FACTBOX- Imola 1994, Formula One's tragic weekend

(Reuters) - Formula One is remembering Brazilian Ayrton Senna and Austrian Roland Ratzenberger on the 20th anniversary of their deaths in 1994 at the San Marino Grand Prix at Italy's Imola circuit. The following is a brief timeline of that weekend. - - - - * The race was the third round of the year. Triple champion Senna had started on pole position in Brazil and in Japan but had yet to score any points while Benetton's young German Michael Schumacher, in his third full season, had won the first two races. * April 29. In qualifying practice for the race, young Brazilian Rubens Barrichello - in his second season with Jordan - hit a kerb and the car took off at the Variante Bassa, hitting the top of the tire barrier before coming to rest upside down. Barrichello was knocked unconscious and taken to hospital. He suffered a broken nose and was ruled out of the race. "By the time the helicopter took off to take Rubens to hospital we were all fairly confident that he was going to be all right. Spirits were high, congratulations to the medical team were welcomed. The system had worked and the result was joyful." - The late F1 medical delegate Sid Watkins, a close friend of Senna's, wrote in his 1996 book 'Life at the Limit'. * April 30. Final qualifying on the Saturday before the race. Austrian rookie Ratzenberger lost control of his Simtek and hit a concrete wall head-on at the Villeneuve kink. He had damaged his front wing on a kerb on the previous lap, which then apparently failed at around 300kph. Senna, who had been to the scene of accident, turned up at the medical center and was devastated. It was the first driver fatality in F1 in nearly 12 years. "Ayrton was beside himself: He had not been close to death at a circuit before...So many accidents in the past 12 years, so many serious injuries, but nobody irrevocably lost...Ayrton broke down and cried on my shoulder." - Watkins. * Watkins relates how he said to Senna after Ratzenberger's death: "Ayrton, why don't you withdraw from racing tomorrow? I don't think you should do it. In fact, why don't you give it up altogether? What else do you need to do?...give it up and let's go fishing." The Brazilian replied: "There are certain things over which we have no control. I cannot quit. I have to go on." * May 1. Before the race, he had made peace with old, and by then retired, rival Alain Prost. "I miss you," Senna told him. The Brazilian then lined up on pole for the third race in a row, with Schumacher alongside. Finnish driver JJ Lehto stalled his Benetton on the grid. Those behind him managed to avoid the car but Portugal's Pedro Lamy, unsighted, ploughed into the back of it. Neither driver was hurt but nine people were injured by debris. * The safety car, reintroduced into F1 the previous year, came out for five laps which reduced tire temperatures and the race then resumed with Senna leading. On the second lap after the re-start, Senna's Williams speared off at Tamburello and hit a concrete wall. The race was stopped immediately and cars returned to the pit lane. Senna was extracted from the car and flown to hospital. Thirty seven minutes after the crash, the race re-started and was won by Schumacher. No champagne was sprayed. At 6.40 pm Italian time, nearly two and a half hours later, it was announced that Senna had died. * Austrian Niki Lauda summed up the grim weekend: "God has had his hand over Formula One for a long time. This weekend, he took it away." (Reporting by Alan Baldwin, editing by Ed Osmond)