Cannabis found in the system of the Carterton balloon crash pilot is a "significant safety concern'' but it is too early to say whether it caused the tragedy, the lead crash investigator says.
Pilot Lance Hopping, 53, and 10 passengers died when the hot air balloon collided with power lines and caught fire near Carterton on January 7. There were no survivors.
An interim Transport Accident Investigation Commission (TAIC) report, released today, revealed a toxicology test had found cannabis in Mr Hopping's system.
The report outlines the facts so far and sets out continuing lines of inquiry, but does not provide an analysis of what happened. A full report is due by next March.
Lead investigator Ian McClelland said cannabis use had not been identified as a cause of the accident but was "obviously a significant safety concern''.
The revelation comes the day after a TAIC report into a fatal plane crash at Fox Glacier in 2010 found two commercial skydivers on board had cannabis in their systems.
That prompted a safety recommendation to the Transport Ministry, urging the introduction of a drug and alcohol detection and deterrence regime for people employed in safety-critical transport roles.
At present, there is no legal requirement for random drug testing of the likes of commercial balloon pilots or skydivers.
Mr McClelland said it would be up to the ministry and the Civil Aviation Authority (CAA) to determine how a drug testing regime should be implemented.
He would not reveal the level of THC, a cannabis constituent, found in Mr Hopping's system.
Levels varied widely between individual cannabis users and factors included frequency of use, potency and smoking methods.
"There are simply too many variables to state a figure without giving the background information, and further research needs to be done to confirm both the figure and put it in context,'' he said.
"We need to have the results analysed again independently. We need to put it in context in terms of how long the autopsy took, the results took, and also the background of the pilot himself.''
The results of alcohol testing on the pilot were inconclusive.
Mr McClelland would not say how the families of the victims reacted to news of the positive drug test, saying the TAIC had met with them in private and it was inappropriate to comment.
CAA chief executive and director Graeme Harris said he was "very disappointed'' by evidence of drug use in recent TAIC reports.
"The CAA is planning an education and safety promotion campaign on this issue, consistent with the advice provided to the commission by the Ministry of Transport in its report into the Fox Glacier accident released yesterday.''
Responding to that advice, Transport Ministry aviation and maritime general manager Bruce Johnson said changing individuals' illegal drug use was challenging.
The ministry would encourage the CAA to step up its education efforts, but in the past it had been unconvinced that the benefits of compulsory random drug and alcohol testing outweighed the cost.
"Specific rule changes may not always be the best interventions to achieve desired safety outcomes. Non-regulatory interventions can often be more appropriate.''
The ministry would monitor international testing regimes, including recent aviation rule changes in Australia.
The families of the victims, who have been briefed on the interim report, have asked for privacy from the media.
The Masterton locals killed in the crash were Mr Hopping, Valerie Bennett, 70, and husband and wife Desmond and Ann Dean, aged 70 and 65.
The victims from the Wellington region were Ms Bennett's cousin Denise Dellabarca, 58; husband and wife Howard and Diana Cox, aged 71 and 63; Lower Hutt couple Stephen Hopkirk, 50, and Belinda Harter, 49; and young Wellington couple Chrisjan Jordann, 21, and Alexis Still, 19.
