Lewis Hamilton fastest in Spain as Fernando Alonso breaks down
Lewis Hamilton set the pace as Mercedes impressed in first practice at the Spanish Grand Prix.
Hamilton was 0.029 seconds quicker than team-mate Valtteri Bottas, and a second clear of Ferrari's Kimi Raikkonen and Sebastian Vettel in third and fourth.
Red Bull's Max Verstappen was fifth, just 0.250secs behind Raikkonen.
McLaren-Honda's dismal season of unreliability continued, with Fernando Alonso sent into a spin by a major engine failure on his first lap.
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Alonso spun to a halt in a cloud of smoke with oil pouring from underneath the engine after it failed coming out of Turn Two on his first lap. The Spaniard then left the track to go back to his hotel. Honda blamed the failure on "an oil leak" and said Alonso would be back out with a new power-unit in second practice.
Alonso posted a tweet saying: "Keeping the body active," accompanied by an emoji with a halo and a photograph of himself with his trainer playing tennis.
Honda have a small upgrade on the engine for this weekend but said the one he was using had previously run in Australia and China and in Bahrain until qualifying.
In lovely spring sunshine and under a beautiful blue sky north of Barcelona, the teams spent the session evaluating the upgrades they have brought to this race.
All the teams have new aerodynamic parts, as is traditional at this first European race of the season, and the most striking are on the Mercedes.
The silver cars have a narrower nose, under which is fitted a unique new snow-plough style aerodynamic shaping device, as well as new parts all the way along the side of the car.
So far, they appear to be working well, and Hamilton and Bottas traded times throughout the session, rarely separated by more than a few hundredths of a second.
Hamilton arrived in Spain determined to make amends for a poor weekend two weeks ago in Russia, where he finished fourth and Bottas won.
Bottas, by contrast, has made it clear that his focus has shifted to trying to win every race after an up-and-down start to the season in which he has been alternately impressive - with his first win in Russia and first pole in Bahrain - and not, such as when he spun behind the safety car during the Chinese Grand Prix.
The two men are separated by 10 points in the championship, with Hamilton ahead and 13 points behind Vettel.
Ferrari also have a series of aerodynamic changes on their car, as do Red Bull, who are hopeful their upgrade will clos the one-second gap that has separated them from the front-runners so far this season.
It is too early to make any conclusions about relative pace, not least because Vettel's session was disrupted by a gearbox problem on the pit straight.
He managed to pull of into the pit lane exit, from where the car was recovered and the Ferrari mechanics were able to repair the car and send him out again to set his fastest time.