An appeal against a ruling that the black box from a helicopter which crashed off Shetland should be given to Scotland's top prosecutor has been abandoned.

The British Airline Pilots' Association (Balpa) said it has decided not to proceed with the legal move, which would have seen the case return to court in December.

The Super Puma was carrying 16 passengers and two crew from the Borgsten Dolphin platform when it crashed into the sea on its approach to Sumburgh Airport.

Three men and one woman were killed in the accident on August 23 2013.

The Air Accidents Investigation Branch (AAIB) began an immediate investigation into the crash which is now thought to be well advanced.

The Lord Advocate, Frank Mulholland QC, previously went to the Court of Session in Edinburgh to ask for the black box - a combined voice and flight data recorder known as a CVFDR - to be made available to him and Police Scotland.

Prosecutors had asked the AAIB to make the recorder available to them for use in their investigations but it refused to do so in the absence of an order from the court.

Judge Lord Jones ruled in June that the black box should be made available.

Balpa, which opposed the Lord Advocate's move, initially planned to appeal against the ruling but has now decided not to proceed.

A Crown Office spokesman said: "The Crown can advise that the British Airline Pilots' Association have abandoned their appeal at the Court of Session.

"The families of those who lost their lives in the tragedy have been advised of this and will continue to be updated in relation to any other significant developments.

"The investigation into the circumstances of the crash that resulted in the deaths continues."

Confirming its decision, Balpa said pilots remain "deeply concerned about the safety implications of this unprecedented legal intervention by the Crown in an ongoing safety investigation".

It added: "Given that in this case the AAIB has now completed the substantive part of its investigation and issued its draft report to interested parties for comment, Balpa will no longer contest the court's ruling that limited cockpit voice recorder and flight data recorder data may be released early to the Lord Advocate.

"The court imposed sensible conditions which mean analysis may only be undertaken under strict confidentiality and important non-disclosure and redaction caveats must also be observed."

Those who died in the crash were Duncan Munro, from Bishop Auckland, Co Durham; George Allison, from Winchester, Hampshire; Sarah Darnley, from Elgin, Moray; and Gary McCrossan, from Inverness.