In affirming a district court's holding that the patentee failed to rebut the presumption of prosecution history estoppel, the U.S. Court of Appeals for the Federal Circuit rejected the patentee's argument that, because the equivalent was not developed by the alleged infringer until years after the patent issued, the alleged equivalent was unforeseeable at the time of the patent's prosecution. Honeywell Int'l, Inc. v. Hamilton Sundstrand Corp., Case No. 06-1602 (Fed. Cir., April 18, 2008) (Rader, J.; Newman, J., dissenting).
Honeywell's patents at issue relate to auxiliary power units (APUs), which are gas turbine engines used in aircrafts. The patents claim technology that prevents airflow from surging back into the engine's compressor, thereby averting damage to the APU.
Honeywell accused Sundstrand's APU device of infringement. In an earlier decision in this litigation, the Federal Circuit vacated the jury's verdict that Sundstrand infringed the patents under the doctrine of equivalents because the Court found that the patentee's "rewriting of dependent claims into independent form coupled with the cancellation of the original independent claims creates a presumption of prosecution history estoppel." Prosecution history estoppel prevents a patentee from recapturing under the doctrine of equivalents subject matter surrendered during prosecution to obtain a patent. As a result, Honeywell would only be permitted to assert infringement under the doctrine of equivalents if it rebutted the presumption of prosecution history estoppel.
Under Festo, the presumption of estoppel can be rebutted, inter alia, by demonstrating (as Honeywell attempted here) that the alleged equivalent was unforeseeable at the time of the amendment. The alleged equivalent was that Sundstrand's APU devices used the position of inlet guide vanes (IGVs) to detect high flow and low flow. On remand, the district court found that the alleged equivalent was foreseeable and thus barred Honeywell from asserting the doctrine of equivalents. Honeywell appealed.
On appeal, Honeywell argued that the alleged equivalent was unforeseeable because surge control systems did not use IGVs to ascertain the existence of high or low flow situations during the relevant time period. Honeywell also pointed to the fact that Sundstrand did not develop the alleged equivalent until years after the relevant amendments. The Court rejected Honeywell's arguments because "the mere temporal relationship" of the equivalent to the amendment process does not make the equivalent unforeseeable.
The Court emphasized that "foreseeability only requires that one of ordinary skill in the art would have reasonably foreseen the proposed equivalent at the pertinent time." In affirming the finding that the equivalent was foreseeable, the Court cited prior art which showed that it was known that surge control was important; IGVs were routinely used in surge control systems; and IGVs affected the air flow rate. In addition, the Court noted that the district court determined that Sundstrand's expert was credible. Thus, the Court found no clear error in the district court's conclusion that the use of IGVs to detect high flow and low flow was foreseeable. Thus, Honeywell should have drafted claims to encompass this foreseeable equivalent during prosecution.
It is apparent that the Court intends to use the foreseeability principle to limit the application of the doctrine of equivalents. The Court stated, "The foreseeability principle thus relegates the doctrine of equivalents to its appropriate exceptional place in patent enforcement."
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