The pilot in January's balloon tragedy in Carterton was flying with cannabis in his system when the crash occurred, killing all 11 people on board, including former Southland Chrisjan Jordann.
Toxicology tests performed on the body of Lance Hopping, 53, four days after the crash, returned positive for cannabis, with the discovery described as "concerning" by investigators.
The findings were part of an interim report issued by the Transport Accident Investigation Commission (TAIC) this morning, four months after the balloon struck powerlines, caught fire and crashed into a field on January 7.
Investigator in charge Ian McClelland was unable to say what amount of the drug had been detected.
The initial results needed to be analysed independently and considered along with the time before the autopsy, and Hopping's background.
"There are simply too many variables to give a figure and further research needs to be undertaken to get a figure and put it in context."
Tests for alcohol had been inconclusive and further analysis was needed, McClelland said.
The report also included a detailed description of the events leading up to the balloon striking powerlines, and the horrific moments shortly after as the basket caught fire.
It describes how Hopping knew the balloon was heading for powerlines, yelling "duck down" to passengers before impact.
The balloon had been travelling parallel to the powerlines for up to seven minutes before the crash.
Passengers then tried to push away from the powerlines after the balloon snagged under a wire, with the balloon ascending at the time of impact.
"As the balloon was trying to rise, it also began to slide along the powerlines towards Somerset Road," the report notes.
"About 15 to 30 seconds after contacting the wires, an electrical arcing occurred.
"A fire erupted shortly afterwards low down on the basket.
"Two of the passengers jumped from the burning basket and shortly after that the power line lying across the top of the basket broke and the balloon then ascended rapidly."
The balloon reached about 150m in the air before the envelope collapsed and the balloon crashed into a field.
Just yesterday TAIC called for an alcohol and drug testing regime to be implemented for people performing activities critical to flight safety, after announcing that two tandem skydive masters had smoked cannabis before a Skydive New Zealand plane crashed after takeoff from Fox Glacier in September 2010.
While this morning's report contains a number of details about what happened on the day, it includes no analysis of those facts, nor any recommendations or key lessons to be learned from the crash.
Instead those findings would be reserved for TAIC's final report due in March next year.
The families of the victims were briefed on the report last month, and it is understood several people have had drafts of the report for weeks, including the balloon company owners, members of Hopping's ground crew, and his fiancee Nina Kelynack.
Further lines of enquiry included whether any malfunction contributed to the crash, balloon and pilot performance, the regulatory framework for balloonists, and a review of other wire strikes around the world.
In February, preliminary findings released by TAIC showed the balloon should not have been in the air on January 7.
The burners and LPG fuel system had not been correctly inspected, the balloon material had not been properly strength-tested, and a safety logbook was left incomplete.
These oversights meant the balloon may have been in breach of Civil Aviation Authority standards, and therefore not "airworthy".
The commission then recommended that the CAA make urgent checks on the maintenance of all 74 balloons in the country - a move labelled labelled as unnecessary and "knee-jerk" by balloon operators.
Later the CAA confirmed that just one maintenance provider was being examined - known to be Hawke's Bay Aviation - and only 16 balloons were potentially not airworthy.
In March, hundreds of people gathered at a civic service in Carterton, including many family members of the victims.
A week later tearful relatives released white balloons in the shape of doves in an emotional dawn memorial service for the victims, which doubled as the start of the Balloons Over Wairarapa festival.
Those killed in the crash were pilot Lance Hopping, 53, of Masterton; Alexis Still, 19, and Cjrisjan Jordann, 21, of Wellington; Lower Hutt couple Belinda Harter, 49, and Stephen Hopkirk, 50; Denise Dellabarca, 58, of Kapiti, and her cousin Valerie Bennett, 70, of Masterton; Masterton couple Ann Dean, 65, and Desmond Dean, 70; and Wellington couple Diana Cox, 63, and Howard Cox, 71.
Subscribe to a digital replica of The Southland Times.
Southland Times subscriber news and information.
Click here for information about advertising with The Southland Times.