Chinese Grand Prix latest: Ferrari deny breaking rules. Ferrari have prepared a document to be circulated among the teams that explains what went wrong.

What exactly happened in the pit stop that left a Ferrari mechanic with a broken leg during the Bahrain Grand Prix? Andrew Benson, analysis and opinion from the BBC’s chief Formula 1 writer, explains the incident which took place in the previous race.

Questions have been raised after team boss Maurizio Arrivabene said in a news conference that the problem was with “the electronic device that gives the green light” to the driver to go.

Some rival teams took this to mean that the pit-gantry light was triggered by sensors on the wheel and/or wheel guns. And that would be a contravention of the technical regulations, which say that on the wheel assembly “sensor systems may only act passively”.

But a Ferrari spokesman insisted to BBC Sport that the process was “not fully automatic” and that a sensor failure was not to blame.

Ferrari have prepared a document to be circulated among the teams that explains what went wrong – blaming a series of human errors. It says the following:

– Ferrari’s wheel guns have sensors to measure both the tightness of the nut and the distance it has moved on to the wheel. But in Raikkonen’s stop the mechanic on the left rear wheel missed the nut, but pressed the gun to undo it. He put the gun back on the nut to have another go but reversed the direction to tighten. That meant the system registered the nut as undone, then tightened and in the right place. So the sensor assumed the wheel had been changed when it hadn’t, and gave the all-clear.

– The rear jack man and overall pit stop controller both hold buttons down which they release to turn the pit light to green. Both did this despite the problem on the left rear. The rear jack man didn’t notice the wheel hadn’t been changed and the controller was unsighted and did not see that corner of the car.

– The mechanic who was injured, Francesco Cigorini, was standing with his left leg in front of the wheel, so was caught by the car when Raikkonen accelerated away

Ferrari are to add an extra observer with an over-ride button in an attempt to ensure such a conflation of circumstances cannot happen again.

Governing body the FIA is satisfied with this explanation. F1 director Charlie Whiting has some concerns about the spate of five pit-stop errors in three weekends and recognises these are down to the pressures on mechanics to get stops down to two seconds but is not minded a this stage to take action, such as forcing a minimum pit-stop time. He is happy with the safeguards the teams have in place.

The FIA’s position is that systems should be set up to eliminate the possibility of human error as much as possible but that the final one in releasing the car should be a conscious one by a person.