Narrative:

En route from fxe to mlb ATC instructed us to descend from FL230 to FL200. The autoplt was inoperative and my copilot was PF. After descending and re-established in straight and level flight, I decided to use some time to become more familiar with the GPS. This was only my third flight in this aircraft and in this type aircraft and I was inexperienced with the model GPS on board. After approximately a min or so of playing with the GPS, ATC called and said 'say altitude.' I observed the vsi showing a descent and the altimeter approaching 19500 ft. The PF made the same observation and immediately began to correct. I think this deviation resulted from a combination of inattention, inexperience, and to a lesser extent, faulty autoplt and altitude alert system. My copilot is very inexperienced with only 320 total flight hours. I took this fact into consideration throughout the flight but since he had already been on the controls for about 1 hour and the aircraft was established in straight and level flight at 20000 ft, I saw no particular reason for concern while I focused my attention on the GPS for a few mins. I was unaware of my copilot's preoccupation with my activities and the breakdown in his own scan until we were queried by ATC. That is because the gradual descent gave no physical sensation that the aircraft was descending, there was no warning from the altitude alerter, and the deviation itself transpired over the course of a short time. In retrospect, I wish the autoplt had been working. I wish my copilot had paid more attention to his primary responsibility of flying the plane instead of what I was doing, and I wish I had paid more attention to my primary responsibility of flying the copilot. Opportunities to learn the GPS are limited on the ground due to heat and ground power requirements but I could have done a better job by giving clear CRM guidance prior to diverting my attention from operating the aircraft.

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Original NASA ASRS Text

Title: AN SW3 FLT CREW DEVIATE FROM ASSIGNED ALT.

Narrative: ENRTE FROM FXE TO MLB ATC INSTRUCTED US TO DSND FROM FL230 TO FL200. THE AUTOPLT WAS INOP AND MY COPLT WAS PF. AFTER DSNDING AND RE-ESTABLISHED IN STRAIGHT AND LEVEL FLT, I DECIDED TO USE SOME TIME TO BECOME MORE FAMILIAR WITH THE GPS. THIS WAS ONLY MY THIRD FLT IN THIS ACFT AND IN THIS TYPE ACFT AND I WAS INEXPERIENCED WITH THE MODEL GPS ON BOARD. AFTER APPROX A MIN OR SO OF PLAYING WITH THE GPS, ATC CALLED AND SAID 'SAY ALT.' I OBSERVED THE VSI SHOWING A DSCNT AND THE ALTIMETER APCHING 19500 FT. THE PF MADE THE SAME OBSERVATION AND IMMEDIATELY BEGAN TO CORRECT. I THINK THIS DEV RESULTED FROM A COMBINATION OF INATTENTION, INEXPERIENCE, AND TO A LESSER EXTENT, FAULTY AUTOPLT AND ALT ALERT SYS. MY COPLT IS VERY INEXPERIENCED WITH ONLY 320 TOTAL FLT HRS. I TOOK THIS FACT INTO CONSIDERATION THROUGHOUT THE FLT BUT SINCE HE HAD ALREADY BEEN ON THE CTLS FOR ABOUT 1 HR AND THE ACFT WAS ESTABLISHED IN STRAIGHT AND LEVEL FLT AT 20000 FT, I SAW NO PARTICULAR REASON FOR CONCERN WHILE I FOCUSED MY ATTN ON THE GPS FOR A FEW MINS. I WAS UNAWARE OF MY COPLT'S PREOCCUPATION WITH MY ACTIVITIES AND THE BREAKDOWN IN HIS OWN SCAN UNTIL WE WERE QUERIED BY ATC. THAT IS BECAUSE THE GRADUAL DSCNT GAVE NO PHYSICAL SENSATION THAT THE ACFT WAS DSNDING, THERE WAS NO WARNING FROM THE ALT ALERTER, AND THE DEV ITSELF TRANSPIRED OVER THE COURSE OF A SHORT TIME. IN RETROSPECT, I WISH THE AUTOPLT HAD BEEN WORKING. I WISH MY COPLT HAD PAID MORE ATTN TO HIS PRIMARY RESPONSIBILITY OF FLYING THE PLANE INSTEAD OF WHAT I WAS DOING, AND I WISH I HAD PAID MORE ATTN TO MY PRIMARY RESPONSIBILITY OF FLYING THE COPLT. OPPORTUNITIES TO LEARN THE GPS ARE LIMITED ON THE GND DUE TO HEAT AND GND PWR REQUIREMENTS BUT I COULD HAVE DONE A BETTER JOB BY GIVING CLR CRM GUIDANCE PRIOR TO DIVERTING MY ATTN FROM OPERATING THE ACFT.

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.