Investigators have recovered the cockpit voice recorder from the Navy airplane that crashed in the southeastern port city of Pohang, North Gyeongsang Province, killing all four crew members on board.

Military authorities said Friday that when the P-3C maritime patrol aircraft took off from a Pohang naval air base at 1:43 p.m. on Thursday for flight training, weather conditions were good, adding that they are looking into various possibilities to determine the cause of the crash, including a bird strike and engine issues.

The officers on board the plane were taking part in training drills to practice taking off and landing, during which they were to fly around the base and make contact with the runway three times.

After making its first contact with the runway, the plane took off for its second drill but crashed into a hillside near the base at 1:49 p.m.

Authorities also said the plane communicated with the control tower one minute before the crash and did not report an emergency.

Regarding eyewitness accounts that the plane suddenly turned around just before the crash, Navy officials said they believe the pilots may have been trying to maneuver the aircraft to prevent harm to people on the ground.

A joint memorial altar for the officers who died will be set up at the Pohang Naval Air Command gymnasium, and a funeral is set for Sunday at the command base.