Altitude deviation. Descent through assigned altitude.

Attributes
ACN	281977
Time
Date	199409
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : tul
State Reference	OK
Altitude	msl bound lower : 9500 msl bound upper : 10000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	arrival other arrival star : star enroute airway : tul
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 240 flight time total : 16000 flight time type : 240
ASRS Report	281977
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 240 flight time total : 10000 flight time type : 900
ASRS Report	282727
Events
Anomaly	altitude deviation : overshoot non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other controllera other flight crewa
Resolutory Action	flight crew : became reoriented flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Descending to 10000 as cleared aircraft was on autoplt and descending 3500 FPM out of approximately 11500 ft MSL. At about 10700 ft MSL, captain attempted to slow descent rate at exact same time autoplt switched to altitude capture mode: which triggered the pitch mode default. We both saw the problem and I suggested the altitude hold mode which captain then engaged. While passing through 10000 ft captain changed more again which caused default to pitch mode again. Aircraft continued to descend at approximately 2000 FPM and, while passing 9800 ft, autoplt was disconnected and altitude trend reversed at 9500 ft MSL.there was no conflict with other traffic and the controller just verified our assigned altitude. In fact he cleared us to 9000 ft before asking. Problem arose with attempted mode change on autoplt, and altitude deviation occurred. Contributing factors: 1) descent intentionally started late to save fuel. 2) high descent rate used 3500 FPM and 420 KIAS. 3) both pilots horizontal distraction. 4) bad timing on mode change by captain (both times). 5) unconventional autoplt -- (in my opinion). 6) fatigue.

Original NASA ASRS Text

Title: ALTDEV. DSCNT THROUGH ASSIGNED ALT.

Narrative: DSNDING TO 10000 AS CLRED ACFT WAS ON AUTOPLT AND DSNDING 3500 FPM OUT OF APPROX 11500 FT MSL. AT ABOUT 10700 FT MSL, CAPT ATTEMPTED TO SLOW DSCNT RATE AT EXACT SAME TIME AUTOPLT SWITCHED TO ALT CAPTURE MODE: WHICH TRIGGERED THE PITCH MODE DEFAULT. WE BOTH SAW THE PROB AND I SUGGESTED THE ALT HOLD MODE WHICH CAPT THEN ENGAGED. WHILE PASSING THROUGH 10000 FT CAPT CHANGED MORE AGAIN WHICH CAUSED DEFAULT TO PITCH MODE AGAIN. ACFT CONTINUED TO DSND AT APPROX 2000 FPM AND, WHILE PASSING 9800 FT, AUTOPLT WAS DISCONNECTED AND ALT TREND REVERSED AT 9500 FT MSL.THERE WAS NO CONFLICT WITH OTHER TFC AND THE CTLR JUST VERIFIED OUR ASSIGNED ALT. IN FACT HE CLRED US TO 9000 FT BEFORE ASKING. PROB AROSE WITH ATTEMPTED MODE CHANGE ON AUTOPLT, AND ALT DEV OCCURRED. CONTRIBUTING FACTORS: 1) DSCNT INTENTIONALLY STARTED LATE TO SAVE FUEL. 2) HIGH DSCNT RATE USED 3500 FPM AND 420 KIAS. 3) BOTH PLTS HORIZ DISTR. 4) BAD TIMING ON MODE CHANGE BY CAPT (BOTH TIMES). 5) UNCONVENTIONAL AUTOPLT -- (IN MY OPINION). 6) FATIGUE.

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.