Narrative:

We had lost hydraulic fluid in our right system and were just finishing up with the procedures prior to returning to dtw. The first officer had been flying and I had done the procedures. I had just taken the aircraft back so the first officer could free-fall the gear as we were descending to 6000'. The first officer asked me about the hydraulic quantity gauge and I looked away long enough to descend 400' below our assigned altitude. ATC said no problem, or conflict. They were aware of our problem and had been vectoring us around so we could troubleshoot the system. I should have used the autoplt and told the first officer to wait a min until we were leveled off on autoplt. Just goes to show even when you are trying to make sure someone is minding the store you still have to fly the aircraft first.

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Original NASA ASRS Text

Title: ACR MLG ALT DEVIATION OVERSHOT DURING DESCENT. FLT CREW WAS RETURNING TO DTW AFTER LOSING HYDRAULIC PRESSURE ON CLIMBOUT.

Narrative: WE HAD LOST HYD FLUID IN OUR RIGHT SYS AND WERE JUST FINISHING UP WITH THE PROCS PRIOR TO RETURNING TO DTW. THE F/O HAD BEEN FLYING AND I HAD DONE THE PROCS. I HAD JUST TAKEN THE ACFT BACK SO THE F/O COULD FREE-FALL THE GEAR AS WE WERE DSNDING TO 6000'. THE F/O ASKED ME ABOUT THE HYD QUANTITY GAUGE AND I LOOKED AWAY LONG ENOUGH TO DSND 400' BELOW OUR ASSIGNED ALT. ATC SAID NO PROB, OR CONFLICT. THEY WERE AWARE OF OUR PROB AND HAD BEEN VECTORING US AROUND SO WE COULD TROUBLESHOOT THE SYS. I SHOULD HAVE USED THE AUTOPLT AND TOLD THE F/O TO WAIT A MIN UNTIL WE WERE LEVELED OFF ON AUTOPLT. JUST GOES TO SHOW EVEN WHEN YOU ARE TRYING TO MAKE SURE SOMEONE IS MINDING THE STORE YOU STILL HAVE TO FLY THE ACFT FIRST.

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.