for flaps 5 degrees. Upon reaching back from the flap handle, I noticed the aircraft climbing through 4200 ft. I simultaneously told the first officer to check his altitude, disconnected the autoplt and returned to 4000 ft MSL. At no time was another aircraft observed in the area nor an alert given (or warning) by TCASII or ATC.

Original NASA ASRS Text

Title: B737 ACFT WITH AUTOMATED FLT GUIDANCE SYS DEVIATED 200 FT ABOVE CLRED ALT BEFORE CAPT CORRECTED IT.

Narrative: FO WAS THE PF. ACFT AUTOPLT WAS ENGAGED ENTIRE LEG FROM MSP TO MDW. DURING THE TIME OF OCCURRENCE, HOWEVER, I'M NOT SURE IF FMS WAS ENGAGED OR ALT HOLD. WE WERE CLRED FOR THE ILS RWY 4R APCH TO MDW (IN VMC CONDITIONS) AND INSTRUCTED TO 'MAINTAIN 4000 FT UNTIL CADON, CLRED FOR ILS RWY 4R APCH, CONTACT TWR FAF INBOUND.' APPROX 2-3 MI FROM CADON, FO CALLED FOR FLAPS 5 DEGS. UPON REACHING BACK FROM THE FLAP HANDLE, I NOTICED THE ACFT CLBING THROUGH 4200 FT. I SIMULTANEOUSLY TOLD THE FO TO CHK HIS ALT, DISCONNECTED THE AUTOPLT AND RETURNED TO 4000 FT MSL. AT NO TIME WAS ANOTHER ACFT OBSERVED IN THE AREA NOR AN ALERT GIVEN (OR WARNING) BY TCASII OR ATC.

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.

B737 aircraft with automated flight guidance system deviated 200 ft above cleared altitude before captain corrected it.