Mechanical Engineering Expert Was Allowed to Opine on Slide Design

Plaintiff Slick Slide LLC (“Plaintiff” or “Slick Slide”) brought claims of direct and indirect patent infringement, as well as copyright infringement against the Defendants Edwin L. Reed, Trampoline Park Gurus, LLC, and Adventure Park Contractors, LLC (collectively, the “Reed Defendants”).

Slick Slide filed a motion to exclude the testimony of Defendants’ expert Nathan J. Macdonald.

Mechanical Engineering Expert Witness

Nathan James Macdonald is a registered Professional Engineer in the State of Utah. He is also a Certified Safety Professional in comprehensive practice. MacDonald is also a certified commercial building inspector. He received his Bachelor of Science degree in Mechanical Engineering from Brigham Young University in 2014. He has worked as a mechanical engineering consultant for Alpine Engineering & Design, Inc. for over 12 years.

Want to know more about the challenges Nathan Macdonald has faced? Get the full details with our Challenge Study report.

Discussion by the Court

Slick Slide challenged only Mcdonald’s qualifications, arguing that MacDonald is unqualified to serve as an expert.

Basically, Slick Slide argued that “Macdonald is not qualified to offer an opinion regarding obviousness” because he “has never designed a slide, the subject matter of the ‘821 patent, as well as the subject matter of both references that he suggests could be combined.” Slick Slide further argued that MacDonald is only a “general engineering consultant,” with limited engineering experience that fundamentally—and, from Slick Slide’s perspective, fatally—lacks slide design.

The Court agreed with Defendants that the record made it clear that MacDonald has the “necessary qualifications to testify as an ‘ordinary designer'” in this case. MacDonald is a registered Professional Engineer, with over twelve years of mechanical engineering consultant experience, and who has numerous relevant certifications and licenses. His professional experience includes “taking part in the design, manufacture, and review of numerous products, including ziplines, drop rides, slingshot rides, alpine slides, alpine coasters, roller coasters, water slides, rope swing slides, pendulum swing rides, and more.” He has served as the lead engineer on numerous projects, including “ziplines, exercise equipment . . . aerial lifts, and other hydraulic pneumatic, and electronic equipment,” and has extensive experience with amusement rides and devices.

Finally, to the extent that the exclusion motion challenged MacDonald’s specialized knowledge “with respect to the subject matter of this particular case—slides,” or the obviousness of the ‘821 patent, the Court held that questions regarding the extent of an expert’s specialized knowledge in a field go to the weight of the expert’s testimony, not to its admissibility.

Held

The Court denied Slick Slide’s motion to exclude the testimony of Defendants’ expert Nathan J. MacDonald.

Key Takeaway

As long as an expert stays within the reasonable confines of his subject area, a lack of specialization does not affect the admissibility of the expert opinion, but only its weight.

Case Details:

Case Caption:	Slick Slide Llc V. Reed
Docket Number:	1:23cv1649
Court Name:	United States District Court, Colorado
Order Date:	December 17, 2025