Light transport first officer climbed the aircraft to 12000 ft when he was to descend to 10000 ft.

Attributes
ACN	415960
Time
Date	199810
Day	Sun
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : byp
State Reference	TX
Altitude	msl bound lower : 11000 msl bound upper : 12000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zfw
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	descent other
Route In Use	arrival other arrival star : star
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : commercial pilot : atp
Experience	flight time last 90 days : 150 flight time total : 9600 flight time type : 150
ASRS Report	415960
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Was in a descent to dfw on the bonham arrival. We leveled at 11000 ft and I decided to use the restroom before we got busy. I went to the restroom and came back. I was getting buckled in and putting on my head set and heard the controller call and ask if we were at 12000 ft. We were just leveling off at 12000 ft. I said yes. He said 'I told you to descend to 10000 ft.' I looked at my first officer and asked him what is going on. He told me he thought he was told to climb to 12000 ft. The controller then told us to maintain 12000 ft and nothing more was said. My first officer misunderstood and climbed when he should have descended. Unfortunately, I was not there to catch the mistake. The only factor that I can see that may have caused this (other than my being in the restroom) would have been fatigue. We were on the last day of a 3-DAY trip and had been dealing with thunderstorms and delays for 2 days and we were both tired. Unfortunately it may have caused a deviation.

Original NASA ASRS Text

Title: LTT FO CLBED THE ACFT TO 12000 FT WHEN HE WAS TO DSND TO 10000 FT.

Narrative: WAS IN A DSCNT TO DFW ON THE BONHAM ARR. WE LEVELED AT 11000 FT AND I DECIDED TO USE THE RESTROOM BEFORE WE GOT BUSY. I WENT TO THE RESTROOM AND CAME BACK. I WAS GETTING BUCKLED IN AND PUTTING ON MY HEAD SET AND HEARD THE CTLR CALL AND ASK IF WE WERE AT 12000 FT. WE WERE JUST LEVELING OFF AT 12000 FT. I SAID YES. HE SAID 'I TOLD YOU TO DSND TO 10000 FT.' I LOOKED AT MY FO AND ASKED HIM WHAT IS GOING ON. HE TOLD ME HE THOUGHT HE WAS TOLD TO CLB TO 12000 FT. THE CTLR THEN TOLD US TO MAINTAIN 12000 FT AND NOTHING MORE WAS SAID. MY FO MISUNDERSTOOD AND CLBED WHEN HE SHOULD HAVE DSNDED. UNFORTUNATELY, I WAS NOT THERE TO CATCH THE MISTAKE. THE ONLY FACTOR THAT I CAN SEE THAT MAY HAVE CAUSED THIS (OTHER THAN MY BEING IN THE RESTROOM) WOULD HAVE BEEN FATIGUE. WE WERE ON THE LAST DAY OF A 3-DAY TRIP AND HAD BEEN DEALING WITH TSTMS AND DELAYS FOR 2 DAYS AND WE WERE BOTH TIRED. UNFORTUNATELY IT MAY HAVE CAUSED A DEV.

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.