THE CAPT OF A DC10-30 OVERSHOT ASSIGNED ALT DURING DEP CLB RESULTING IN A TCASII RA AND ATC REQUESTING HIS ALT. THE CAPT BECAME DISTR WITH A DISAGREEMENT BTWN THE 2 NAV RECEIVERS; WHICH AFFECTED THE 2 FLT DIRECTORS; AND FORGOT TO ARM THE AUTOPLT ALT CAPTURE.

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WE DEPARTED FROM EBRU (BRUSSELS; BELGIUM) WITHOUT A PROB. UPON PASSING 10000 FT; I CALLED IN TIMES TO HANDLING AND OBTAINED A SELCAL. JUST AS I FINISHED GETTING SELCAL THE; THE TCASII GAVE A TA; THEN SHORTLY AFTER; AN RA. THE CAPT PROMPTLY DISENGAGED THE AUTOPLT AND BEGAN TO DSND TO COMPLY WITH THE RA. BY THE TIME I TURNED MY SEAT AROUND TO LOOK FOR TFC WE WERE LEVELING AT 17000 FT AND THE TCASII SAID 'TFC NO FACTOR.' WHAT I BELIEVE HAD HAPPENED; WAS THE AUTOPLT FAILED TO CAPTURE AND; BEING AT A FAIRLY LIGHT WT; CLBED THROUGH OUR ASSIGNED ALT OF 17000 FT. THE CAPT CAUGHT THE PROB AND BEGAN THE CORRECTION AND SPOTTED THE TFC XING ON A NON COLLISION COURSE TO OUR R SIDE PASSING IN BACK OF US. SUPPLEMENTAL INFO FROM ACN 415123: THE ALT ARM FEATURE OF THE FMS HAD BECOME UNARMED (UPON ANALYSIS AFTER THE INCIDENT) AND I ALLOWED THE ACFT TO CLB TO 17300 FT PRIOR TO DISENGAGING THE AUTOPLT AND DSNDING BACK TO 17000 FT. THE ERROR ON MY PART RESULTED IN AN ULTIMATE ALTDEV OF 500 FT (17500 FT BY THE TIME I HAD DISCONNECTED THE AUTOPLT AND DSNDED THE ACFT).