Narrative:

During flight from ZZZ to ZZZ1 at 9;000 feet MSL in IMC conditions with the autopilot engaged and being vectored by TRACON. The pfd indicated the aircraft was rolling to the left approximately 35-40 degrees pitching down approximately 7-10 degrees and the airspeed was increasing; I simultaneously rolled the aircraft level; reduced the thrust levers and disengaged the autopilot as airspeed decreased I began raising the nose to a level attitude and increasing thrust continuing to pitch up to climb attitude upon regaining the assigned altitude. I assured the crew that the situation was under control. ATC continued to provide vectors to avoid areas of moderate to heavy precipitation allowing me to proceed direct to the IAF. While proceeding direct to the IAF I made 2 unsuccessful attempts to re-engage the autopilot.I advised the crew to prepare for landing completed the descent checklist and was cleared for the approach. With the aircraft established on the approach and approaching the glide slope I extended approach flaps; lowered the landing gear and while performing the landing checklist observed the nose gear down indication was not illuminated. I pressed to test the light and it illuminated. I notified ATC that I was executing a missed approach and proceed according to ATC instructions. Once established at the assigned altitude; I queried ATC concerning the weather conditions at ZZZ2 while I considered diverting there. As I awaited the response I cycled the landing gear down the nose gear down indication failed to illuminate. ATC indicated that ZZZ2 was indicating 1500 overcast. Prior to requesting a clearance to ZZZ2 I once again cycled the landing gear handle down and observed all three gear down indicator lights illuminated. I requested and received a clearance to proceed direct to the RNAV GPS runway xx IAF and proceed to execute the approach which terminated with an uneventful landing and taxied to the ramp. Inadvertent autopilot disconnect; failure of autopilot alarm to notify pilot of disconnect and pilots diverted attention to programming the navigation system for the approach. Thorough diagnosis of autopilot to determine cause of inadvertent disconnect and repair is required.

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Original NASA ASRS Text

Title: BE90 Captain reported autopilot failure caused a diversion.

Narrative: During flight from ZZZ to ZZZ1 at 9;000 feet MSL in IMC conditions with the Autopilot engaged and being vectored by TRACON. The PFD indicated the aircraft was rolling to the left approximately 35-40 degrees pitching down approximately 7-10 Degrees and the airspeed was increasing; I simultaneously rolled the aircraft level; reduced the thrust levers and disengaged the autopilot as airspeed decreased I began raising the nose to a level attitude and increasing thrust continuing to pitch up to Climb Attitude Upon regaining the assigned altitude. I assured the crew that the situation was under control. ATC continued to provide vectors to avoid areas of moderate to heavy precipitation allowing me to proceed direct to the IAF. While proceeding direct to the IAF I made 2 unsuccessful attempts to re-engage the autopilot.I advised the crew to prepare for landing completed the Descent Checklist and was cleared for the approach. with the aircraft established on the approach and approaching the glide slope I extended Approach Flaps; lowered the Landing Gear and while performing the Landing Checklist observed The Nose Gear Down Indication was not illuminated. I pressed to test the light and it illuminated. I notified ATC that I was executing a missed approach and proceed according to ATC instructions. Once established at the assigned altitude; I queried ATC concerning the weather conditions at ZZZ2 while I considered diverting there. As I awaited the response I cycled the Landing Gear down the Nose Gear Down Indication Failed to Illuminate. ATC indicated that ZZZ2 was indicating 1500 Overcast. Prior to requesting a clearance to ZZZ2 I once again cycled the Landing Gear Handle down and observed all three Gear Down Indicator Lights Illuminated. I requested and received a clearance to proceed direct to the RNAV GPS Runway XX IAF and proceed to execute the approach which terminated with an uneventful landing and taxied to the ramp. Inadvertent Autopilot disconnect; Failure of Autopilot Alarm to notify pilot of disconnect and pilots diverted attention to programming the Navigation System for the approach. Thorough diagnosis of Autopilot to determine cause of Inadvertent Disconnect and repair is required.

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.