Fernando Alonso rear wing mystery explained

Ferrari driver Fernando Alonso was involved in a mysterious incident during the Chinese Grand Prix when his drag-reduction system overtaking aid deployed in a forbidden area while he was trying to pass the Mercedes of Michael Schumacher.

The devices - known as DRS for short - have been introduced to Formula 1 this year in an attempt to make overtaking a little easier.

Drivers can use their DRS in one designated zone on the track and only if they are within a second of the car they are trying to overtake. The driver defending his position is not allowed to use his device.

The device is enabled electronically by systems operated by the FIA, the sport's governing body. It works by lifting the upper of the two parts of the rear wing, 'stalling' the wing, reducing drag and therefore increasing straightline speed.

In Shanghai, the DRS zone was on the long back straight. It started 750 metres before the hairpin at the end of the straight and ends as soon as the drivers hit the brakes.

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But at one stage, while Alonso was still behind Schumacher, television viewers saw the Spaniard's wing open between the hairpin and the final corner on lap 23.

BBC Sport has learnt that an error caused Alonso's DRS to 'offset' on that lap.

That meant it was not enabled until 300m before the end of the straight, and was then available after the corner for a short time.

This meant that he gained no advantage from the situation - in fact it actually caused him a disadvantage - so was given no penalty.

FIA officials are still investigating what caused the error.

Alonso eventually passed Schumacher two laps later, on lap 25, by getting a better exit out of the hairpin.

He finished the race in seventh place. It was won by McLaren's Lewis Hamilton from Red Bull drivers Sebastian Vettel and Mark Webber.

Alonso also had problems with his DRS in the previous race in Malaysia a week ago. Then, it stopped working and he was unable to use it for much of the race.