Nico Rosberg topped the opening practice session for the Chinese Grand Prix, which was stopped twice following a series of tyre problems that left debris on track.
Felipe Massa suffered two left-rear tyre deflations before Kevin Magnussen experienced a left-rear blowout on the long back straight at high speed. Early investigations suggest a technical problem on Massa's car, most likely something rubbing against the tyre, caused his issues. The first occurred 20 minutes into the session in the long right-hander at Turn 1 before the tyre let go in Turn 3 and the second following the long right-hander in Turn 13 20 minutes later.
Massa managed to recover back to the pits both times, but left debris on the track that appeared to cause Magnussen's puncture later on. Investigations by Pirelli and the teams involved are continuing ahead of FP2, but the rest of the drivers went back out with eight minutes remaining to clock up more laps.
Investigations with @pirellisport show no sign of a puncture so the team will investigate the cause of the blow out https://t.co/Y9iWGfGX4I
— WILLIAMS RACING (@WilliamsRacing) April 15, 2016
Rosberg set his fastest time in the flurry of action at the end, using the soft tyres to move ahead of team-mate Lewis Hamilton by 0.146s. His session ended a lap or two early when his engine kicked into limp home mode. The team informed him that it looked like an engine issue while gear shifts remained okay, which may lead to an engine change later in the weekend but should see him avoid the same five-place grid penalty hanging over Hamilton ahead of Sunday's race. Both drivers struggled for grip throughout, resulting in Hamilton spinning twice at Turn 11 when he lost the rear of the car.
Ferrari finished the session in third place, with Sebastian Vettel 0.628s off Rosberg. Daniel Ricciardo split the two Ferraris, just under 0.4s off Vettel and just under a tenth faster than Raikkonen, who spent more time running the medium tyre than his team-mate Vettel, who focused on the softs. Daniil Kvyat was sixth fastest ahead of Carlos Sainz's Toro Rosso, Jenson Button's McLaren -- the only driver in the top ten to use the super-softs --, Nico Hulkenberg's Force India and the second Toro Rosso of Max Verstappen.
On his first session back in the car since the Australian Grand Prix, Fernando Alonso was 12th fastest after 11 laps in the in the McLaren. He will go for further medical tests on his fractured ribs before FP2 to ensure he can take part in the rest of the weekend.
Along with Magnussen and Massa, Esteban Gutierrez was the only driver not to set a time after experiencing an electrical issue on his Haas after two laps.