The family of Lockerbie bomber Abdelbaset al-Megrahi will launch a bid to appeal against his conviction within a fortnight.
Lawyer Aamer Anwar confirmed files will be handed to the Scottish Criminal Cases Review Commission (SCCRC).
The SCCRC will decide whether there are grounds to refer the case to the appeal court.
Megrahi was convicted in 2001 of the 1988 bombing of Pan Am flight 103 which killed 270 people.
He is the only person to have been found guilty of Britain's worst act of terrorism.
The Libyan's widow Aisha and his son Ali met recently with Mr Anwar.
It is believed they will present concerns over the evidence which convicted Megrahi, including that given by Maltese shopkeeper Tony Gauci, who died last year.
He was jailed for 27 years but died of prostate cancer aged 60 in 2012 after being released on compassionate grounds in 2009.
Megrahi lost an appeal against his conviction in 2002, with the SCCRC recommending in 2007 that he should be granted a second appeal.
He dropped the second attempt to overturn his conviction in 2009, ahead of his return to Libya. He continued to protest his innocence until his death.
The Pan Am flight exploded at 31,000ft over Lockerbie, in the south of Scotland, on 21 December 1988.
As well as 259 people on board the aircraft, 11 residents of Lockerbie died on the ground as a result of a giant fireball caused when a wing holding thousands of gallons of fuel exploded on impact.
Relatives of some of the victims - led by Dr Jim Swire, whose daughter Flora died on Pan-Am Flight 103 - have already attempted to appeal against the conviction of Megrahi.
The families had argued they should have the right to carry forward the miscarriage of justice appeal for Megrahi.
However, three judges at the appeal court in Edinburgh ruled in July 2015 that this would not be possible under Scots law.
The families' action was not supported by the Victims Of Pan AM Flight 103 group in the United States, which said there was "nothing new" in the appeal.