It will be 30 days before a preliminary report into what caused a Qantas jet to violently lose altitude is delivered, investigators say.

More than 70 people on Qantas flight 72 from Singapore to Perth were injured when the Airbus A330-300, carrying 303 passengers and 10 crew, suddenly dropped altitude on Tuesday.

Up to a dozen people were seriously hurt, including some with spinal injuries, after a sudden drop sent the plane into a nosedive, throwing passengers around the cabin.

The Australian Transport Safety Bureau (ATSB) said preliminary data had been retrieved from the flight data and cockpit voice recorders.

An ATSB spokesman said the full interpretation and analysis of the data would take some time.

A preliminary review of the data indicated the aircraft climbed about 200 feet from a cruising level of 37,000 feet before the aircraft pitched nosedown and descended about 650 feet in about 20 seconds before returning to cruising level.

“This was closely followed by a further nose-down pitch where the aircraft descended about 400 feet in about 16 seconds before returning once again to the cruising level,” the spokesman said in a statement.

Injured passengers would be interviewed to understand what occurred in the cabin and all passengers would be provided with a copy of the ATSB’s preliminary report to be released in 30 days.

A Qantas spokesman said today the company would contact each of the flight’s passengers and deal with those injured on a case by case basis.

“We will be arranging to refund the cost of all the Qantas travel on their itinerary in the form of an ex gratia payment,” he said.

“We will also provide each customer with a Qantas travel voucher for the value of an equivalent flight between Australia and London.”

Qantas would talk directly to passengers who sustained injuries in the incident, the spokesman said.

“We will be talking to our customers directly about any other needs according to their individual circumstances and in particular in association with any injuries sustained as a result of this incident.”

Aviation law firm Carter Capner Law said the incident highlighted an urgent need to update Australia’s international passenger compensation regime.

Lawyer Peter Carter said the federal government failed to ratify a 1999 international treaty that raised passenger compensation limits set 12 years ago.

He said Qantas passenger claims were subject to a maximum $500,000 limit, which would not be enough to compensate seriously injured passengers.

“The international community, apart from Australia, decided long ago the $500,000 liability limit was unfair and inadequate,” Carter said.

The Montreal Convention removed limits on the amount of compensation payable by airlines under certain circumstances.

An ongoing delay to ratify the treaty meant injury and death compensation limits last reviewed in 1996 still applied.

The convention was ratified by 86 other nations, including the United States and New Zealand in 2005.

Investigators say it is too early to blame passenger lap-top computers for causing the jet to abruptly plummet.

Laptops could have interfered with the plane’s on-board computer system, it has been reported.