Germanwings co-pilot Andreas Lubitz, who is suspected of deliberately flying a German airliner into the French Alps, may have rehearsed the plane’s fatal dive during an earlier flight on the same day, a new report by French investigators reveals.

The preliminary report into the tragic crash, published on Wednesday by the Bureau of Investigations and Analyses (BEA), showed the co-pilot repeatedly set the Germanwings plane’s altitude to 100 feet during its outbound flight to Barcelona, Spain, from Düsseldorf, Germany, on March 24.

The manoeuvres, which were captured by the plane’s flight data recorder, took place while the flight’s captain had left the cockpit temporarily.

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Information in the 29-page document suggested more evidence that the 27-year-old co-pilot crashed the Airbus A320 intentionally, after locking captain Patrick Sondheimer, 34, out of the cockpit on its return leg to Düsseldorf.

Victorians Carol Friday and son Greig were on board the fatal Germanwings fight.

The flight crashed into the French Alps at a speed of 700km/h, killing all 150 people on board – including Melbourne nurse Carol Friday, 68, and her 29-year-old son Greig.

The report added that on several occasions – again with the captain out of the cockpit – the altitude dial was set to 100ft (30m), the lowest possible reading, despite instructions by air traffic control in Bordeaux to set it to 35,000ft and then 21,000ft.

It was also reset on one occasion to 49,000ft, the maximum altitude.

The changes apparently happened during a five-minute period, the report said.

Earlier investigations into the incident revealed Lubitz’s actions could “only be deliberate”.

Lubitz was left in control of the Airbus A320 after the captain left the cockpit to go to the bathroom, but refused to reopen the door for his colleague.

“One can then hear several calls from the commander asking to be allowed into the cockpit,” Marseille prosecutor Brice Robin said of the cockpit audio recordings.

“He knocked on the door and there was no answer from the co-pilot either.”

Lubitz can allegedly be heard breathing calmly within the cockpit right until the final impact, which means he would have been alive.

He had been on the job since September 2013 and had 630 hours of flying experience.

Investigations by the German police later revealed that Mr Lubitz had a history of severe depression dating back to 2009, and in the days before his final flight, scoured the internet for methods of committing suicide.

Lufthansa is the parent company of Germanwings airline.

A graph in the report shows the selected altitude on the previous flight was reduced several times to 100ft.

Location of Germanwings plane crash.