Mr Dumbrell, a former Tumut deputy mayor and passionate aviator, was found dead inside the wreckage of his amateur-built Rand Robinson KR-2 plane near Adelong on October 7.
An update from the Australian Transport Safety Bureau (ATSB) said completion of its draft report had been delayed.
It is expected to be released to directly involved parties for comment this month.
"Feedback from those parties on the factual accuracy of the draft report will be considered for inclusion in the final report," the ATSB investigation report said.
The final report is due to be made available to the public in July.
The 65-year-old's family had reported him missing after he hadn't been heard from since leaving home for a flight to Holbrook two days earlier.
The crashed plane was found about 400 metres from the private landing strip where it took off.
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Ben Dumbrell: his body was found in the wreckage of a Rand Robinson KR-2 plane.
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Collision with terrain involving Rand Robinson KR-2, VH-CTE, near Tumut, NSW on 5 October 2013
Investigation number: AO-2013-174
Investigation status: Active
Updated: 10 April 2014
Completion of the draft investigation report has been delayed and is now anticipated for release to directly involved parties for comment in May 2014. Feedback from those parties on the factual accuracy of the draft report will be considered for inclusion in the final report, which is anticipated to be released to the public in July 2014.
At about 0900 Eastern Standard Time on Saturday 5 October 2013, the pilot of an amateur-built Rand Robinson KR-2, two-seat aeroplane, registered VH-CTE and operated in the ‘Experimental’ category, took off from an airstrip on private property 14 km west of Tumut Airport, New South Wales (NSW). The pilot was reported to have intended to fly the 48 NM (89 km) to Holbrook, NSW, for the weekend.
On the evening of Sunday 6 October, when the pilot had not returned home, he was reported missing and a search commenced. Due to darkness, the search was suspended and recommenced the following morning. During the early morning of 7 October 2013 the aircraft wreckage was found about 400m north-east of the airstrip.
The pilot was fatally injured and the aircraft destroyed.
