A toxicology test has revealed the pilot of the balloon that crashed in Carterton had cannabis in his system, according to an interim report on the crash.
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.
A Transport Accident Investigation Commission (TAIC) interim report, released today, revealed a toxicology report found Mr Hopping had cannabis in his system.
Lead investigator Ian McClelland said the commission has not yet made any findings linking cannabis use to the accident, "although the test results are concerning to the commission".
The interim 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 including analysis, findings, key lessons and recommendations is due next March.
Mr McClelland said the inquiry drew on ground and balloon-based photography of the flight, a large number of eyewitness accounts, and weather reports.
The TAIC's ongoing investigation was pursuing seven main lines of inquiry, including whether a malfunction contributed to the crash, balloon and pilot performance, and the effects of substances on pilot performance.
It was also looking into the certification and registration of balloons, the maintenance and continuing airworthiness of balloons, the regulatory framework around ballooning in New Zealand, and a review of wire strikes and in-flight fires involving balloons in New Zealand and elsewhere.
Mr McClelland confirmed that commercial hot air ballooning operations had from May been required to meet new certification requirements, with the introduction of new civil aviation rules covering adventure aviation.
The interim report comes after the commission in February made an urgent safety recommendation urging the Civil Aviation Authority to carry out inspections on all 73 balloons in New Zealand.
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.