CHALLENGER CL604 FLT CREW HAS AN ALT DEV DURING TEB5 DEP.

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ON THE TEB5 DEP WITH AUTOPLT AND AUTOTHROTTLES ENGAGED; THE FLAPS WERE RAISED AND A SHORT TIME AFTER THE ALTITUDE CAPTURED AT 1500 FT. I NOTICED THE ACFT TURNING R TOWARDS HDG 280 DEGS; THE PITCH DECREASED AND THE AUTOTHROTTLES PULLED BACK. I WAS LOOKING OUTSIDE FOR TFC I SAW ON TCAS BEFORE AND FOLLOWED THE FREQ CHANGE OF THE FO FROM TOWER TO DEP. THE NEXT THING WE HEARD WAS THE ALTITUDE WARNING AS THE ACFT CLBED THROUGH 1800 FT. THE ALTITUDE MODE STILL SHOWED ALT CAPTURED. I DESELECTED THE AUTOPLT AND STARTED DESCENDING TOWARDS 1500 FT BUT AT THE SAME TIME DEP CLRED US TO 6000 FT. WE THINK THE MAXIMUM ALTITUDE WAS AROUND 1850 FT BUT THE DATA WILL HAVE TO BE VERIFIED THROUGH FLT DATA MONITORING. IT IS STANDARD PROC OF OUR OPERATION TO RAISE THE FLAPS WHEN PASSING THE TAKEOFF SAFETY SPEED VFTO. WE FOLLOWED THIS SOP BUT BECAUSE OF THE NOISE ABATEMENT PROC AT TEB WE REACHED VFTO LATER THAN USUAL. LEVEL OFF; HEADING CHANGE AND A CHANGE IN CONFIGURATION AT THE SAME TIME WAS MORE THAN AUTOMATION WAS ABLE TO COPE WITH. THE LESSON LEARNED: IN A SIMILAR SITUATION I WOULD DELAY THE CONFIGURATION CHANGE IN ORDER TO GIVE THE AUTOMATION SYSTEM ENOUGH TIME TO REACT OR FLY IN A MODE OF LESS AUTOMATION.