An A300-600 climbed through assigned altitude because autoplt failed to capture.

Attributes
ACN	716977
Time
Date	200611
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : mem.vortac
State Reference	TN
Altitude	msl bound lower : 26000 msl bound upper : 26500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zme.artcc
Operator	common carrier : air carrier
Make Model Name	A300
Operating Under FAR Part	Part 121
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : atp pilot : cfi
Experience	flight time last 90 days : 70 flight time total : 6000 flight time type : 1300
ASRS Report	716977
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	altitude deviation : overshoot inflight encounter : turbulence non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to assigned altitude
Supplementary
Problem Areas	Aircraft Weather Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance

Narrative:

Climbing through FL240 entered area of light then moderate turbulence. Airspeed increased into red zipper. Disengaged autothrottles but remained in profile climb mode. Autoplt overshot altitude by +250 ft and still climbing. Disconnected autoplt and began descent from FL265 to FL260. Profile mode would not maintain altitude so engaged altitude hold at FL260. We advised ATC of the deviation. Factors: we were paralleling a frontal boundary in the climb. In the A300/310 profile mode has reduced elevator control. When airspeed jumped approximately +15 KTS to overspd; that became our primary concern in climb. By the way; the overspd warning is the same as an engine; APU; or cargo fire. It takes a minute to analyze the warning. The next morning; our company issued an airworthiness directive from the FAA about altitude overshoots in turbulence while in profile climb mode. I had never seen or heard of this problem before.

Original NASA ASRS Text

Title: AN A300-600 CLBED THROUGH ASSIGNED ALT BECAUSE AUTOPLT FAILED TO CAPTURE.

Narrative: CLBING THROUGH FL240 ENTERED AREA OF LIGHT THEN MODERATE TURB. AIRSPD INCREASED INTO RED ZIPPER. DISENGAGED AUTOTHROTTLES BUT REMAINED IN PROFILE CLB MODE. AUTOPLT OVERSHOT ALT BY +250 FT AND STILL CLBING. DISCONNECTED AUTOPLT AND BEGAN DSCNT FROM FL265 TO FL260. PROFILE MODE WOULD NOT MAINTAIN ALT SO ENGAGED ALT HOLD AT FL260. WE ADVISED ATC OF THE DEV. FACTORS: WE WERE PARALLELING A FRONTAL BOUNDARY IN THE CLB. IN THE A300/310 PROFILE MODE HAS REDUCED ELEVATOR CTL. WHEN AIRSPD JUMPED APPROX +15 KTS TO OVERSPD; THAT BECAME OUR PRIMARY CONCERN IN CLB. BY THE WAY; THE OVERSPD WARNING IS THE SAME AS AN ENG; APU; OR CARGO FIRE. IT TAKES A MINUTE TO ANALYZE THE WARNING. THE NEXT MORNING; OUR COMPANY ISSUED AN AIRWORTHINESS DIRECTIVE FROM THE FAA ABOUT ALT OVERSHOOTS IN TURB WHILE IN PROFILE CLB MODE. I HAD NEVER SEEN OR HEARD OF THIS PROB BEFORE.

Data retrieved from NASA's ASRS site as of January 2009 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.