AN ACR B727 FLC DSNDS BELOW THE ASSIGNED ALT WHEN THE FO BECAME DISTRACTED BY THE TCASII'S TA AND LATER RECEIVES AN RA.

Narrative

WHILE BEING VECTORED TO FINAL (RWY 22; ORD) AND DSNDING TO 7000 FT MSL AND SLOWING TO 210 KIAS; WE RECEIVED A TA FROM THE TCASII. THIS ALERT REDIRECTED OUR ATTN OUTSIDE THE AIRPLANE DURING THE FINAL 200 FT TO LEVEL OFF. THE PROX OF THE ACFT COMBINED WITH OUR DSCNT RATE (PLUS THE CLB RATE OF THE OTHER ACFT) CAUSED THE TA TO BECOME AN RA. THIS DISTR DREW OUR ATTN COMPLETELY AWAY FROM THE LEVELOFF AT 7000 FT MSL. THE DEV WAS NOTED PASSING 6750 FT MSL AND IMMEDIATE PWR AND PITCH INCREASE WERE APPLIED. MAX ALTDEV 300 FT LOW (6700 FT MSL). THE ACFT TFC WAS SIGHTED JUST PRIOR TO THE DEV RECOGNITION. SAFETY WAS NOT AN ISSUE (IE; NEAR MISS) -- THE OTHER ACFT APPEARED TO BE APPROX 1 MI AWAY. ALTHOUGH TRAINING IN THE BACK SEAT (FE) WAS BEING CONDUCTED; THIS WAS NOT A CONTRIBUTING FACTOR. THIS WAS THE FIRST FLT OF THE DAY AFTER A 14 HR LAYOVER. REST/FATIGUE WAS ALSO NOT A FACTOR. THE COINCIDENTAL TA/RA AT LEVELOFF AND SPD REDUCTION REDIRECTED OUR ATTN AWAY FROM FLYING THE ACFT. SUPPLEMENTAL INFO FROM ACN 395471: APCHING 7000 FT WE GOT A TCASII RA TO 'MONITOR VERT DSCNT.' THE TCASII SCREEN INDICATED AN AIRPLANE ABOUT 2 MI IN FRONT OF US LEVEL AT 6000 FT. WHILE LOOKING AT THE SCREEN THE COPLT DSNDED BELOW 7000 FT AND THE RA CONTINUED. SEEING THAT THE COPLT WAS BELOW THE ASSIGNED ALT THE CAPT TOLD THE COPLT TO MAINTAIN 7000 FT. AT THE SAME TIME CHICAGO APCH CALLED AND STATED 'MAINTAIN 7000 FT.' THE CAPT REMARKED 'ROGER; MAINTAIN 7000 FT.' THE COPLT STOPPED THE DSCNT AND BOTTOMED OUT AT 6700 FT. HE QUICKLY CORRECTED THE ALT BACK TO 7000 FT.