--- title: "Mechanical Engineering Expert Allowed to Opine on the Behavior of Wheelchairs" meta: "og:description": "The mechanical engineering expert was permitted to opine on stability, braking forces, and the consequences of a sudden stop" "og:title": "Mechanical Engineering Expert Allowed to Opine on the Behavior of Wheelchairs" author: "Expert Witness Profiler" description: "The mechanical engineering expert was permitted to opine on stability, braking forces, and the consequences of a sudden stop" --- # Mechanical Engineering Expert Allowed to Opine on the Behavior of Wheelchairs Posted on April 3, 2026 by Expert Witness Profiler This case arises from an incident in which Plaintiff William Dowdy was injured after falling from a temporary wheelchair while using his wheelchair ramp. The temporary wheelchair had been supplied by NuMotion while Dowdy’s regular wheelchair was being serviced and repaired. NuMotion sought to exclude the testimony of Plaintiff’s expert [Mark Ezra](https://expertwitnessprofiler.com/expert-witness/Mark-Ezra/1539674), arguing that he lacks the proper qualifications, that his opinions rest on speculation rather than reliable methodology, and that his testimony will not assist the jury. ## **Mechanical Engineering Expert Witness** [Mark A. M. Ezra](https://expertwitnessprofiler.com/expert-witness/Mark-Ezra/1539674) is a board-certified professional engineer with a degree in mechanical engineering and a diploma in automatic control systems. His professional background includes decades of engineering practice, mechanical failure analysis, and forensic investigation. [Want to know more about the challenges Mark Ezra has faced? Get the full details with our Challenge Study report](https://expertwitnessprofiler.com/order/add?eId=1539674&pId=3). ## **Discussion by the Court** ### _**Qualifications**_ NuMotion emphasized that Ezra is not a biomechanical engineer, has never worked for a wheelchair supplier, and has no experience as an Assistive Technology Professional (“ATP”). Mechanical engineering is directly relevant to the design, stability, braking systems, and mechanical behavior of powered wheelchairs—the very issues at the heart of this case. The Court therefore found that Plaintiff has shown by a preponderance of the evidence that Ezra is qualified to offer expert testimony. ### _**Reliability**_ NuMotion argued that Ezra’s opinions lack a factual foundation, that he improperly relied on the testimony of ATP Vincent Fels, and that he cannot identify the precise electrical defect that caused the wheelchair to stop. Ezra’s expert report reflected a systematic engineering analysis grounded in physical inspection, measurements, documentary review, and application of mechanical principles. He personally inspected the TSS 300 wheelchair, took custody of it, and measured the slope of Plaintiff’s ramp. He reviewed the owner’s manuals for both the TSS 300 and the Jazzy 600, analyzed their braking systems, and compared their wheel configurations and stability characteristics. Ezra considered Plaintiff’s prior successful use of both wheelchairs on the same ramp and applied simple Newtonian mechanics to explain how a sudden stop would eject a seated user. Based on this analysis, Ezra concluded that the “most probable and direct cause” of the incident was a power failure in the TSS 300’s electrical system, which triggered the automatic deployment of the parking brakes. NuMotion also contended that Ezra improperly relied on ATP Fels’ testimony to opine on warnings and training. But Ezra’s core opinions concern mechanical behavior like stability, braking forces, and the consequences of a sudden stop, not ATP standards of care. The Court concluded that his references to Fels’ testimony serve only to contextualize the absence of instruction and the differences between the two wheelchairs, not to substitute himself for an ATP. ### _**Relevance**_ NuMotion argued that Ezra’s testimony will not assist the jury because he cannot say whether NuMotion caused the defect or could have prevented it. But [Rule 702](https://www.law.cornell.edu/rules/fre/rule_702#:~:text=Rule%20702%20sets%20forth%20the,is%20a%20relatively%20narrow%20inquiry.) does not require an expert to resolve every element of liability. Ezra’s testimony will help the jury understand the mechanical forces at play, the behavior of the TSS 300 during braking, the significance of the design differences between the TSS 300 and the Jazzy 600, and the mechanical plausibility of Plaintiff’s account. These matters are well outside the knowledge of a lay juror. Whether NuMotion caused the defect is a separate question for the jury, informed by, but not dependent on, Ezra’s mechanical analysis. ## **Held** The Court denied NuMotion’s motion to strike the testimony of Mark Ezra. ## **Key Takeaway** This methodology of identifying possible mechanical causes, ruling out alternatives, and applying engineering principles to the physical evidence is consistent with accepted practices in mechanical failure analysis. The fact that Ezra cannot identify the specific electrical component that failed does not render his opinion unreliable. Experts are not required to pinpoint the exact microscopic failure mechanism where the available evidence supports a broader, scientifically grounded conclusion. Ezra’s reasoning is transparent, testable, and rooted in the materials he reviewed. ## **Case Details:** --- ## **You Might Also Like** ![Mechanical Engineering Expert Allowed to Opine on the Behavior of Wheelchairs](https://ewp-blog.expertwitnessprofiler.org/wp-content/uploads/2026/04/blog-pic-640X480-2026-04-03T203819.018.jpg) [**Mechanical Engineering Expert Allowed to Opine on the Behavior of Wheelchairs**](https://expertwitnessprofiler.com/mechanical-engineering-expert-allowed-to-opine-on-the-behavior-of-wheelchairs/mechanical-engineering-expert-allowed-to-opine-on-the-behavior-of-wheelchairs)![Insurance Expert Not Allowed to Opine on Industry Standards](https://ewp-blog.expertwitnessprofiler.org/wp-content/uploads/2026/04/blog-pic-640X480-2026-04-03T192250.590.jpg) [**Insurance Expert Not Allowed to Opine on Industry Standards**](https://expertwitnessprofiler.com/mechanical-engineering-expert-allowed-to-opine-on-the-behavior-of-wheelchairs/insurance-expert-not-allowed-to-opine-on-industry-standards)![Credit Reporting Expert Not Allowed to Opine on Intentions](https://ewp-blog.expertwitnessprofiler.org/wp-content/uploads/2026/04/blog-pic-640X480-2026-04-03T160159.490.jpg) [**Credit Reporting Expert Not Allowed to Opine on Intentions**](https://expertwitnessprofiler.com/mechanical-engineering-expert-allowed-to-opine-on-the-behavior-of-wheelchairs/credit-reporting-expert-not-allowed-to-opine-on-intentions)![Consumer Credit Expert Not Allowed to Opine on Policies](https://ewp-blog.expertwitnessprofiler.org/wp-content/uploads/2026/04/blog-pic-640X480-2026-04-03T135126.047.jpg) [**Consumer Credit Expert Not Allowed to Opine on Policies**](https://expertwitnessprofiler.com/mechanical-engineering-expert-allowed-to-opine-on-the-behavior-of-wheelchairs/consumer-credit-expert-not-allowed-to-opine-on-policies)![Marketing Expert Not Allowed to Opine on Consumer Reaction](https://ewp-blog.expertwitnessprofiler.org/wp-content/uploads/2026/04/blog-pic-640X480-2026-04-02T115237.879.jpg) [**Marketing Expert Not Allowed to Opine on Consumer Reaction**](https://expertwitnessprofiler.com/mechanical-engineering-expert-allowed-to-opine-on-the-behavior-of-wheelchairs/marketing-expert-not-allowed-to-opine-on-consumer-reaction)