FIA race director Michael Masi was at a loss to explain exactly how a manhole cover had come loose at the Baku City Circuit, causing a serious incident with the Williams of George Russell during first free practice for the Azerbaijan Grand Prix.
The drain cover had been loosened by Charles Leclerc running over it, with Russell then helpless to avoid a big incident when he passed it soon after.
FP1 was swiftly cancelled as the 300+ other drain covers on the circuit required checking, although FP2 was able to start on-time, after F2 qualifying had been pushed back by 30 minutes.
"From our preliminary investigations, it looks as though one of the clamps underneath one of the manholes failed," Masi told Sky Sports. "There is no explanation at this point as to why.
"From a precautionary point of view, there is in excess of 300 manhole covers around this circuit, we have checked every single one. From an FIA perspective, safety is paramount so we cancelled the end of FP1 and we moved F2 qualifying back.
"We told the circuit to take as long as they needed to make sure the job was done properly.
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"From what we've seen so far we're quite confident and we will go through a further programme tonight and a programme for the rest of the weekend.
"In the short time [after F2 qualifying] they have done a few further checks to make sure and everything appears to be in order.
"We've seen these types of incidents happen previously and it's not something that any of us wish upon, but it's no difference to a car when something breaks and you don't know. It happens."