B737-200 FLC IS GIVEN XING RESTR AND FO IS INTERRUPTED WHEN TUNING THE FREQ. HE NEGLECTS TO ADD THE LAST DIGIT AND THEY DO NOT DSND; MISSING THE XING RESTR.

Narrative

THE ACFT WAS INBOUND TO DCA FROM EWR ON V378 BTWN MODENA VOR AND BALTIMORE. CTR CLRED FLT TO CROSS 15 MI N OF BAL VOR AT 12000 FT. THE CAPT WAS FLYING THE ACFT AND ASKED THE FO TO DIAL IN BAL VOR ON THE #2 NAV UNIT AS THE CAPT WAS NAVING WITH THE #1 SELECTED TO MODENA. APPROX 60 DME INDICATING ON THE #2 NAV UNIT; ATC ASKED WHEN WE WERE GOING TO BEGIN OUR DSCNT TO MAKE THE XING RESTR. THE ACFT WAS CRUISING AT FL200 AND WITH ONLY 8000 FT TO LOSE WE COMPUTED OUR DSCNT POINT TO BE 40 DME OUT FROM BALTIMORE. WE REPLIED 'IN ANOTHER 15 MI OR SO' WE WOULD BEGIN OUR DSCNT; FURTHER STATING WE SHOWED OURSELVES TO BE 60 MI FROM BALTIMORE. CTR QUICKLY CAME BACK AND STATED 'I SHOW YOU WITH ONLY ABOUT 15 MI TO MAKE YOUR DSCNT.' THE FO HAD PUT 115.0 INTO THE NAV UNIT INSTEAD OF 115.1 WHICH WAS THE FREQ FOR BAL. WHEN I HAD ASKED THE FO TO PUT IN THE BAL VOR FREQ; A RADIO CALL CAME IN AND INTERRUPTED HIM CAUSING HIM TO NOT COMPLETELY FINISH PUTTING IN THE PROPER FREQ. I SHOULD HAVE BEEN MONITORING MORE CLOSELY; BUT WAS INVOLVED IN FLYING THE ACFT AS OUR AUTOPLT WAS INOP. WE MISSED OUR XING RESTR BY 4 MI NOT GETTING LEVEL UNTIL 11 MI; INSTEAD OF THE ORIGINALLY CLRED 15 MI. ATC STATED 'THERE WAS NO CONFLICT' AND DIDN'T REALLY HAVE A PROB WITH WHAT WE DID.