The tail of the Boeing 747 -- which crashed Thursday at Halifax International Airport -- hit the runway twice during takeoff, and then broke off after hitting a mound, investigators confirmed Friday.

The investigation into the crash, which killed all seven crew members, has just begun. Officials are trying piece together why the MK Airlines cargo plane was barely airborne when the accident occurred.

Bill Fowler, a spokesman for the Transportation Safety Board of Canada, said the tail struck the runway twice -- once about 250 metres from the end of the runway, and again with about 170 metres to go.

"There is an indication that the aircraft was slightly airborne, in other words; the scrape trail disappears just a few hundred feet before the berm." At the antenna-topped mound, the plane broke in two, he said.

With its tail torn off, the rest of the fuselage flew into the bush, cutting a kilometre-long swath before coming to a stop.

This is the fourth crash in 12 years by Britain- and Ghana-based MK Airlines. The other three were in Nigeria -- all during final approach to landing. The most recent, involving a 747 in 2001, killed one crew member.

Fowler said earlier Friday that he's not looking to lay blame at this point.

"What we're looking at is not individual actions specifically, but more, if indeed an error was committed, and we don't know that -- we would want to know why," he said.

"The important part is the 'whys' behind what has occurred."

Pressed by reporters to suggest what could have caused such a crash, Fowler would only say there are a number of scenarios that demand attention.

"From the aircraft loading to the aircraft performance -- whether all the engines were operating -- we're just going to go through, systematically, each of the elements that could produce a scenario such as this and we'll go where the data and analysis leads us."

In an interview with The Canadian Press on Thursday, a pilot familiar with large planes said their tails do occasionally touch tarmac when the pilot pulls the nose off the ground.

Known as 'rotation', it's so common many large planes have protection built-in to the tail, and pilots can typically recover.

"It doesn't happen that often,'' said the pilot, who didn't want his name used. "You can encounter turbulence right at rotation.''

A MK spokesperson told CP the aircraft was in the process of rotating when it crashed.

Victims identified

Headed from Connecticut to Spain with a load of tractors and parts, computer gear and more than 50,000 kilograms of fish, the Boeing 747-200 had just refuelled when it crashed before 4 a.m. local time on Thursday.

The dead are described as nationals of the U.K. and Germany who lived in South Africa and Zimbabwe.

At a media briefing on Friday afternoon, MK Airlines operations manager Capt. John Power said his company had contacted each of the crew's families with the grim news.

"I actually knew each of them personally," Power said, naming the seven crew. "It's actually quite hard to express how I'm feeling right now... but for now my thoughts go to their families."

Vouching for the experience of the crew flying the plane out of Halifax on Thursday, MK Airlines operations manager Capt. John Power said the 747 crews "generally have a high level of experience."

"None of the crew members flying the plane were involved in any of the previous accidents," he said.

"I personally have flown with the senior captain on board that aircraft for 14 years, and as far as the other crew members are concerned, they have all had previous flying experience on DC-8 aircraft."

With investigators from Canada, the United States, the United Kingdom and Ghana in Halifax for the accident probe, former aviation accident investigator Tom Hinton says it takes time to coordinate the effort.

Individual committees will investigate witness accounts, the airliner's electrical system and its data and voice recorders, he says, and then submit reports to be compiled into a final document.

But the investigation won't even begin until the painstaking process of documenting the entire crash site is complete.

"They have to document all of the wreckage in situ before anything is moved," Hinton told CTV's Canada AM on Friday. "Everything is photographed and documented before it's even moved."

The RCMP is treating the crash as a potential criminal investigation for now, following witness reports of explosions during the crash. But investigators said they had no reason to believe an explosion had brought down the plane.

After numerous cancellations and delays,
Halifax International Airport is now back in limited operation. HIAA spokesperson Pat Chapman says airport staff are focused on cleaning up the fuel spilled in the crash.

It will be late November before airport navigation equipment damaged by the out-of-control wreckage can be replaced, she added.

With files from The Canadian Press