South Korea's Air Force on Saturday refuted allegations that air traffic control played any role in the crash of a fire department helicopter that left all five crew members dead.

The Eurocopter-built AS365 Dauphin medium-weight helicopter crashed Thursday in a residential area of Gwangju, 329 kilometers south of Seoul. The chopper and its crew were returning to a base in Gangwon Province after taking part in search missions related to the April 16 sinking of the Sewol ferry off the country's southwestern coast that left more than 300 people dead or missing.

The Air Force said its controllers only give clearance on altitude to aircraft flying in military-controlled airspace.

"Reaching a designated altitude is carried out at the discretion of the pilots and various other factors such as the performance of the aircraft," it said in a press release.

There have been questions raised by some critics that military air traffic controllers did not tell the pilots of the ill-fated flight to "ascend slowly" to the flight altitude they dictated.

While transcripts of the communication between the pilots and air traffic controllers have not been released, the Air Force said all data has been sent to the Ministry of Land, Infrastructure and Transport's Aviation and Railway Accident Investigation Board, which is heading the probe. All other Dauphin helicopters in South Korea have been grounded pending the results of the investigation.

Related to the accident, local experts have pointed out that photos of the doomed helicopter showed it in a very steep nose-down position as it plummeted to the earth, and there was no sign of the "autorotation" maneuver that all pilots train for to reduce the descent rate. The emergency move makes use of air moving through the helicopter's main rotors to give pilots who have lost engine power the ability to glide the aircraft to a landing area.

Because of a fire after the crash, the black boxes on the chopper have been seriously damaged, which may require them to be sent to the manufacturer in France in order to recover crucial data, investigators said. This they said could take several months. (Yonhap)