Narrative:

New york approach cleared us to descend to 4000 ft MSL from our cruise altitude of 7000 ft MSL. The first officer, who was the PF, descended through our assigned altitude of 4000 ft MSL to 3000 ft MSL. Prior to the event, I informed the first officer that I would be off the primary frequency to make a required passenger briefing. When I returned to the primary frequency, I observed we were descending down to 3000 ft MSL. I questioned the first officer if new york approach cleared us to a lower altitude, he responded in doubt. At that time, new york approach asked us what altitude we were descending to. I replied we were at 3000 ft MSL, and asked the controller what altitude he wanted us at. He told us we were assigned 4000 ft MSL but just stay at 3000 ft MSL. Shortly after, we were switched to another new york approach controller. The altitude deviation did not result in any immediate actions to take place. No further incident. The operator has a fleet of 2 BAE3100 jetstreams. Both have no autoplt. Only one has an altitude alerter. For the sake of standardization with other aircraft, the alerter was not used. At the time of the event, we were on duty for 11 hours. Prior to the flight in question, we had an 8 hour 30 min layover (on duty) which required us to stay at the FBO facility. Supplemental information from acn 546540: I feel that this is a situation that is very easy to get into -- especially flying an extremely complex airplane single pilot without aid of an autoplt. This is a short flight in which we fly about 5 times a week, and the fact that one flight is a carbon copy of the last, one gets used to the same things time and again. Even though the controller said cleared to 4000 ft, I heard 3000 ft, the altitude given 99% of the time. I can prevent this by completing all descent checklist items before the descent. This way, both pilots can be watching the progress of the aircraft in such a critical phase of flight.

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Original NASA ASRS Text

Title: A JS31 CREW, ON DSCNT TO FRG, OVERSHOT THEIR ASSIGNED ALT.

Narrative: NEW YORK APCH CLRED US TO DSND TO 4000 FT MSL FROM OUR CRUISE ALT OF 7000 FT MSL. THE FO, WHO WAS THE PF, DSNDED THROUGH OUR ASSIGNED ALT OF 4000 FT MSL TO 3000 FT MSL. PRIOR TO THE EVENT, I INFORMED THE FO THAT I WOULD BE OFF THE PRIMARY FREQ TO MAKE A REQUIRED PAX BRIEFING. WHEN I RETURNED TO THE PRIMARY FREQ, I OBSERVED WE WERE DSNDING DOWN TO 3000 FT MSL. I QUESTIONED THE FO IF NEW YORK APCH CLRED US TO A LOWER ALT, HE RESPONDED IN DOUBT. AT THAT TIME, NEW YORK APCH ASKED US WHAT ALT WE WERE DSNDING TO. I REPLIED WE WERE AT 3000 FT MSL, AND ASKED THE CTLR WHAT ALT HE WANTED US AT. HE TOLD US WE WERE ASSIGNED 4000 FT MSL BUT JUST STAY AT 3000 FT MSL. SHORTLY AFTER, WE WERE SWITCHED TO ANOTHER NEW YORK APCH CTLR. THE ALTDEV DID NOT RESULT IN ANY IMMEDIATE ACTIONS TO TAKE PLACE. NO FURTHER INCIDENT. THE OPERATOR HAS A FLEET OF 2 BAE3100 JETSTREAMS. BOTH HAVE NO AUTOPLT. ONLY ONE HAS AN ALT ALERTER. FOR THE SAKE OF STANDARDIZATION WITH OTHER ACFT, THE ALERTER WAS NOT USED. AT THE TIME OF THE EVENT, WE WERE ON DUTY FOR 11 HRS. PRIOR TO THE FLT IN QUESTION, WE HAD AN 8 HR 30 MIN LAYOVER (ON DUTY) WHICH REQUIRED US TO STAY AT THE FBO FACILITY. SUPPLEMENTAL INFO FROM ACN 546540: I FEEL THAT THIS IS A SIT THAT IS VERY EASY TO GET INTO -- ESPECIALLY FLYING AN EXTREMELY COMPLEX AIRPLANE SINGLE PLT WITHOUT AID OF AN AUTOPLT. THIS IS A SHORT FLT IN WHICH WE FLY ABOUT 5 TIMES A WK, AND THE FACT THAT ONE FLT IS A CARBON COPY OF THE LAST, ONE GETS USED TO THE SAME THINGS TIME AND AGAIN. EVEN THOUGH THE CTLR SAID CLRED TO 4000 FT, I HEARD 3000 FT, THE ALT GIVEN 99% OF THE TIME. I CAN PREVENT THIS BY COMPLETING ALL DSCNT CHKLIST ITEMS BEFORE THE DSCNT. THIS WAY, BOTH PLTS CAN BE WATCHING THE PROGRESS OF THE ACFT IN SUCH A CRITICAL PHASE OF FLT.

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.