Beechjet 400
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Flight Engineer
Flight Crew Last 90 Days 125; Flight Crew Total 18000; Flight Crew Type 4000
Distraction; Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Flight Deck / Cabin / Aircraft Event Other / Unknown
Air Traffic Control Provided Assistance; Flight Crew Overcame Equipment Problem; Flight Crew Returned To Clearance; Flight Crew Became Reoriented
Human Factors; Aircraft
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.
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.