Lando Norris' botched pitstop in Sunday's Mexican Grand Prix was caused by a cross-threaded wheelnut revealed McLaren F1 boss Andreas Seidl.
Norris was inside the points and ready to swap his soft tyres for a set of mediums when he headed to the pits on lap 15. The rookie was promptly sent off but suddenly pulled off at the end of the pitlane.
It later transpired that the McLaren crew had doubts about whether the front left wheel had been bolted on correctly or not, and thus told forced Norris to stop, his crew then pulling the car back to its box to control the fitting of the suspected loose wheel.
"We had an issue with the wheelnut going on on one corner, which was cross-threaded, and that was the issue," explained Seidl to Autosport.
"We improved compared to Monza in terms of reaction, we managed to stop the car inside the pit lane and pull it back but obviously it is better to not get to this scenario.
"These pit stops are happening within 2.5 seconds and you try to go to the limit but these happen so quickly, especially when you have the issue of cross-threading, it is bad luck.
"But still we need to learn from it and see what we can do on the technical side and the operation side."
A team that fails to properly execute a pitstop and sends its car off is at risk of being punished for an unsafe release.
The stewards predictably investigated McLaren after its botched pitstop but admitted that they could not determine whether the release had been unsafe or not.
"The team representative stated that the front left mechanic was not sure if the tyre was secured properly therefore they decided to stop the car for caution," stated the stewards in their ruling.
"After reviewing video evidences, the FIA technical delegate could not establish if the car was in an unsafe condition after being released from the pit stop.
"The Stewards considered that with the available evidence it is not possible to determine if the car was released in an unsafe condition."
While Norris was running a lap down on his rivals, McLaren noticed that several parameters on his car were "over the limit". At which point, the Woking-based outfit decided to retire the young Briton.
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