THE Clutha Fatal Accident Inquiry is sitting for day four of the investigation into the circumstances around the fatal helicopter crash.

This morning the hearing heard from Peter Wivell, a senior inspector of air accidents with the Air Accident Investigation Branch (AAIB).

He is the third expert from the AAIB to give evidence and was today questioned by Procurator Fiscal Depute Sean Smith, who is leading evidence for the Crown.

Mr Smith took the expert through sections of an AAIB report into the final flight of helicopter GSPAO.

Mr Smith's questioning was followed up by Donald Findlay QC, who is acting for the family of Robert Jenkins, one of 10 people who died when the Police Scotland helicopter crashed into the Clutha Vaults on the night of November 29, 2013.

Mr Wivell told the court the helicopter had not been fitted with any kind of recording equipment, which means there are things about the final flight that investigators will never know.

On being asked about the decisions the pilot would have taken with regards switches in the cockpit, Mr Wivell told the court: "The problem with this investigation was a lack of evidence that would have allowed us to answer off definitively questions we could answer off, which is frustrating for everyone and not great with an investigation into safety.

"If we had had an image of the display panels we would be in a much better position to understand events.

"There would have been many things there was a potential to answer off."

Seven safety recommendations were made in a report from the air accident investigations branch following the Clutha crash in November 2013, including the introduction of a flight recorder system that would capture images from the cockpit, audio and information about the helicopter's "pitch and roll".

Mr Findlay said: "I'm interested in what happened in the cockpit in the final moments of the flight."

Mr Wivell replied: "That would be good to know."

Mr Findlay added: "Indeed it would. For a great many people."

When the inquiry sits again at 2pm today further evidence from Mr Wivell will be lead.

Pilot David Traill, 51; PC Tony Collins, 43; and PC Kirsty Nelis, 36, lost their lives in the crash along with seven customers who were in the bar on Stockwell Street.

Gary Arthur, 48; Joe Cusker, 59; Colin Gibson, 33; Robert Jenkins, 61; John McGarrigle, 58; Samuel McGhee, 56; and Mark O'Prey, 44 were all killed while a further 31 people were injured.