Light Transport; High Wing; 2 Turboprop Eng
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Aircraft Equipment Problem Dissipated; Flight Crew Landed in Emergency Condition; Flight Crew Overcame Equipment Problem; General Maintenance Action
Aircraft
Just prior to the top of descent I sensed a smoky odor in the cockpit. After a brief monitor of the sensation; the phenomena increased in intensity. I asked the First Officer to confirm the presence of smoke; which he confirmed. At that point; as a precaution I commanded the First Officer that we don oxygen masks and request ATC for a descent to 12;000 [feet] to prepare for corrective action in the event that the event became fully abnormal. The First Officer communicated to ATC that we required an immediate descent due to the presence of smoke in the cockpit. ATC cleared us initially to 16;000 [feet]; then shortly after; to 12;000 feet. Subsequently; we were to become aware that ATC advised for us. Descending through 16;000 feet; we observed that the smoke didn't appear to intensify. I asked the First Officer to remove his mask to assess the cockpit environment. After all appeared clear; we removed our oxygen masks and proceeded to run through the smoke abnormal checklist. From that point to landing; we monitored the situation and attempted to troubleshoot the source of the smoke. At the conclusion I contacted the Chief Pilot; Maintenance and Dispatch to describe our circumstances. A maintenance write up was entered in the Aircraft Flight Maintenance Log. A Mechanic was dispatched to our location and after performing an inspection; returned the aircraft to service. Oxygen mask lenses should be cleaned or checked for hazing. It was very difficult to effectively observe cockpit instruments and switches because the mask lens was extremely hazed or dusty.
Just prior to planned top of descent from 32;000 [feet]; Captain indicated he smelt and saw smoke in the cabin. Emergency memory items for smoke in cockpit were immediately performed and O2 masks were placed on; O2 mask microphone was activated; and ATC was advised we had smoke in the cockpit. Lowest possible sector altitude was requested and a descent was begun to 12;000 [feet]. We continued to ZZZ in descent. ATC advised for us. At 16;000 feet I removed my mask as I did not see smoke. The Captain removed his mask shortly thereafter. I performed QRH checklist items for SMOKE and smoke/burnt smell evident in the cockpit. O2 masks - Don; o2 mask mike - activate; ZZZ was nearest suitable; seatbelt/no smoking switches to On; RECIRC-EFIS-AVIONIC FAN - Off. Spoke to Flight Attendant and asks if she had smoke in passenger compartment - she did not. Continued with checklist for smoke/burnt smell evident in flight compartment. MAN CAB ALT sector - turn gradually to UP (Captain instructed me not to do this). We suspected BLEED source and I proceeded to AIR CONDITION SMOKE REMOVAL on QRH EMERG -18. SMOKE procedure was completed and continued with smoke/burnt smell primarily entering the flight compartment.  RH ECS BLEED - OFF; X-BLEED - On; EMERGENCY DESCENT was being performed. We continued descent and flight path to ZZZ as nearest suitable and performed a visual approach and landed on RWY XX at ZZZ with out needing to perform a ground evacuation.
Air carrier flight crew reported a fumes event accompanied with smoke at top of descent and continued to a landing at destination.