A United Airlines DC8 cargo plane that crashed during takeoff from Detroit Jan. 11 was being piloted by a flight engineer not qualified to fly it, according to documents released by the National Transportation Safety Board.

The documents, which include a transcript of the cockpit voice recording, show that shortly before takeoff, the flight engineer, the "No. 3 man" in the cockpit, traded places with the copilot and assumed the controls, while the captain remained in his seat but took on the copilot's role.

The four-engine jet, carrying only the three crew members and cargo that included five pounds of low-level radioactive material, crashed about 30 seconds after an early-morning takeoff from Detroit Metropolitan Airport, killing the crew. The radioactive material was found intact in its lead package and posed no danger.

Documents made public Friday at the NTSB are "factual data" compiled by investigators and entered without analysis or conclusions. A final report indicating probable cause of the accident is not expected until summer, when more data is collected.

A United spokesman declined comment, other than to say that if a seat switch did occur in the cockpit, it would have violated Federal Aviation Administration regulations and United's policy.

The transcript at one point shows Captain William S. Todd saying, "Are you guys trading?" and moments later Flight Engineer Robert E. Lee, 50, saying, "Oh, we're trading now."

The exchanges from that point make it clear that Lee had assumed the pilot's role, Todd copilot and Copilot James G. Day the role of flight engineer.

According to the documents, Lee tried unsuccessfully to upgrade his status to pilot for a DC8 in 1979 but showed poor knowledge of procedures. He received pilot status for a twin-engine Boeing 737 in 1980, but it was revoked a year later when he failed to pass a flight test. The records show Lee then agreed with his superiors at United to remain a flight engineer for the balance of his career.

The data also hint at a possible cause of the crash: investigators found that the "trim" mechanism on the plane's horizontal tail, which determines the craft's pitch, was in a position that would have pitched the nose too high on takeoff, making the plane impossible to control.