Senior air force commanders are under investigation over the Anzac Day tragedy which left three staff dead and another seriously injured - but there is only a month left to lay charges.
The detail has emerged in a letter from the air force to the parents of Ben Carson, one of the men killed.
Andrew and Pauline Carson were told by Chief of Air Force Air Vice-Marshal Peter Stockwell a 20-month-long investigation was still going into the 2010 crash north of Wellington.
The letter sent to the Carsons said the next phase of the investigation "which concerns the role of higher commanders is still under review".