INVESTIGATORS probing Michael Schumacher's skiing accident have ruled out faulty skis, inadequate signage and excessive speed as possible causes of his life-threatening off-piste fall in the French Alps.

They said signs marking the edge of the piste Schumacher skied off just before the accident on December 29 were in line with legal requirements and said the German Formula One legend had appeared in control of his speed.

Schumacher, 45, has been in a medically-induced coma since he fell on an off-piste section between two slopes in the ski resort of Meribel and slammed his head on a rock, prompting his evacuation to a hospital in the city of Grenoble.

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Investigators probing the ­accident are seeking to determine why it happened, and whether anyone - the resort, the ski rental shop, Schumacher himself - is at fault.

Patrick Quincy, the prosecutor in charge of the probe, said rules determining how to mark the edges of ski slopes had been "respected" and the racing driver had deliberately skied into the off-piste area.

Stephane Bozon, one of the policemen involved in the probe, said the skis were not the cause of the accident after speculation one of the safety releases on Schumacher's skis did not operate properly.

Mr Quincy added: "Speed is not a particularly important element for us."

The prosecutor said a two-minute-long film taken by a camera on the former racing driver's helmet has been studied to try to discover what caused the accident and it had helped rule out speed as a major factor, although the film is to be re-examined frame-by-frame by experts in the coming days.

Lt-Colonel Benoit Vinnemann, head of the regional gendarmerie investigation team, said Schumacher's speed was "perfectly normal for a competent skier in this kind of terrain".

Mr Quincy said "no elements" had been discovered so far to support reports Schumacher had left the official piste to help another skier in difficulties. He said the seven-times Formula One champion had left a clearly marked "red", or moderate, slope to enter an area of powdery snow dotted with large rocks.

While skiing between three and six yards from the piste, his skis struck a rock hidden in the snow. He was thrown head-long for two to three yards until his head struck one of the rocky outcrops.

The French investigation will decide within the next two or three weeks whether there is any evidence to merit a full criminal inquiry. Mr Quincy said the signs and barriers, warning skiers where the official piste ended, were "perfectly within normal procedures".

He was asked whether the route taken by Schumacher was a "de-facto piste" - an unofficial trail often taken by skiers and tolerated by the managers of the Meribel resort. He said that he could not reply at this stage.

The proscutor said 50 similar investigations into serious skiing injuries were conducted each year by his office, which covers 60% of French Alpine winter resorts. They were all studied, he said, with the same "rigour" as the Schumacher accident.

He was not aware of any ­previous, serious incident at the spot where the former racing champion crashed.

Asked whether he believed there might be a criminal prosecution for negligence, Mr Quincy said: "As the investigation stands, I am not able to reply to that question."