Kimi Raikkonen's faltering defence of the world championship took another knock today when he crashed his Ferrari during the second practice session for the Belgian Grand Prix at Spa.

Raikkonen, beaten into second place by team-mate Felipe Massa in the opening session, was looking to stamp his authority at a circuit where he has won the last three Formula One races when his car snapped sideways in the rain.

There was hardly any run-off area at the swooping downhill left-hand corner and the Finn was helpless to prevent his Ferrari smashing backwards into a tyre barrier.

The incident ripped off the rear wing and meant Raikkonen, 13 points behind championship leader Lewis Hamilton and without a win since the Spanish Grand Prix in April, was unable to improve on his fifth fastest.

Times were relatively meaningless in the afternoon rain squalls.

Fernando Alonso survived a wild moment over a kerb to top the time sheets in his Renault but he was more than one second slower than Massa had managed in the drier morning session. Hamilton was fourth in the afternoon, beaten by Alonso, Massa and McLaren team-mate Heikki Kovalainen.

The rain caused plenty of drama. with Mark Webber first to go off when the Australian braked too late for the right-handed Les Combes corner. His Red Bull careered over the gravel and hit the barrier hard enough to remove a front wheel.

Giancarlo Fisichella was unlucky when his Force India car ran over oil spilled from the rear of Raikkonen's Ferrari and went out of control, spinning backwards into a barrier.

That brought out the red flag while debris was cleared away. But not long after the resumption Nelson Piquet Jnr, in the second Renault, went off in an exact replica of Raikkonen's crash.

Nico Rosberg made a late charge in his Williams to finish sixth in the afternoon, just ahead of fellow Germans Sebastian Vettel and Adrian Sutil.

Toyota's Jarno Trulli and BMW's Nick Heidfeld completed the top 10, with the latter's team-mate Robert Kubica only 11th. The Pole then hit trouble right at the end of the session when his BMW expired during the practice starts and had to be pushed off the grid.

Honda's appalling form continued with Jenson Button and Rubens Barrichello finishing 17th and 18th.