Narrative:

The aircraft was being vectored for an ILS approach into bdl. We were level at 7000' on a vector heading. The controller gave us a descent to 5000', which we acknowledged. The first officer, who is captain-rated and was PF, started a descent. I became preoccupied with selecting the ILS frequency on the #1 navigation radio (captain's) and did not check the aircraft's altitude. When I looked up, we were approximately 4300' and descending. As I started to check the altitude, the controller said, 'XXX, your assigned altitude is 5000', climb to 5000' immediately.' the first officer immediately initiated a climb to 5000' and the remainder of the approach was normal. The aircraft landed uneventfully. Fatigue was the factor affecting this particular crew, and a primary cause of the incident. Being the first sequence of flts after a week off, and after all 3 crew members had flown commercially into our base, we were exhausted. This was also an extra section added onto our regular scheduled trip. I had been awake for 26 hours, and the other 2 crew members at least as long. We had been officially on duty 14 hours and had flown 4 hours at the time of the altitude incursion. 2 contributing factors were firstly, the difficulty I was having with the #1 VHF navigation receiver not channelizing properly, thus prohibiting the captain from receiving the ILS signals. The second was the pointer type of altimeter which is difficult to read under any conditions.

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Original NASA ASRS Text

Title: FLT CREW OF ACR LGT DESCENDS TO 4300' INSTEAD OF THE 5000' TO WHICH THEY WERE CLEARED.

Narrative: THE ACFT WAS BEING VECTORED FOR AN ILS APCH INTO BDL. WE WERE LEVEL AT 7000' ON A VECTOR HDG. THE CTLR GAVE US A DSNT TO 5000', WHICH WE ACKNOWLEDGED. THE F/O, WHO IS CAPT-RATED AND WAS PF, STARTED A DSNT. I BECAME PREOCCUPIED WITH SELECTING THE ILS FREQ ON THE #1 NAV RADIO (CAPT'S) AND DID NOT CHK THE ACFT'S ALT. WHEN I LOOKED UP, WE WERE APPROX 4300' AND DSNDING. AS I STARTED TO CHK THE ALT, THE CTLR SAID, 'XXX, YOUR ASSIGNED ALT IS 5000', CLB TO 5000' IMMEDIATELY.' THE F/O IMMEDIATELY INITIATED A CLB TO 5000' AND THE REMAINDER OF THE APCH WAS NORMAL. THE ACFT LANDED UNEVENTFULLY. FATIGUE WAS THE FACTOR AFFECTING THIS PARTICULAR CREW, AND A PRIMARY CAUSE OF THE INCIDENT. BEING THE FIRST SEQUENCE OF FLTS AFTER A WK OFF, AND AFTER ALL 3 CREW MEMBERS HAD FLOWN COMMERCIALLY INTO OUR BASE, WE WERE EXHAUSTED. THIS WAS ALSO AN EXTRA SECTION ADDED ONTO OUR REGULAR SCHEDULED TRIP. I HAD BEEN AWAKE FOR 26 HRS, AND THE OTHER 2 CREW MEMBERS AT LEAST AS LONG. WE HAD BEEN OFFICIALLY ON DUTY 14 HRS AND HAD FLOWN 4 HRS AT THE TIME OF THE ALT INCURSION. 2 CONTRIBUTING FACTORS WERE FIRSTLY, THE DIFFICULTY I WAS HAVING WITH THE #1 VHF NAV RECEIVER NOT CHANNELIZING PROPERLY, THUS PROHIBITING THE CAPT FROM RECEIVING THE ILS SIGNALS. THE SECOND WAS THE POINTER TYPE OF ALTIMETER WHICH IS DIFFICULT TO READ UNDER ANY CONDITIONS.

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.