Narrative:

We were given a heading to intercept the localizer by dulles approach and cleared from 9000 ft to 8000 ft and given a frequency change. We began descent to 8000 ft with autoplt engaged, began turn toward new assigned heading. Once bank was established, realizing the 1/2 bank mode was still on, I looked down to disengage it and became distracted with the steeper bank angle, changing frequency and setting up for localizer. During this time the altitude/sel function became disengaged, unnoticed by me. The captain was busy calling company and briefing passenger. He noticed the altitude deviation and instantly recovered. After his action, I realized what had happened. The controller asked us if we were on frequency yet and the captain responded. Through this I have adopted a more disciplined xchk and scan of altitude awareness, autoplt indications at all times, especially during altitude and heading transitions using the company procedure of 1000 ft, 500 ft calls in addition adding armed after 500 ft call and scanning for 300 ft, 200 ft, 100 ft, altitude/capture, altitude/on indications and rechk and scan procedure not allowing myself to become complacent and distracted. Callback conversation with reporter revealed the following information: the reporter flies the jetstream 4100 for a regional air carrier. The first officer is relatively low time in the aircraft. The first officer assumes full responsibility for the altitude deviation. He may have changed descent modes which would have knocked off the altitude capture feature of the autoplt. Dulles was giving a step-down descent with many 1000 ft changes. The altitude alerter was going off continuously. The captain was 'heavily involved' with company radio, ATIS, etc and was out of the loop. Reporter now is more aware of the traps in the autoplt.

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Original NASA ASRS Text

Title: ALT OVERSHOOT ON DSCNT.

Narrative: WE WERE GIVEN A HDG TO INTERCEPT THE LOC BY DULLES APCH AND CLRED FROM 9000 FT TO 8000 FT AND GIVEN A FREQ CHANGE. WE BEGAN DSCNT TO 8000 FT WITH AUTOPLT ENGAGED, BEGAN TURN TOWARD NEW ASSIGNED HDG. ONCE BANK WAS ESTABLISHED, REALIZING THE 1/2 BANK MODE WAS STILL ON, I LOOKED DOWN TO DISENGAGE IT AND BECAME DISTRACTED WITH THE STEEPER BANK ANGLE, CHANGING FREQ AND SETTING UP FOR LOC. DURING THIS TIME THE ALT/SEL FUNCTION BECAME DISENGAGED, UNNOTICED BY ME. THE CAPT WAS BUSY CALLING COMPANY AND BRIEFING PAX. HE NOTICED THE ALTDEV AND INSTANTLY RECOVERED. AFTER HIS ACTION, I REALIZED WHAT HAD HAPPENED. THE CTLR ASKED US IF WE WERE ON FREQ YET AND THE CAPT RESPONDED. THROUGH THIS I HAVE ADOPTED A MORE DISCIPLINED XCHK AND SCAN OF ALT AWARENESS, AUTOPLT INDICATIONS AT ALL TIMES, ESPECIALLY DURING ALT AND HDG TRANSITIONS USING THE COMPANY PROC OF 1000 FT, 500 FT CALLS IN ADDITION ADDING ARMED AFTER 500 FT CALL AND SCANNING FOR 300 FT, 200 FT, 100 FT, ALT/CAPTURE, ALT/ON INDICATIONS AND RECHK AND SCAN PROC NOT ALLOWING MYSELF TO BECOME COMPLACENT AND DISTRACTED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR FLIES THE JETSTREAM 4100 FOR A REGIONAL ACR. THE FO IS RELATIVELY LOW TIME IN THE ACFT. THE FO ASSUMES FULL RESPONSIBILITY FOR THE ALTDEV. HE MAY HAVE CHANGED DSCNT MODES WHICH WOULD HAVE KNOCKED OFF THE ALT CAPTURE FEATURE OF THE AUTOPLT. DULLES WAS GIVING A STEP-DOWN DSCNT WITH MANY 1000 FT CHANGES. THE ALT ALERTER WAS GOING OFF CONTINUOUSLY. THE CAPT WAS 'HEAVILY INVOLVED' WITH COMPANY RADIO, ATIS, ETC AND WAS OUT OF THE LOOP. RPTR NOW IS MORE AWARE OF THE TRAPS IN THE AUTOPLT.

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.