Smoke that filled the cabin of a Delta flight as it took off from the Atlanta airport in February was so thick the lead flight attendant had trouble seeing past the first row of passengers and the pilots donned oxygen masks as a precaution.

The National Transportation Safety Board released the preliminary report for a Delta Air Lines flight from Atlanta to Charleston that had to be evacuated after smoke filled the cabin.

No oil was visible in the gauge on the right engine’s oil reservoir after a February Delta Air Lines flight filled with smoke during takeoff at Atlanta’s Hartsfield Jackson International Airport, a preliminary report from the National Transportation Safety Board said Wednesday.