Widebody transport in cruise set FMS to climb from FL330 to FL350. Began descent to 3500' instead.

Attributes
ACN	85126
Time
Date	198804
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : grw
State Reference	MS
Altitude	msl bound lower : 32000 msl bound upper : 33000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zme
Operator	common carrier : air carrier
Make Model Name	Widebody, Low Wing, 3 Turbojet Eng
Navigation In Use	Other
Flight Phase	climbout : intermediate altitude cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : commercial pilot : atp
Experience	flight time last 90 days : 160 flight time total : 20000 flight time type : 3500
ASRS Report	85126
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Experience	flight time last 90 days : 198 flight time total : 12000 flight time type : 1000
ASRS Report	85182
Events
Anomaly	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:

We were in cruise at FL330 using FMS and autoplt. Mem center cleared us to FL350. I selected FL350 on the FMS and engaged VNAV. The first officer changed the altitude alert selector to 35000'. I was distracted for a few seconds and the first officer said we are descending. We were descending at approximately 1000 FPM. I disengaged the autoplt and put the aircraft in a climb to FL350. We lost approximately 1000' in this maneuver. Since we had unlimited visibility it was done smoothly. I advised the first officer to tell the mem center what we were doing, which he did. In checking to find the cause I found the FMS calling for 3500' instead of 35000'. Apparently the FMS didn't take a zero or it dropped out. Since the altitude alert selector was set for 35000', there was no 250' warning of leaving the altitude. The center probably didn't get an alert for the same reasons. I have been operating this equipment for over 7 yrs west/O any occurrence of this nature. I guess the lesson here is, don't be too complacent with this automatic navigation equipment. This is one situation where we don't have altitude alerting to warn us of a descent.

Original NASA ASRS Text

Title: WDB IN CRUISE SET FMS TO CLIMB FROM FL330 TO FL350. BEGAN DESCENT TO 3500' INSTEAD.

Narrative: WE WERE IN CRUISE AT FL330 USING FMS AND AUTOPLT. MEM CENTER CLRED US TO FL350. I SELECTED FL350 ON THE FMS AND ENGAGED VNAV. THE F/O CHANGED THE ALT ALERT SELECTOR TO 35000'. I WAS DISTRACTED FOR A FEW SECS AND THE F/O SAID WE ARE DSNDING. WE WERE DSNDING AT APPROX 1000 FPM. I DISENGAGED THE AUTOPLT AND PUT THE ACFT IN A CLB TO FL350. WE LOST APPROX 1000' IN THIS MANEUVER. SINCE WE HAD UNLIMITED VIS IT WAS DONE SMOOTHLY. I ADVISED THE F/O TO TELL THE MEM CENTER WHAT WE WERE DOING, WHICH HE DID. IN CHKING TO FIND THE CAUSE I FOUND THE FMS CALLING FOR 3500' INSTEAD OF 35000'. APPARENTLY THE FMS DIDN'T TAKE A ZERO OR IT DROPPED OUT. SINCE THE ALT ALERT SELECTOR WAS SET FOR 35000', THERE WAS NO 250' WARNING OF LEAVING THE ALT. THE CENTER PROBABLY DIDN'T GET AN ALERT FOR THE SAME REASONS. I HAVE BEEN OPERATING THIS EQUIP FOR OVER 7 YRS W/O ANY OCCURRENCE OF THIS NATURE. I GUESS THE LESSON HERE IS, DON'T BE TOO COMPLACENT WITH THIS AUTOMATIC NAV EQUIP. THIS IS ONE SITUATION WHERE WE DON'T HAVE ALT ALERTING TO WARN US OF A DSCNT.

Data retrieved from NASA's ASRS site as of August 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.