Narrative:

I was PIC on the aircraft, but was allowing the first officer to fly this leg. We were inbound to dallas-love field, approximately 30 mi east of scurry VOR, and had received a clearance to descend to 16000'. As we were nearing the altitude assigned, I tuned in ATIS to see if the information had changed. I was writing down the information when the altitude alerter sounded for the second time, indicating we were 300' off altitude (in this case, low). I immediately said 'pull up, you are too low!' he responded and said 'sorry, I was thinking 15000.' then center called and said 'light transport X, you are assigned 16000', say altitude.' I keyed the microphone and reported we were correcting out of 15900 for 16000.' then, before handing us off to approach on 119.05, center advised us that we had set off the 'dinger' and asked me to call. 2/mon/90, I called and was told the person assigned would call back. Later that day (name) called and we had a pleasant discussion on what had happened. She informed me we had gone as low as 15600' MSL, 400' below assigned altitude, and showed immediate correction. I told her the PF misunderstood the descent clearance, unbeknown to me, even though the correct altitude was set in the altitude alerter. I have learned, I hope, not to allow myself to be distracted nearing assigned altitudes. The PF in the right seat had flown for air carrier airlines for 22 yrs and had done a good job the previous flight engineer days in this aircraft with me. I have learned that that is no excuse to let my guard down,a nd also as PIC I should and will from now on minimize distrs while approaching newly assigned altitudes, also. I realize this is no way to be blamed on the first officer. I was PIC and accept full responsibility. I will also add that even though nothing has been mentioned about traffic by center, nor during my phone conversation, we saw and had in sight an aircraft going outbnd below us to our right with no concerns as to a posing problem. Supplemental information from acn 136489: I was back at 16000' when I noticed an aircraft that I spotted as earlier traffic pass off of my right 2-3 O'clock position, approximately 1000' below, but well clear horizontal. A few mins later ATC told us of the conflict and that we had set off the switch alarm.

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Original NASA ASRS Text

Title: ACFT DESCENDED BELOW ASSIGNED ALT AND CONFLICTED WITH IFR ACFT, RESULTING IN LESS THAN STANDARD SEPARATION.

Narrative: I WAS PIC ON THE ACFT, BUT WAS ALLOWING THE F/O TO FLY THIS LEG. WE WERE INBND TO DALLAS-LOVE FIELD, APPROX 30 MI E OF SCURRY VOR, AND HAD RECEIVED A CLRNC TO DSND TO 16000'. AS WE WERE NEARING THE ALT ASSIGNED, I TUNED IN ATIS TO SEE IF THE INFO HAD CHANGED. I WAS WRITING DOWN THE INFO WHEN THE ALT ALERTER SOUNDED FOR THE SECOND TIME, INDICATING WE WERE 300' OFF ALT (IN THIS CASE, LOW). I IMMEDIATELY SAID 'PULL UP, YOU ARE TOO LOW!' HE RESPONDED AND SAID 'SORRY, I WAS THINKING 15000.' THEN CENTER CALLED AND SAID 'LTT X, YOU ARE ASSIGNED 16000', SAY ALT.' I KEYED THE MIC AND RPTED WE WERE CORRECTING OUT OF 15900 FOR 16000.' THEN, BEFORE HANDING US OFF TO APCH ON 119.05, CENTER ADVISED US THAT WE HAD SET OFF THE 'DINGER' AND ASKED ME TO CALL. 2/MON/90, I CALLED AND WAS TOLD THE PERSON ASSIGNED WOULD CALL BACK. LATER THAT DAY (NAME) CALLED AND WE HAD A PLEASANT DISCUSSION ON WHAT HAD HAPPENED. SHE INFORMED ME WE HAD GONE AS LOW AS 15600' MSL, 400' BELOW ASSIGNED ALT, AND SHOWED IMMEDIATE CORRECTION. I TOLD HER THE PF MISUNDERSTOOD THE DSCNT CLRNC, UNBEKNOWN TO ME, EVEN THOUGH THE CORRECT ALT WAS SET IN THE ALT ALERTER. I HAVE LEARNED, I HOPE, NOT TO ALLOW MYSELF TO BE DISTRACTED NEARING ASSIGNED ALTS. THE PF IN THE RIGHT SEAT HAD FLOWN FOR ACR AIRLINES FOR 22 YRS AND HAD DONE A GOOD JOB THE PREVIOUS FE DAYS IN THIS ACFT WITH ME. I HAVE LEARNED THAT THAT IS NO EXCUSE TO LET MY GUARD DOWN,A ND ALSO AS PIC I SHOULD AND WILL FROM NOW ON MINIMIZE DISTRS WHILE APCHING NEWLY ASSIGNED ALTS, ALSO. I REALIZE THIS IS NO WAY TO BE BLAMED ON THE F/O. I WAS PIC AND ACCEPT FULL RESPONSIBILITY. I WILL ALSO ADD THAT EVEN THOUGH NOTHING HAS BEEN MENTIONED ABOUT TFC BY CENTER, NOR DURING MY PHONE CONVERSATION, WE SAW AND HAD IN SIGHT AN ACFT GOING OUTBND BELOW US TO OUR RIGHT WITH NO CONCERNS AS TO A POSING PROB. SUPPLEMENTAL INFO FROM ACN 136489: I WAS BACK AT 16000' WHEN I NOTICED AN ACFT THAT I SPOTTED AS EARLIER TFC PASS OFF OF MY RIGHT 2-3 O'CLOCK POS, APPROX 1000' BELOW, BUT WELL CLR HORIZ. A FEW MINS LATER ATC TOLD US OF THE CONFLICT AND THAT WE HAD SET OFF THE SWITCH ALARM.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.