An audit of the Australian Transport Safety Bureau has found at no stage has it achieved its timeframe targets for complex or short investigations over the past eight years.
The auditor-general report released on Thursday found the ATSB had taken about 19 months to complete complex reports and 5.5 months for short investigation reports.
The agency had aimed to complete 90 per cent of complex probes within 12 months and 90 per cent of short investigations within four months.
"The ATSB has had quality controls and processes in place, however they have not been conducive to the timely completion and review of investigations", the auditor-general found.
The audit recommended the ATSB address the question of timeliness of investigations, report on the use of resources in undertaking investigations, establish more realistic timeframes and seek to benchmark against other similar agencies around the world.
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The agency said in response it was going through a program to improve efficiency, boost its workforce and bring in new technology.
"The ATSB agrees with the recommendations in the ANAO report and has already begun implementing them," it said.
"Greater efficiency and effectiveness will further enable us to fulfil our important function of improving transport safety in an operating environment of continuing change in the aviation, rail and marine industries."
