An in-flight battery fire was the likely cause of a glider crash that killed a 72-year-old pilot in Kaikohe in 2017.
It was the first battery fire on a glider in New Zealand.
The Civil Aviation Authority released its safety investigation report into the crash today.
It said "fumes and smoke" would have filled the cockpit and caused pilot Ricco Legler, of Russell, to lose control of the glider.
The crash was "not survivable".
The battery was a part of an Electro 40/30 electric motor used for self-launch take-offs and to sustain flights.
Aviation Safety deputy chief executive Dean Winter said flyers should ensure batteries are charged and properly maintained according to the manufacturer's instructions.
"Battery fires burn at a very fast rate releasing significant energy and toxic fumes. Within seconds a cockpit can be filled with toxic smoke.
"These fires can be deadly and spread quickly."
Legler, an experienced pilot, launched his glider from Kaikohe aerodrome at 1.40pm on November 16, 2017.
Sometime between 2.15pm and 5.30pm, the fire broke out while the glider was soaring.
The glider was making an emergency descent and approach to Kaikohe aerodrome when it exceeded its speed limitations.
This led to structural failure of the wings and the glider broke up in-flight, the report says.
Legler, who was a member of the local gliding club, held a glider pilot certificate and private pilot helicopter licence.
He had 592 hours experience on gliders, with 87.9 hours on the glider ZK-GEL.
At the time of the crash, there were no other battery-powered gliders in the country, Winter said.
"We are also concerned any lithium polymer battery in any device or aircraft can cause a fire."
The authority also recommended pilots consider fire detection, containment and fire proofing systems; manufacturers address in-flight battery fires and outline how to check and charge batteries properly in flight and maintenance manuals.