The 28-year-old and pilot David Ibbotson died when the single-engine plane they were travelling in crashed into the sea to the west of Alderney while en route from Nantes to Cardiff.
Mr Sala’s remains and the wreckage of the plane were discovered days later. Mr Ibbotson’s body has never been found.
An interim report by the Air Accident Investigations Branch last year revealed how the plane went into a series of dives and climbs and made a number of turns before disappearing from the radar.
Toxicology tests on Mr Sala’s remains later showed he had harmful levels of carbon
monoxide in his system shortly before the crash.
Investigators said it was likely Mr Ibbotson was also exposed to similar levels of the deadly gas, which could have caused ‘damage to his brain, heart and nervous system’.
Crispin Orr, chief inspector of air accidents for the AAIB, said: ‘Today marks the anniversary of the accident… and our thoughts are with the families and friends of Mr Ibbotson and Mr Sala at this time.
‘The Air Accidents Investigation Branch has conducted a thorough investigation looking at a number of elements including operational, technical, organisational and human factors that may have caused, or contributed to, this accident.
‘We have worked closely with many specialist organisations including the
aircraft and engine manufacturers and the National Transportation Safety Board in the USA.’
He added: ‘Our investigation is now at an advanced stage and we intend to publish our final report by the end of March 2020.’
