MD80 autoplt departs assigned altitude while accelerating to performance climb speed.

Attributes
ACN	436790
Time
Date	199905
Day	Thu
Local Time Of Day	1801 To 2400
Place
Locale Reference	navaid : ttt.vor
State Reference	TX
Altitude	msl single value : 10000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : d10.tracon
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	cruise : level
Route In Use	departure sid : dall5.ttt
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : multi engine pilot : instrument
ASRS Report	436790
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance non adherence : far
Independent Detector	atc equipment other atc equipment : radar other controllera other flight crewa other flight crewb
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

We were level at 10000 ft on the dall 5 departure after taking off runway 35L. Captain was flying. Heading 100 degrees to intercept the TTT 074 degree radial. Autoplt on in performance mode. Aircraft was accelerating to performance speed of 319 KTS. Aircraft started to climb out of 10000 ft. Captain disconnected autoplt and returned to 10000 ft. No TCASII warning, but we did get the controller's attention. This is the second time I've seen performance climb when accelerating at 10000 ft. Recommend not using performance until up to climb speed and above 10000 ft.

Original NASA ASRS Text

Title: MD80 AUTOPLT DEPARTS ASSIGNED ALT WHILE ACCELERATING TO PERFORMANCE CLB SPD.

Narrative: WE WERE LEVEL AT 10000 FT ON THE DALL 5 DEP AFTER TAKING OFF RWY 35L. CAPT WAS FLYING. HDG 100 DEGS TO INTERCEPT THE TTT 074 DEG RADIAL. AUTOPLT ON IN PERFORMANCE MODE. ACFT WAS ACCELERATING TO PERFORMANCE SPD OF 319 KTS. ACFT STARTED TO CLB OUT OF 10000 FT. CAPT DISCONNECTED AUTOPLT AND RETURNED TO 10000 FT. NO TCASII WARNING, BUT WE DID GET THE CTLR'S ATTN. THIS IS THE SECOND TIME I'VE SEEN PERFORMANCE CLB WHEN ACCELERATING AT 10000 FT. RECOMMEND NOT USING PERFORMANCE UNTIL UP TO CLB SPD AND ABOVE 10000 FT.

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.