Baron 58/58TC
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Private
Flight Crew Last 90 Days 50; Flight Crew Total 1100; Flight Crew Type 100
Distraction; Workload
Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance; Flight Crew Executed Go Around / Missed Approach; Flight Crew Overcame Equipment Problem; Flight Crew Regained Aircraft Control
Weather; Aircraft
On route to intercepting the localizer Runway 19 on the approach the door opened unexpectedly. The resulting sound; wind and general turbulence caused me to descend below the glideslope and generate a low altitude alarm at the control facility.Because the weather was at minimums and I was having trouble controlling the aircraft I elected to abort the approach and climb. ATC [gave] me instructions to higher altitudes which I had trouble maintaining due to the way the aircraft was performing with the door ajar and the fact that I was in IMC with turbulence.I was finally able to gain consistent control of the aircraft and ATC guided me to higher altitude outside of IMC and I was able (with ATC help) to get to [another airport] where I was able to land uneventfully. Throughout the entire process I had difficulty staying on altitude and being able to quickly reach assigned headings. At [the alternate airport] a 45 knot cross wind at altitude made it difficult to stay on the ILS; but I managed to stay within tolerances.I did not [request priority handling] because I felt I could handle the situation without doing that. I recognized the controllers had their hands full with the inclement weather and didn't want to further inconvenience them and other pilots.
The pilot of a BE58 experienced an unexpected opening of the cabin door on approach. A go-around and diversion was executed in instrument conditions with turbulence; where a successful landing was made.