The aircraft, which was carrying 199 passengers and six crew members, flew for around 10 minutes without a pilot in command of the plane, according to the report.
Lufthansa told dpa that it was aware of the investigation report and that its own flight safety department had also conducted an investigation. The company didn't disclose its results, dpa said.
Although the unconscious co-pilot apparently operated controls unintentionally, the aircraft was able to continue flying in a stable manner thanks to the active autopilot. During this time period, the voice recorder recorded strange noises in the cockpit that were consistent with an acute health emergency, dpa reported.
The captain initially tried entering the regular door opening code, which triggers a buzzer in the cockpit so that the co-pilot can open the door. He did so five times without being able to enter the cockpit. A stewardess tried to contact the co-pilot using the onboard telephone.
Finally, the captain typed in an emergency code that would have allowed him to open the door on his own. However, shortly before the door would have opened automatically, the co-pilot opened it from the inside despite being ill, dpa reported.
The pilot then decided to make an unplanned landing in Madrid, where his colleague was taken to a hospital.