Narrative:

While on a descent to 8000 ft we were handed off from one controller to another. At the same time we were accomplishing items on the in-range checklist. I was the PF, and I inadvertently descended below 8000 ft. Upon noticing this, I quickly returned to altitude of 8000 ft. Before landing, approach control asked us to call the tower (or ATC) supervisor on duty. I contacted this individual and he stated that their equipment alarm went off to show inadequate vertical separation between us and another aircraft. On our return flight, we did an operational check with the same approach facility of our encoding altimeters. One system appeared to be off by 150- 200 ft and the aircraft was subsequently written up for altimeter discrepancy. Contributing factors to a poor level off of altitude were trying to accomplish a checklist in a descent, aircraft is not equipped with autoplt or a flight director with altitude capture capability, and fatigue due to many flight segments/long hours, this was leg 25 out of 26 in a 4 day period.

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Original NASA ASRS Text

Title: CAPT OF AN LTT OVERSHOT DSCNT ALT RESULTING IN LOSS OF STANDARD SEPARATION WITH OTHER TFC.

Narrative: WHILE ON A DSCNT TO 8000 FT WE WERE HANDED OFF FROM ONE CTLR TO ANOTHER. AT THE SAME TIME WE WERE ACCOMPLISHING ITEMS ON THE IN-RANGE CHKLIST. I WAS THE PF, AND I INADVERTENTLY DSNDED BELOW 8000 FT. UPON NOTICING THIS, I QUICKLY RETURNED TO ALT OF 8000 FT. BEFORE LNDG, APCH CTL ASKED US TO CALL THE TWR (OR ATC) SUPVR ON DUTY. I CONTACTED THIS INDIVIDUAL AND HE STATED THAT THEIR EQUIP ALARM WENT OFF TO SHOW INADEQUATE VERT SEPARATION BTWN US AND ANOTHER ACFT. ON OUR RETURN FLT, WE DID AN OPERATIONAL CHK WITH THE SAME APCH FACILITY OF OUR ENCODING ALTIMETERS. ONE SYS APPEARED TO BE OFF BY 150- 200 FT AND THE ACFT WAS SUBSEQUENTLY WRITTEN UP FOR ALTIMETER DISCREPANCY. CONTRIBUTING FACTORS TO A POOR LEVEL OFF OF ALT WERE TRYING TO ACCOMPLISH A CHKLIST IN A DSCNT, ACFT IS NOT EQUIPPED WITH AUTOPLT OR A FLT DIRECTOR WITH ALT CAPTURE CAPABILITY, AND FATIGUE DUE TO MANY FLT SEGMENTS/LONG HRS, THIS WAS LEG 25 OUT OF 26 IN A 4 DAY PERIOD.

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.