The air force will not be prosecuted for illegally shipping dangerous chemicals on a passenger plane from Auckland, putting nearly 400 lives at risk.

The Royal New Zealand Air Force was investigated in November 2009 after it breached Air New Zealand's rule not to carry dangerous goods.

The administrative error meant "inadequately prepared and wrongly categorised" chemical oxygen generators were on board a flight from Auckland to Vancouver on August 23, 2009.

The oxygen generators each have a release pin which, if released, can cause the generators to reach temperatures of 260 degrees Celsius and potentially cause an explosion.

In an interim report released today by the director of civil aviation, Graeme Harris, it was revealed the investigation was "not conducted to apportion blame" and the Civil Aviation Authority (CAA) will not prosecute the air force "due to the passage of time".

An inspection report by the CAA's manager safety investigation, Ben Smith, found that "significant failings", including incorrect labelling, categorisation and preparation of the cargo meant the dangerous goods were allowed on board.

A final report and recommendations will be released next year.

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- © Fairfax NZ News