Narrative:

We were enroute on a part 135 charter flight; in level flight; at 14;000 ft; with the autopilot on. I was the pilot flying. Center cleared us to climb to 16;000 ft. My co-pilot set 16;000 ft in the altitude window; and I selected vertical speed on the autopilot mode select panel; to initiate the climb. I then looked down at my ipad to review a question I had about the expected instrument approach we were expecting at our destination. After about 10-15 seconds; I looked up to monitor the climb; and noticed that we were in a descent. I immediately disconnected the autopilot; and entered a rapid climb to the cleared altitude of 16;000 ft. The altitude loss was approximately 800 ft; before I initiated the correction. At 15;000 ft; the controller asked us to state our altitude. My co-pilot responded; '15;000 climbing to 16;000 ft.' no other comments were made by the controller.I do not know why the autopilot descended the aircraft. I have never experienced an event such as this; on this type aircraft. I am not aware of any input I may have made to cause the aircraft to descend; instead of climb. Regardless of what caused it to happen; I accept the fact; that if I had been properly monitoring the climb; rather than reviewing the approach; I would have realized the problem before an altitude deviation occurred. It is clear that I should have transferred the controls to the co-pilot; if I wanted to review the approach plate. Crew coordination; and procedural discipline; are of paramount importance; during all flight regimes. The controller did not mention if any conflict existed with any other aircraft during our altitude deviation.

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Original NASA ASRS Text

Title: The Captain of a Beechjet reported an altitude excursion during a climb on autopilot. While distracted reviewing the expected approach; the crew did not notice that the aircraft was descending rather than climbing.

Narrative: We were enroute on a Part 135 Charter flight; in level flight; at 14;000 ft; with the autopilot on. I was the Pilot Flying. Center cleared us to climb to 16;000 ft. My co-pilot set 16;000 ft in the altitude window; and I selected vertical speed on the autopilot mode select panel; to initiate the climb. I then looked down at my iPad to review a question I had about the expected instrument approach we were expecting at our destination. After about 10-15 seconds; I looked up to monitor the climb; and noticed that we were in a descent. I immediately disconnected the autopilot; and entered a rapid climb to the cleared altitude of 16;000 ft. The altitude loss was approximately 800 ft; before I initiated the correction. At 15;000 ft; the controller asked us to state our altitude. My co-pilot responded; '15;000 climbing to 16;000 ft.' No other comments were made by the controller.I do not know why the autopilot descended the aircraft. I have never experienced an event such as this; on this type aircraft. I am not aware of any input I may have made to cause the aircraft to descend; instead of climb. Regardless of what caused it to happen; I accept the fact; that if I had been properly monitoring the climb; rather than reviewing the approach; I would have realized the problem before an altitude deviation occurred. It is clear that I should have transferred the controls to the Co-pilot; if I wanted to review the approach plate. Crew coordination; and procedural discipline; are of paramount importance; during all flight regimes. The controller did not mention if any conflict existed with any other aircraft during our altitude deviation.

Data retrieved from NASA's ASRS site 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.