The pilot of an ill-fated Garuda flight which crashed in Indonesia killing 21 people, including five Australians, was singing as he began his descent, a report says.

Indonesia's National Transportation Safety Committee (NTSC) has made a series of recommendations following its investigation of the March 7 crash.

But, despite finding flaws with the pilot's actions - including that he ignored 15 "very loud" alarms to continue with his unstabilised landing approach at excessively high speed and steep descent - it did not recommend any criminal action.

The plane overran the runway in Yogyakarta, central Java, crossed a road, and hit an embankment before exploding into flames in a rice paddy field, 252m from the runway.

The report revealed details of the final minutes of the flight, obtained through analysis of the plane's black boxes.

It found the pilot was "singing" during the approach, below 10,000 feet and prior to reaching 4,000 feet, which was "not in accordance with the Garuda Basic Operations Manual policy for a sterile cockpit below 10,000 feet".

"The pilot was probably emotionally aroused because his conscious awareness moved from the relaxed mode "singing" to the heightened stressfulness of the desire to reach the runway by making an excessively steep and fast, unstabilised approach," the report said.

It found the pilot, who was uninjured, later "fixated" on landing the aircraft, ignoring the 15 loud alarms in the cockpit and two calls from his copilot to abort the landing.

However, there were clues that he realised things were amiss prior to the crash, commenting "Oh, there is something not right", the report said.

"The pilot in command's intention to continue to land the aircraft, from an excessively high and fast approach, was a sign that his attention was channelised during a stressful time," the report said.

The report found the copilot also failed to follow company procedures that required him to take control of the aircraft when he saw the pilot repeatedly ignore the warnings.

Gaurda records showed no evidence that the company provided simulator training for flight crews covering required responses to the warning sirens.

It found the Directorate General of Civil Aviation's surveillance of Garuda had failed to identify safety deficiencies and that authorities had only checked the plane's safety and airworthiness twice in almost a decade.

The airport did not meet international runway standards, and its rescue and firefighting vehicles were ill-equipped and unable to reach the crash site, which may have "significantly reduced survivability".

More than 100 others survived but many suffered horrific burns, including Sydney Morning Herald journalist Cynthia Banham, who has since had one leg amputated and the other partially amputated.

The fire was extinguished more than two hours after the crash.