Is A Patent Claim's Preamble Limiting? Following the Guideposts...

Enpat sued a number of entities (in separate cases) for infringing U.S. Patent No. 6,328,260, a patent related to a wing spar modification kit to be used for strengthening wings on certain amphibious airplanes.  Asking for claim construction, one defendant argued that the preamble of the first independent claim was limiting.  Enpat disagreed, arguing instead that the preamble merely recited an intended use.

The preamble of claim 1 reads:

A modification kit for retrofitting a wing spar on an amphibious airplane, said airplane having a root rib, and said wing spar comprising a wing-spar cap angle that is attached to a wing spar web, said wing spar web having an upper edge and a lower edge and an inboard end that attaches to said root rib, a first series of wing-attach bolt-holes that is provided in said upper edge and a second series of wing-attach bolt-holes that is provided in said lower edge of said wing spar web, wherein said root rib is angled relative to a vertical plane of said amphibious airplanes, and wherein said inboard end of said wing spar has an inboard-end angle that corresponds to an angle of said root rib, said modification kit comprising:

The Court recognized that no litmus test exists for determining whether or not a preamble is limiting.  Instead, a number of "guideposts" should be followed.  If the preamble merely describes "the use of an invention" while the body of the claim sets forth a "structurally complete invention," the preamble is not limiting.  But the preamble may be limiting if (1) the applicant clearly relies on it during prosecution as distinguishing the invention over the prior art; or (2) a particular disputed phrase within the preamble provides the antecedent basis for a limitation within the claim.

After laying out this law, the Court concluded that the '260 patent and its file history did not rely on the preamble language as a basis for distinguishing the invention from the prior art.  The defendant sought to capitalize on a scrivener's error in the claim body language.  The claim body referred to the limitation "said wing spar."  Defendant pointed to the preamble as the only antecedent basis for "wing spar."  While no qualm could be had with that statement, the Court saw through it:

While a cursory reading of claim 1 confirms [Defendant's] statement, a fair reading of claim 1 in the context of the entire Patent reveals that "said wing spar" in the body of claim 1 should read "said wing spar web."  Read without the scrivener's omission of "web," one need not resort to the preamble to find any antecedent basis for the "wing spar" referenced in the body of the claim.

Defendant's second approach was to point to limitations in dependent claim 10 that had their antecedent basis in the preamble.  Enpat agreed.  The Court thus found the preamble limiting only for claim 10 (and not the broader independent claim 1).

Enpat, Inc. v. Shannon, Case No. 6:11-cv-84 (M.D. Fla. Nov. 30, 2011) (J. Presnell)