Altitude deviation excursion from assigned altitude.

Attributes
ACN	147159
Time
Date	199005
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : zma
State Reference	FL
Altitude	msl bound lower : 38100 msl bound upper : 39000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zma
Operator	general aviation : corporate
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Route In Use	enroute : other oceanic
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : cfi pilot : atp pilot : instrument pilot : commercial
Experience	flight time last 90 days : 70 flight time total : 8400 flight time type : 2000
ASRS Report	147159
Person 2
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other controllera other flight crewa
Resolutory Action	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:

Cruising enroute, FL390, from st maarten in the carribean to fort lauderdale, fl, the autoplt disconnected and the airplane rolled to the left and started to descend. We lost about 900' before I pulled the airplane back up to altitude. It happened just after I returned from a visit to the toilet and climbed into the seat. I don't know if I hit the switch getting in the seat or if it was hit by the coplts clipboard that he dropped on the console just after I sat down. I climbed into the seat strapped in and put on my headset and then looked at the instruments and noticed the descending turn. It only took about 15-20 seconds but that's all it takes. As I was pulling the airplane back up center called and asked our altitude. By the time the copilot answered center, we were level at FL390. Some things to note: the autoplt does not have an audible disconnect warning. Although the switch is a large paddle and makes some noise when it flips to the off position. After the incident, we tried the switch manually and it was easier than most to move from on to off. The altitude alerter warning avoid was very low and could not be heard west/O the headset on because of the way the switching works. I'm not sure why the copilot didn't hear it but my getting back in the seat may have distraction him. The important things to learn from this are that you must pay close attention to the airplane at all times. The electronic and autoflt system that allow you to relax also make uou complacent about what's happening with the airplane.

Original NASA ASRS Text

Title: ALT DEVIATION EXCURSION FROM ASSIGNED ALT.

Narrative: CRUISING ENROUTE, FL390, FROM ST MAARTEN IN THE CARRIBEAN TO FORT LAUDERDALE, FL, THE AUTOPLT DISCONNECTED AND THE AIRPLANE ROLLED TO THE L AND STARTED TO DSND. WE LOST ABOUT 900' BEFORE I PULLED THE AIRPLANE BACK UP TO ALT. IT HAPPENED JUST AFTER I RETURNED FROM A VISIT TO THE TOILET AND CLBED INTO THE SEAT. I DON'T KNOW IF I HIT THE SWITCH GETTING IN THE SEAT OR IF IT WAS HIT BY THE COPLTS CLIPBOARD THAT HE DROPPED ON THE CONSOLE JUST AFTER I SAT DOWN. I CLBED INTO THE SEAT STRAPPED IN AND PUT ON MY HEADSET AND THEN LOOKED AT THE INSTRUMENTS AND NOTICED THE DSNDING TURN. IT ONLY TOOK ABOUT 15-20 SECS BUT THAT'S ALL IT TAKES. AS I WAS PULLING THE AIRPLANE BACK UP CTR CALLED AND ASKED OUR ALT. BY THE TIME THE COPLT ANSWERED CTR, WE WERE LEVEL AT FL390. SOME THINGS TO NOTE: THE AUTOPLT DOES NOT HAVE AN AUDIBLE DISCONNECT WARNING. ALTHOUGH THE SWITCH IS A LARGE PADDLE AND MAKES SOME NOISE WHEN IT FLIPS TO THE OFF POS. AFTER THE INCIDENT, WE TRIED THE SWITCH MANUALLY AND IT WAS EASIER THAN MOST TO MOVE FROM ON TO OFF. THE ALT ALERTER WARNING AVOID WAS VERY LOW AND COULD NOT BE HEARD W/O THE HEADSET ON BECAUSE OF THE WAY THE SWITCHING WORKS. I'M NOT SURE WHY THE COPLT DIDN'T HEAR IT BUT MY GETTING BACK IN THE SEAT MAY HAVE DISTR HIM. THE IMPORTANT THINGS TO LEARN FROM THIS ARE THAT YOU MUST PAY CLOSE ATTN TO THE AIRPLANE AT ALL TIMES. THE ELECTRONIC AND AUTOFLT SYS THAT ALLOW YOU TO RELAX ALSO MAKE UOU COMPLACENT ABOUT WHAT'S HAPPENING WITH THE AIRPLANE.

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.