Air carrier flight crew reported while in cruise flight noticing a strong acrid smell and smoke in the flight deck resulting in the flight crew returning to the departure airport.
Synopsis
Air carrier flight crew reported while in cruise flight noticing a strong acrid smell and smoke in the flight deck resulting in the flight crew returning to the departure airport.
Narrative
We were in cruise at 330 when the Captain and I first smelled something. Neither of us could identify what it was or where it was coming from. He suggested it smelled similar to Ozone but neither of us could be sure. I had my window shades up but when I took them down; we could both clearly see smoke through the sunlight. It appeared to be primarily coming from my side of the aircraft. We looked around and tried to identify a source but couldn't. I think it was about this time when I suggested we don oxygen masks and pulled out the smoke; fire; fumes checklist. However; even in that short time of recognizing the smoke and finding the appropriate checklist; the smoke dissipated. I went to the galley (we were a ferry flight so there were no FA's (Flight Attendants) to ask) and looked for any indications of smoke or fumes back there. It seemed totally normal so the issue was definitely more concentrated up front. We discussed the options: continue to ZZZ1 and have the issue possibly come back over the mountains; or divert back to ZZZ. We agreed that the safest option was to head back. I told ATC we needed to go back and they gave us a vector. I got the box set up for a diversion and notified the company of our situation. We originally didn't don our masks because the smoke dissipated so quickly but after several minutes the Captain mentioned not feeling very well so we both decided to put them on. At this point; communication got much more difficult but still manageable. We used the interphone when necessary but also relied on nonverbal communication (pointing; thumbs up etc). Even though it was harder to communicate; I feel like we were on the same page with everything throughout the flight. Once or twice I would hop on to ask if he was comfortable and feeling good; at which point he said yes and we kept going. It was a pretty routine flight once we turned back to ZZZ. They cleared us to ZZZ; then a fix on the ILS XXR and we went in for a normal landing.
Second reporter narrative
We were ferrying an aircraft to ZZZ1. Shortly after reaching cruise altitude we noticed a strong acrid smell. Within seconds we could see a thin white smoke. we could not determine where the smoke was coming from. We performed the emergency procedure by donning O2 masks and running the emergency checklist. We [requested priority handling] with ATC and quickly returned to ZZZ.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.