Narrative:

Approach cleared us to descend from 5000' to 3000'; descending through 4000' the descent checklist was initiated. The non-flying pilot (first officer) challenged, and I was responding, to the checklist items. During this phase our attention was diverted to cockpit tasks, and thus our outside scan was interrupted. Within 15 seconds of leveling at 3000' an small aircraft appeared from our 3:30 position at approximately the same altitude. I initiated evasive action (descent and turn to the right) and we passed within a few hundred feet of the small aircraft. I believe the primary cause of the near-miss was reduced vigilance outside the cockpit while dealing with the distraction of the required checklist. The approach controller never called the traffic out to us - probably because he himself was very busy with IFR traffic and providing radar advisories to numerous VFR aircraft. I feel safer flying on a low IFR day, when all the small aircraft's are on the ground. This incident reinforces my resolve to keep an eye outside during/while 'checks' are in progress inside the cockpit.

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Original NASA ASRS Text

Title: LTT AND SMA HAVE NMAC.

Narrative: APCH CLRED US TO DESCEND FROM 5000' TO 3000'; DESCENDING THROUGH 4000' THE DESCENT CHECKLIST WAS INITIATED. THE NON-FLYING PLT (F/O) CHALLENGED, AND I WAS RESPONDING, TO THE CHECKLIST ITEMS. DURING THIS PHASE OUR ATTN WAS DIVERTED TO COCKPIT TASKS, AND THUS OUR OUTSIDE SCAN WAS INTERRUPTED. WITHIN 15 SECONDS OF LEVELING AT 3000' AN SMA APPEARED FROM OUR 3:30 POSITION AT APPROX THE SAME ALT. I INITIATED EVASIVE ACTION (DESCENT AND TURN TO THE RIGHT) AND WE PASSED WITHIN A FEW HUNDRED FEET OF THE SMA. I BELIEVE THE PRIMARY CAUSE OF THE NEAR-MISS WAS REDUCED VIGILANCE OUTSIDE THE COCKPIT WHILE DEALING WITH THE DISTR OF THE REQUIRED CHECKLIST. THE APCH CTLR NEVER CALLED THE TFC OUT TO US - PROBABLY BECAUSE HE HIMSELF WAS VERY BUSY WITH IFR TFC AND PROVIDING RADAR ADVISORIES TO NUMEROUS VFR ACFT. I FEEL SAFER FLYING ON A LOW IFR DAY, WHEN ALL THE SMA'S ARE ON THE GND. THIS INCIDENT REINFORCES MY RESOLVE TO KEEP AN EYE OUTSIDE DURING/WHILE 'CHECKS' ARE IN PROGRESS INSIDE THE COCKPIT.

Data retrieved from NASA's ASRS site as of August 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.