Date: 201904
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Airliner 99
Operator: Air Taxi
Operating under: Part 135
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Descent
Airspace: Class E ZZZ
Aircraft component: Oil Pressure Indication
Component problem: Failed
Reporter organization: Air Taxi
Reporter function: Captain; Single Pilot; Pilot Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Human factors: Workload; Training / Qualification; Time Pressure; Troubleshooting
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem; General Maintenance Action
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

Narrative: I was flying [a] Beech 99 to ZZZ. 35 miles north of ZZZ; Air Traffic Control cleared me from 6000 feet to 4000 feet. Just at that time I smelled burning electrical. Immediately without hesitation I radioed ATC that Flight XXXX smells smoke in the cockpit and is immediately turning off the electrical system and will be off air for a few minutes until I could evaluate the situation. ATC acknowledged. At this time I saw thick black smoke rising up from behind the pilot's instrument panel. I was on an IFR flight plan but was in VMC conditions; so I shut off the battery; generators; lights; inverter; stall heat; etc.; etc. As soon as I shut off everything; the smoke stopped rising from the panel. As the smoke started to clear; I turned on the battery; waited; generators; waited; and kept one radio on and one transponder. No smoke seemed to start back up. I told ATC I was back online and reported the situation. They wanted a detailed explanation of what my situation was. They also asked if I was declaring an emergency or needed fire rescue; and; or if I wanted to divert the flight to ZZZ1. I told them the situation was cleared and isolated with everything off; no smoke; and that I indeed had Runway XX in sight at ZZZ. I felt the flight could continue safely. They cleared me for the visual and I landed. Once parked; I wrote up the discrepancy and called it in to Maintenance. The next morning Maintenance reported nothing was found and signed off the aircraft for flight; which I then refused to fly. I wrote up the aircraft again stating I was not comfortable flying it for reason there was something indeed electrically burned the previous night. I received a phone call later that day stating they had found a canon plug burned on the left oil pressure gauge. This is an unfortunate situation how the aircraft had to be written up twice to have Maintenance dig deeper to find the problem. Somebody didn't do their proper job the first time around on the inspection. I should not have to be here writing this report to justify my professional judgement for safely flying the ship; to protect myself; for the lack of maintenance on their part.




Synopsis: Beech 99 Pilot reported experiencing smoke in the cockpit prior to landing at destination.