Narrative:

Captain (PF) asked for approach flaps setting of 15 degrees. We were at 4000 ft, on intercept vector for ILS, and cleared for approach. I set 15 degree flaps and noticed 'slat disagree' light. PF said, 'I've got aircraft and ATC, you get out the book.' automatic approach was selected at the time. I bent down to my book bag and got out the cockpit operating manual and tried to locate the procedure for this particular problem. Meanwhile, the PF told ATC of our problem and requested vectors off the approach so we could work the procedure. Immediately, ATC cancelled approach clearance and gave us a heading and told us to maintain 4000 ft. At about the same time the autoplt intercepted the localizer and the GS and started a descent. The PF turned to the heading ok, but failed to stop the descent. He was preoccupied with setting the power, because the automatic throttles had just clicked off when 15 degrees flaps was selected. When I looked up, we were about 400 ft low. I made some reference to the altitude at about the same time as ATC. We returned to level flight, and ran the malfunction procedure and landed uneventfully. Lessons learned: even when looking in the book, xchk the other pilot's flying performance. When flying automatic approachs, plan on failures of autoplt and automatic throttle at the worst possible time.

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Original NASA ASRS Text

Title: ALTDEV ALT EXCURSION DURING A GAR PROC.

Narrative: CAPT (PF) ASKED FOR APCH FLAPS SETTING OF 15 DEGS. WE WERE AT 4000 FT, ON INTERCEPT VECTOR FOR ILS, AND CLRED FOR APCH. I SET 15 DEG FLAPS AND NOTICED 'SLAT DISAGREE' LIGHT. PF SAID, 'I'VE GOT ACFT AND ATC, YOU GET OUT THE BOOK.' AUTO APCH WAS SELECTED AT THE TIME. I BENT DOWN TO MY BOOK BAG AND GOT OUT THE COCKPIT OPERATING MANUAL AND TRIED TO LOCATE THE PROC FOR THIS PARTICULAR PROB. MEANWHILE, THE PF TOLD ATC OF OUR PROB AND REQUESTED VECTORS OFF THE APCH SO WE COULD WORK THE PROC. IMMEDIATELY, ATC CANCELLED APCH CLRNC AND GAVE US A HDG AND TOLD US TO MAINTAIN 4000 FT. AT ABOUT THE SAME TIME THE AUTOPLT INTERCEPTED THE LOC AND THE GS AND STARTED A DSCNT. THE PF TURNED TO THE HDG OK, BUT FAILED TO STOP THE DSCNT. HE WAS PREOCCUPIED WITH SETTING THE PWR, BECAUSE THE AUTO THROTTLES HAD JUST CLICKED OFF WHEN 15 DEGS FLAPS WAS SELECTED. WHEN I LOOKED UP, WE WERE ABOUT 400 FT LOW. I MADE SOME REF TO THE ALT AT ABOUT THE SAME TIME AS ATC. WE RETURNED TO LEVEL FLT, AND RAN THE MALFUNCTION PROC AND LANDED UNEVENTFULLY. LESSONS LEARNED: EVEN WHEN LOOKING IN THE BOOK, XCHK THE OTHER PLT'S FLYING PERFORMANCE. WHEN FLYING AUTO APCHS, PLAN ON FAILURES OF AUTOPLT AND AUTO THROTTLE AT THE WORST POSSIBLE TIME.

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.