Disconnect autoplt and did not notice slow climb versus descent.

Attributes
ACN	170993
Time
Date	199102
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : bsy
State Reference	FL
Altitude	msl bound lower : 31000 msl bound upper : 31800
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zma
Operator	common carrier : air carrier
Make Model Name	Heavy Transport, Low Wing, 4 Turbojet Eng
Navigation In Use	Other
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 150 flight time total : 6500 flight time type : 1000
ASRS Report	170993
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Aircraft was dispatched with autoplt inoperative and crew had to hand-fly. Crew had been on duty for 14 hours and was quite fatigued. Cruise altitude of FL310 was requested instead of flight plan altitude of FL390 in order to make the aircraft easier to control. Autoplt was engaged, even though placarded as inoperative because partial advantage could be accomplished; i.e., autoplt behaved as though in 'control wheel steering,' or in effect dampened out inputs, but still required constant hands-on monitoring.. At approximately XA38Z, 86 mi southeast of biscayne VOR on the 124 degree right, descend was initiated and descent checklist called for. Autoplt was placed off. As responses were being given to checklist and while being hampered by looking into the late afternoon sun it was discovered that when the autoplt was released a descent had not begun, but instead the aircraft had begun a shallow undetected climb to approximately FL318. No warning was received from altitude alert system because cleared lower altitude of 16000'. Had already been selected immediate descent was begun and no comment received from ATC and no traffic conflict noted.

Original NASA ASRS Text

Title: DISCONNECT AUTOPLT AND DID NOT NOTICE SLOW CLIMB VERSUS DESCENT.

Narrative: ACFT WAS DISPATCHED WITH AUTOPLT INOP AND CREW HAD TO HAND-FLY. CREW HAD BEEN ON DUTY FOR 14 HRS AND WAS QUITE FATIGUED. CRUISE ALT OF FL310 WAS REQUESTED INSTEAD OF FLT PLAN ALT OF FL390 IN ORDER TO MAKE THE ACFT EASIER TO CTL. AUTOPLT WAS ENGAGED, EVEN THOUGH PLACARDED AS INOP BECAUSE PARTIAL ADVANTAGE COULD BE ACCOMPLISHED; I.E., AUTOPLT BEHAVED AS THOUGH IN 'CTL WHEEL STEERING,' OR IN EFFECT DAMPENED OUT INPUTS, BUT STILL REQUIRED CONSTANT HANDS-ON MONITORING.. AT APPROX XA38Z, 86 MI SE OF BISCAYNE VOR ON THE 124 DEG R, DSND WAS INITIATED AND DSNT CHKLIST CALLED FOR. AUTOPLT WAS PLACED OFF. AS RESPONSES WERE BEING GIVEN TO CHKLIST AND WHILE BEING HAMPERED BY LOOKING INTO THE LATE AFTERNOON SUN IT WAS DISCOVERED THAT WHEN THE AUTOPLT WAS RELEASED A DSNT HAD NOT BEGUN, BUT INSTEAD THE ACFT HAD BEGUN A SHALLOW UNDETECTED CLB TO APPROX FL318. NO WARNING WAS RECEIVED FROM ALT ALERT SYS BECAUSE CLRED LOWER ALT OF 16000'. HAD ALREADY BEEN SELECTED IMMEDIATE DSNT WAS BEGUN AND NO COMMENT RECEIVED FROM ATC AND NO TFC CONFLICT NOTED.

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.