There have been many attempted explanations for the cause of his death, but no consensus has been reached. His death was a turning point in the safety of Formula One, as many safety measures have since been implemented. The Grand Prix Drivers' Association was reformed later in 1994, and the association has contributed to these changes.

BACKGROUND

   
On May 1, 1994, Senna took part in his third race for the Williams team, the San Marino Grand Prix at the Imola circuit. Although he would not finish it, Senna started his final Formula One race from pole position.

That weekend, he was particularly upset by two events. On Friday, during the afternoon qualifying session, Senna's protégé, F1 newcomer Rubens Barrichello, was involved in a serious accident that prevented him from competing in the race. On Saturday, the death of Austrian driver Roland Ratzenberger in qualifying, deeply upset Senna, reinforcing his safety concerns and made him consider retiring from the sport. Ironically, he spent his final morning meeting fellow drivers, determined after Ratzenberger's accident to take on a new responsibility to re-create the Grand Prix Drivers' Association, a Drivers' Safety group to increase safety in Formula One. As the most senior driver, he was offered to take the role of leader in this effort.

 The Accident

On Sunday, Pedro Lamy and JJ Lehto were involved in a starting-line accident. Track officials deployed the safety car to slow down the field and allow the debris from the starting accident to be removed. The cars proceeded under the safety car for 5 laps.

On lap 7, from the onboard camera of Michael Schumacher's Benetton, Senna's car was seen to break traction twice at the rear, go off the track at Tamburello corner and strike an unprotected concrete barrier. Telemetry shows he left the track at 310 km/h (190 mph) and was able to slow the car down to 218 km/h (135 mph) in slightly under 2 seconds before hitting the wall.
A map of the circuit per 1994 layout, with the Tamburello corner encircled.

After Senna's car came to a halt, he remained motionless in the cockpit. Although the car had suffered a high speed impact with the wall, the accident did not have the typical hallmark of an especially devastating racing crash. The car simply seemed to understeer strongly off the track, hit the wall at a shallow angle, tearing off the right front wheel and nosecone, lift slightly with the nose as it straightened, and spin mildly to a halt.

Although the crash seemed benign, it was immediately evident that Senna had suffered some form of injury because of the manner in which his helmet was seen to be motionless and leaning slightly to the side. In the seconds that followed his head was seen to move to one side slightly causing false hopes to be raised. A considerable amount of time passed before medical units came to his aid, with fire marshals having arrived at the car and unable to touch Senna before qualified medical personnel arrived. Television coverage from an overhead helicopter was seen around the world, as rescue workers gave medical attention. Close inspection of the area in which the medical staff treated Senna revealed a considerable amount of blood on the ground. The race was stopped 1 min. 9 seconds after Senna's crash.

Approximately 10 minutes after Senna's crash, a miscommunication in the pits caused a Larrousse car piloted by Érik Comas to leave the pit lane and attempt to rejoin the now red flagged Grand Prix. That incident with Comas was spotted by Eurosport Commentator John Watson as the "most ridiculous incident I ever saw at any time in my life". Frantic waving by the marshals at Senna's crash site prevented the Larrousse from risking a collision with the medical helicopter that had landed on the track.

Professor Sidney Watkins, a world-renowned neurosurgeon and Formula One Safety Delegate and Medical Delegate, head of the Formula One on-track medical team, who performed an on-site tracheotomy on Ayrton Senna, reported:

    He looked serene. I raised his eyelids and it was clear from his pupils that he had a massive brain injury. We lifted him from the cockpit and laid him on the ground. As we did, he sighed and, although I am totally agnostic, I felt his soul depart at that moment.

Accident analysis


In 2004, a television documentary by National Geographic called Seismic Seconds: The Death of Ayrton Senna was screened worldwide. The program considered the available data from Senna's car to reconstruct the sequence of events that led to the fatal crash. The program concluded that an unusually long safety car period had reduced the pressures in Senna's tyres, thereby lowering the car. As the car entered the Tamburello bend, the skid-plate on the bottom of the car connected with the ground, rendering the car's steering and lateral grip useless. Senna reacted with lightning-fast reflexes, but as the car passed over the bump and regained grip the steering wheel now was in a right-lock corrective position, the car effectively drove off the circuit.

To many within the F1 world including some drivers of that era who had raced at Imola, the conclusions drawn from low tyre pressure as a cause of the accident seem implausible. Telemetry recorded that Senna took the bend at 306 km/h (190 mph) on lap 6 with cold tyres. The information released in the trial stated that Senna started the race with 86 litres of fuel and had planned a two stop race strategy, one fewer than Schumacher, who started the race lighter on a 3 stop strategy. The theory that low tyre pressure caused the crash was defeated in court when Stefano Stefanini, head of Bologna's traffic accident unit, testified that Senna, with a heavier car than Michael Schumacher and Damon Hill, recorded a time of 1.24.887 on the sixth lap, Senna's only lap at race speed and the 3rd fastest lap of the race. Michele Alboreto and other drivers of the era claimed that given Senna's lap time, his tyres would have been at race temperature by the 7th lap and could not have been a factor in the crash.

