The average time taken to complete an FAI has risen by more than eight months In the last year alone.
Four people were killed when Super Puma crashed into the North Sea as it approached Shetland in 2013.
An FAI has been told it would not be realistic to expect the same levels of safety from offshore helicopters as jet aircraft.
Willie Rennie repeats calls for FAI reform on anniversary of crash involving John Yuill and Lamara Bell.
The inquiry has already been delayed once and will now be rescheduled due to coronavirus.
Sophie Parkinson's mother said the decision, which is due to the coronavirus outbreak, is 'depressing'.