A visor tear-off from a helmet caused Fernando Alonso's brake failure during the Spanish Grand Prix on Sunday.
The Spanish driver retired from his home race on lap 26 after complaining of brake problems on the previous lap.
McLaren asked Alonso to pit, and the Spaniard even had problems stopping his car in the pits once he came in.
He locked up the fronts as he came to a stop and the front jack man had to jump out of the way to avoid being hit.
The team has found that the brakes overheated and failed due to a visor tear-off blocking the right rear brake duct and cutting off the air that cools it.
It is understood that the tear off was found in the floor of the car after he stopped, but the team's own pit video revealed it had been blocking the brake duct when the car was moving.
"The brake problem that ended Fernando's race was caused by a stray visor tear-off strip that had become lodged in, and was thereby obstructing cooling air-flow through, a rear brake duct," a McLaren spokesperson told Motorsport.com.