Narrative:

This incident happened on flight from bwi to gatwick. Departure was delayed more than 2 hours, due to late aircraft arrival and slow baggage loading. Area departure was uneventful and we were cleared to FL290 on flight planned route to ZDC. Climbing through FL220 the captain had to go to the bathroom. Shortly after he left the cockpit I was given a vector about 40 degrees left of course. As I was leveling at FL290 we were cleared to FL310. The autoplt had captured FL290 but the plane had not yet leveled off. I spun the altitude selector up and engaged flight level change to get it climbing again, intending to fine tune the altitude selector to FL310. I was then given another heading change, and then a traffic advisory. The traffic was at 3 O'clock and the controller explained that my vector were aimed at positioning me behind him. Shortly thereafter the controller asked me what altitude I had been cleared to. I immediately checked my altitude and saw that I was level at FL321 which was where the altitude selector had stopped when I spun it up to resume climb. I had been distracted before I got a chance to fine tune it to FL310. I immediately began a descent FL310 and acknowledged to the controller that that was my assigned altitude. Just then the captain knocked on the door. I let him in and told him what had happened.

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Original NASA ASRS Text

Title: FO OF ACR WDB CLIMBING OUT OF BWI ENROUTE TO GATWICK OVERSHOOTS ASSIGNED ALT OF 31000' BY OVER 1000' WHILE CAPT WAS OUT OF THE COCKPIT.

Narrative: THIS INCIDENT HAPPENED ON FLT FROM BWI TO GATWICK. DEP WAS DELAYED MORE THAN 2 HRS, DUE TO LATE ACFT ARR AND SLOW BAGGAGE LOADING. AREA DEP WAS UNEVENTFUL AND WE WERE CLRED TO FL290 ON FLT PLANNED RTE TO ZDC. CLBING THROUGH FL220 THE CAPT HAD TO GO TO THE BATHROOM. SHORTLY AFTER HE LEFT THE COCKPIT I WAS GIVEN A VECTOR ABOUT 40 DEGS LEFT OF COURSE. AS I WAS LEVELING AT FL290 WE WERE CLRED TO FL310. THE AUTOPLT HAD CAPTURED FL290 BUT THE PLANE HAD NOT YET LEVELED OFF. I SPUN THE ALT SELECTOR UP AND ENGAGED FLT LEVEL CHANGE TO GET IT CLBING AGAIN, INTENDING TO FINE TUNE THE ALT SELECTOR TO FL310. I WAS THEN GIVEN ANOTHER HDG CHANGE, AND THEN A TFC ADVISORY. THE TFC WAS AT 3 O'CLOCK AND THE CTLR EXPLAINED THAT MY VECTOR WERE AIMED AT POSITIONING ME BEHIND HIM. SHORTLY THEREAFTER THE CTLR ASKED ME WHAT ALT I HAD BEEN CLRED TO. I IMMEDIATELY CHKED MY ALT AND SAW THAT I WAS LEVEL AT FL321 WHICH WAS WHERE THE ALT SELECTOR HAD STOPPED WHEN I SPUN IT UP TO RESUME CLB. I HAD BEEN DISTRACTED BEFORE I GOT A CHANCE TO FINE TUNE IT TO FL310. I IMMEDIATELY BEGAN A DSNT FL310 AND ACKNOWLEDGED TO THE CTLR THAT THAT WAS MY ASSIGNED ALT. JUST THEN THE CAPT KNOCKED ON THE DOOR. I LET HIM IN AND TOLD HIM WHAT HAD HAPPENED.

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.