Some drivers indicated that Senna's crash was due to driver error. Michael Schumacher, who had followed closely behind the Brazilian before the crash, gave the following account at the subsequent winners' press conference:

    I saw that his car was already touching quite a lot at the back on the lap before, the car was very nervous in this corner, and he nearly lost it. On the next lap he did lose it. The car touched with the rear skids, went a bit sideways, and he just lost it.[4]

Damon Hill, Senna's teammate at the time of his death, had this to say in an interview given on the subject 10 years later:

    I am convinced that he made a mistake, but many people will never believe that he could. Why not? He made many mistakes in his career. I have listened to and read endless theories about why, or how, he could have crashed on such a 'simple' corner like Tamburello. No-one other than Ayrton Senna and me know what it was like to drive that car, through that corner, in that race, on that day, on cold tyres. He was identified with pushing to the limit and beyond. It was not the fault of anyone else that he kept his foot flat when he could have lifted.[5]

The ban on active suspension affected Williams more than any other team as it was the key development that had helped make the Williams car the class of the field during 1992 and 1993 seasons. After active suspension was banned in 1994 the Williams drivers complained of severe handling problems and a twitchy rear-end. The FW16's new rear end was introduced at Imola. It was ironic that at the beginning of 1994 Senna himself told the press that he would be surprised if there would be no large accidents that year. He referred to the fact that after the wide "white label" 18 inch wide Goodyear slicks were replaced for 1993 by the narrower "yellow label" 15 inch wide slick, now the technology at the very core of the cars, the science around which they had been based for the last few years (active suspension, traction control and ABS) was also banned for 1994. He surmised that the cars would have trouble staying on the road, which is exactly what was observed at the beginning of 1994. J. J. Lehto damaged his vertebrae at Silverstone in January (as did Jean Alesi, causing him to miss Imola) prior to Ratzenberger's and Senna's fatal accidents at Imola. During qualifying for the next race at Monaco, Karl Wendlinger suffered an accident which left him in an induced coma; Ratzenberger's replacement, Andrea Montermini, broke his feet in the Simtek in Barcelona and Eddie Irvine was banned for three races after causing an accident during the season-opening Brazilian Grand Prix. None of these accidents were deemed to be caused by driver error (except Irvine's), although there is no evidence to suggest that the accidents were caused by the ban on driver aids.

There are other factors – Senna did not like the position of the steering column relative to his seating position and had repeatedly asked for it to be changed. At Imola Senna found himself in a car with his team's engineers struggling to cope and adapt to the ban of active suspension. Patrick Head and Adrian Newey agreed to Senna's request to lengthen the FW16's steering column, but there was no time to manufacture a longer steering shaft. The existing shaft was instead cut, extended by inserting a smaller diameter piece of tubing and welded together with reinforcing plates. Many surmise, based on comparing hours of onboard video footage from Brazil and Imola that the movement of the steering wheel during the race at Imola was completely abnormal. Senna on his final lap is seen turning the wheel left to full lock with no movement of the front wheels. Others have raised suspicion at what can clearly be seen on the onboard footage as Senna looking down at his steering wheel seconds before entering Tamburello.
Senna's distinctive helmet

The irony of the on board video available from Senna's car is that the final seconds of footage are missing. The approximately 1.5 seconds of remaining video which would have provided a definite answer as to the cause of Senna's death were lost in an act of astounding coincidence when the TV race director decided to switch camera signals at the very instant the Williams started to leave the track.

Perhaps unsurprisingly, numerous rumours abound that the remaining 1.5 seconds are not lost and reportedly show Senna's steering wheel clearly coming off in his hands as his car is leaving the track. In addition to this, the video shown in the Court Room on May 14, 1997 stopped 0.9 seconds before the impact [6], causing numerous questions. Although allegations exist that this video has been seen by a number of people at the top level of motorsport, there is no evidence to support its existence.

The Williams team was entangled for many years in a court case with the Italian prosecutors over manslaughter charges, but they were found not guilty and no action was taken against Williams. In 2004, the case was re-opened, but closed again in 2005 when there was no new evidence.

During the trials , Fabrizio Nosco, a Regional technical commissioner, testified that both of the vehicle's black boxes were intact, except for minor scratches. He said "I have seen thousands of these devices and removed them for checks. The two boxes were intact, even though they had some scratches. The Williams device looked to have survived the crash.". In a move that disrespected FIA regulations at the time, Charles Whiting, a FIA official, handed the black boxes to Williams before the regulating body's own investigation into the accident. Williams claimed the black boxes were unreadable, and the boxes returned for the court proceedings were indeed unreadable, a full month after the accident. The black boxes would have put to rest the cause of the accident.

At the conclusion of the Italian trial, Senna's FW16, chassis number 02, was returned to the Williams team. The team reported that the car was in an advanced state of deterioration and was subsequently destroyed. The car's engine was returned to Renault, and its fate is unknown.

His death was considered by many of his Brazilian fans to be a national tragedy, and the Brazilian government declared three days of national mourning. More than 1 million persons followed Senna's burial in São Paulo. Senna is buried at the Cemitério do Morumbi in his hometown of São Paulo.

Legacy

Following the deaths of Senna and Ratzenberger, many safety improvements were made. Although other drivers had died before him, Senna had arguably the highest profile. Improved crash barriers, redesigned tracks and tyre barriers, higher crash safety standards, and higher sills on the driver cockpit are among the measures that were subsequently introduced. Since Senna's death, no drivers have died behind the wheel of a Formula One car, despite large accidents still occurring.

After the crash, race officials found a furled Austrian flag in the cockpit of Senna's car. It seems that Senna had intended to dedicate his 42nd victory to the memory of Roland Ratzenberger.