ALTDEV; AUTOPLT DID NOT CAPTURE.

Narrative

THE FLT BEING OPERATED WAS FROM DCA TO JFK. DEP WAS FROM RWY 03 AT DCA; WITH INITIAL ALT ASSIGNMENT OF 2000 FT MSL. THE FO WAS PF. AFTER DCA TWR HANDED US OFF TO WASHINGTON DEP; WE WERE CLRED TO 4000 FT. THE FO THEN ENGAGED THE AUTOPLT. AS PNF; I COMPLETED THE AFTER TKOF CHKLIST AND NOTICED NUMEROUS TARGETS BEING DISPLAYED ON THE TCASII. I GLANCED AT MY ALTIMETER AND NOTICED THAT WE WERE ABOUT TO LEVEL AT 4000 FT; AND THAT BOTH CAPT AND FO FLT DIRECTORS WERE INDICATING 'ALT CAPTURE.' SATISFIED THAT THE ACFT WAS LEVELING AT 4000 FT; I TURNED MY ATTN OUTSIDE THE COCKPIT TO SCAN FOR TFC IN OUR AREA. SHORTLY; THEREAFTER; I SCANNED MY ALTIMETER AND NOTICED WE WERE CLBING THROUGH 4400 FT MSL. I THEN GRABBED THE YOKE; DISCONNECTED THE AUTOPLT; AND NOSED THE ACFT OVER TO DSND BACK TO 4000 FT. WHILE EXECUTING THIS MANEUVER; WASHINGTON DEP CONTACTED US AND CLRED US TO CLB AND MAINTAIN 9000 FT MSL. THE CTLR MADE NO MENTION ABOUT THE ALTDEV OR ABOUT ANY PROB WITH LOSS OF SEPARATION. THE FO WAS UNAWARE OF THE DEV UNTIL I TOOK PHYSICAL CTL OF THE ACFT AND STATED THE NATURE OF THE PROB. I FEEL THAT THE FLT DIRECTOR/AUTOPLT SYS HAS A DESIGN FLAW THAT CAUSES SUCH OCCURRENCES. DURING THE 'ALT CAPTURE' PHASE; ANY MOVEMENT OF THE AUTOPLT PITCH WHEEL WILL DISARM THE CAPTURE MODE; ALLOWING THE ACFT TO CLB/DSND THROUGH THE PRESELECTED (DESIRED) ALT. WHILE THERE IS A SMALL AMBER LIGHT ON THE ALTIMETERS TO WARN OF AN OVERSHOOT/UNDERSHOOT; THERE IS NO AURAL WARNING. A DIFFERENT ACFT TYPE IN OUR FLEET DOES HAVE AN AURAL WARNING FEATURE. THE OPERATING PROC TAUGHT BY OUR COMPANY IS TO CLB/DSND IN THE 'BASIC' OR 'PITCH WHEEL' MODE. PITCH ATTITUDE IS CTLED BY MOVEMENT OF THE AUTOPLT PITCH WHEEL. THIS MODE IS USED PRIMARILY FOR PAX COMFORT; AS THE AUTOPLT 'CHASES' THE IAS AND VERT SPD MODES. PLT TECHNIQUE CAN AGGRAVATE THE PROB AS WELL. WHEN APCHING A DESIRED ALT; SOME PLTS HAVE AN UNCONSCIOUS HABIT OF DECREASING THE RATE OF CLB/DSCNT WITH THE AUTOPLT PITCH WHEEL; OFTEN WHILE THE FLT DIRECTOR IS CAPTURING. AS STATED BEFORE; THIS CAUSES THE ALT CAPTURE MODE TO DISARM; SETTING THE SCENE FOR AN ALT DEV. THIS 'TRAP' IS NOT MENTIONED IN THE COMPANY ISSUED ACFT MANUALS OR ADDRESSED IN THE TRAINING PROGRAM. UNLESS WARNED; MOST PLTS LEARN BY 'TRIAL AND ERROR.' HUMAN FACTORS: THE MOST OBVIOUS 'HUMAN FACTORS' ERROR IS RELYING ON THE AUTOPLT WITHOUT PROPERLY MONITORING IT. THAT FACT THAT BOTH PLTS MISSED THE OVERSHOOT SUGGESTS A CERTAIN AMOUNT OF COMPLACENCY WITH THE EQUIP. THE FACT THAT THE FO; AS PF; WAS COMPLETELY UNAWARE OF THE DEV LEADS ME TO BELIEVE SHE HAD A LAPSE OF CONCENTRATION. IN THE PAST; SHE HAS PROVEN TO BE A SHARP; COMPETENT FO. PERHAPS I BECAME COMPLACENT WITH HER PERFORMANCE AND DIDN'T MONITOR THE ACFT AS CLOSELY AS I SHOULD HAVE. TO PREVENT A RECURRENCE: 1) BE AWARE OF EQUIP/HUMAN SHORTCOMINGS. 2) DISCIPLINE THYSELF TO MONITOR ALL LEVEL OFFS AND FO'S.