AN appeal has been lodged to block the release of black box recordings from a fatal helicopter crash off Shetland.

Pilots' union Balpa says releasing the information from the cockpit voice recorder before the Air Accidents Investigation Branch (AAIB) has completed its investigation "cuts across everything pilots and the broader flight safety community stand for".

It comes after a Scotland's top law officer, Lord Advocate Frank Mulholland QC, won his bid to the data released.

Prosecutors have been trying to establish whether anybody could be held criminally responsible for the crash.

In a controversial move, Judge Lord Jones, at the Court of Session in Edinburgh, ruled in June that disclosing the black box data from the Sumburgh crash was "both in the public interest and in the interests of justice".

The AAIB, which belongs to the UK Department for Transport, is not normally obliged to hand over black box data to external bodies.

Four offshore workers died when their Super Puma helicopter ditched around two miles west of Sumburgh airport in August 2013.

An interim report from the AAIB found that pilot error may have been to blame, but a final report on the tragedy is expected later this year.

Jim McAuslan, General Secretary of BALPA, said: "The 2013 Super Puma accident was tragic, and it is vital the AAIB gets to the root cause and has access to whatever data it needs.

"However, providing the data to the prosecutor and the police in parallel to the AAIB's investigation cuts across everything pilots and the broader flight safety community stand for. We cannot stand by while the court allows that to happen without pursuing other legal avenues to highlight our concerns and question whether it is the correct approach."

He added: "Pilots are concerned the open safety culture it has taken decades to create, would be threatened if safety data is used to assign blame without air accident investigation specialists being given the time, space and resources to carry out their work fully."