“I write these words in steel, because nothing that isn’t written in metal can be trusted.” It took Brandon Sanderson, the American fantasy author, to give due credit to those who analyzed Ayrton Senna’s steering column. The entire criminal trial focused on a central theme: the accident on lap 7 of the San Marino GP was primarily caused by the failure of the steering on the Brazilian champion’s Williams FW16.
To support this theory, prosecutor Maurizio Passerini appointed Professor Enrico Lorenzini, dean of the Faculty of Engineering at the University of Bologna, as expert consultant. Lorenzini ordered that the shaft be analyzed by two independent expert teams from different institutions, so that results could be compared and leave no room for doubt.
One part of the analysis was carried out by the Air Studies, Research and Testing Division of the Italian Air Force, based in Pratica di Mare, and the other by the Metallurgy Laboratory of Industrial Chemistry at the University of Bologna. Both groups had access to SEM—the Scanning Electron Microscope—the most advanced tool available at the time. Their findings matched, and they reached a single conclusion: Senna’s steering column failed before hitting the Tamburello wall and was the cause of the crash.
Thirty years later, I managed to contact Gian Paolo Cammarota and Angelo Casagrande, the two professors from the Bologna university who carried out the analysis. They are still friends and see each other from time to time. Cammarota, born in 1936 in Milan, now retired, divides his time between Bologna, Venice, and Germany. Slender and very reserved, he weighs every word. He was a pillar of Industrial Chemistry, while Casagrande, a true Bolognese, a lean but sturdier physicist, is still part of the Metallurgy faculty: “We’re currently decommissioning the SEM: now there are much more modern and advanced investigative systems, but the scanning electron microscope gave us clear, indisputable answers in the Senna case.”
Before discussing the metallurgical tests performed on the column, Gian Paolo Cammarota shares an interesting anecdote: “I had seen the accident on TV and, when I heard Senna had died and that his body would be transferred from Ospedale Maggiore to the Institute of Forensic Medicine on Via Irnerio, I felt the urge to go see for myself. I can’t explain why, and I certainly didn’t imagine I’d later be called to assess the very column. I didn’t see Senna’s body. I entered the ground floor and found technicians in Williams uniforms: they told me Ayrton was a great driver, but that weekend he had changed tires more often than usual because he felt vibrations, and that he wasn’t happy with the setup when he lined up for the race. The tires had nothing to do with it. I believe it was the column causing the vibrations, not the tires. But I would only realize that months later…”
The original design of the Williams FW16 included a single-piece steering column. However, Senna repeatedly complained to the Didcot-based team’s engineers that he couldn’t mount his usual steering wheel—used during his McLaren years—because his knuckles scraped against the top of the cockpit, causing painful abrasions. Senna thus insisted on having the column lowered to improve his driving position. This wasn’t easy, as the regulations required that once the wheel was removed, a 250×250 mm template had to be able to pass through the cockpit area to comply with 1994 FIA rules.
“Reducing the tube’s diameter was a major design error,” Cammarota adds. “Initially, it was a single-piece column that was later modified into three sections joined by welding. The chemical and mechanical tests showed the parts were made of different materials.”
What tests did you perform?
“We did a surface metallographic analysis, then checked internal and external roughness, and conducted a fractographic exam. The chemical analysis was done by Cermet. In Professor Lorenzini’s report submitted to the court, it says: ‘Generally speaking, the three-piece column is a sign of a poorly designed modification, as the slenderness of the section right at the point of maximum stress, the abrupt change in section with too small a radius, and the scratches caused by drilling and turning operations all contribute to structural weakness and significant risk of failure under static and dynamic fatigue loads. Notably, on the outer and inner surfaces of the joint, just below the fracture surface, clear circular tool marks are visible, showing a surface finish not suitable for components subjected to fatigue under extreme test conditions.’”
The original column consisted of a 910.2 mm metal tube, measured from the connection to the steering rack to the steering wheel hub. At 685.5 mm from the lower end (rack), the column was connected to the chassis via an aluminum bracket with a self-lubricating Teflon-type bushing, so the remaining 224.7 mm was overhanging.
The modified tube was made of three parts, with different materials and sections: the first part, made of T45 steel, went from the steering rack to the support and was 685.5 mm long, with an external diameter of 22.225 mm and a thickness of 0.9 mm; the second part, made of EN 14 steel, was 32 mm long after the intermediate support and toward the wheel, with a diameter of 18 mm and a thickness of 1.2 mm. This section was hollowed out from solid stock using a lathe; the third part, 193 mm long, was connected to the steering wheel and had the same specs as the first. The three sections were welded together.
Let’s clarify the numbers a bit: could human error have occurred during welding?
“I exclude that,” says Cammarota. “I showed our images to Professor Herold from the University of Magdeburg, a top expert in the field, and he assured me the welds were perfect. The problem was the reduced tube section exactly at the point of greatest stress.”
So why did the steering column fail?
“It was already cracked before the start of the GP,” explains Casagrande. “In short, there was a crack [a thin surface fracture that precedes failure in metallurgy, ed.] that had started before the race in which Senna died. The presence of oxide didn’t allow us to determine when the fatigue began, but it was enough to understand what had happened.”
Are you saying a tube was installed that should never have been used?
“Absolutely! Materials have a remarkable feature: they never lie. The mechanisms of these failures and the material’s exposure time matched perfectly with what happened. We can try to manipulate things, but metals are like… scripture.”
In F1, the best materials are usually used—what might have gone wrong?
“They made an unplanned modification. The stem dimensions and overhang were such that even with a super material, it might have lasted one more race. Then it would have failed unless replaced, because it couldn’t handle the stress. There’s no point blaming the material: that was a compounding factor, but given the dimensions and the component’s properties, that metal wouldn’t have withstood much more anyway.”
How long did you have the column?
“Less than a week, then we returned it,” specifies Cammarota. “Just enough time for SEM analysis: engineer Danesi, representing Williams, was always present during the tests. Initially, the British team didn’t want to hear about fatigue failure, but we immediately saw the break and had to assess how much of the rupture was due to fatigue and how much to tearing. When Didcot accepted the fatigue explanation, they claimed the car would’ve still been drivable even with 50% of the column circumference broken. Sure, it would’ve been—if Imola had been a straight line! But that wasn’t the case. Understandably, they tried a defense strategy, but the numbers were clear.”
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