Equiavlent Was Both Foreseeable and Not Tangential

Honeywell International, Inc.v. Hamilton Sundstrand Corporation [2006-1602] (April 18, 2008) [RADER, Newman, Dyk] The Federal Circuit affirmed the decision that prosecution history barred Honeywell from asserting the doctrine of equivalents.
SIGNIFICANCE: It is difficult to rebut the application of prosecution history estopper
BRIEF: The principal issues is whether Honeywell could rebut the presumption that rewriting a dependent in independent form barred application of the doctrine of equivalents. Honeywell could only do so by demonstrating that (1) the alleged equivalent would have been unforeseeable at the time of the narrowing amendment,” or (2) "the rationale underlying the narrowing amendment bore no more than a tangential relation to the equivalent in question," or (3) "that there was 'some other reason' suggesting that the patentee could not reasonably have been expected to have described the alleged equivalent." LOF: Prosecution history estoppel is a legal question subject to de novo review on appeal.
Regarding forseeability, the Federal Circuit noted that “[a]n equivalent is foreseeable if one skilled in the art would have known that the alternative existed in the field of art as defined by the original claim scope, even if the suitability of the alternative for the particular purposes defined by the amended claim scope were unknown.” The Federal Circuit explained the foreseeability requirement:
The principle of foreseeability ties patent enforcement appropriately to patent acquisition. In making this connection, foreseeability reconciles the preeminent notice function of patent claims with the protective function of the doctrine of equivalents. Thus, foreseeability in this context ensures that the doctrine does not capture subject matter that the patent drafter could have foreseen during prosecution and included in the claims. The goal of the principle is to ensure that the claims continue to define patent scope in all foreseeable circumstances, while protecting patent owners against insubstantial variations from a claimed element in unforeseeable circumstances. The foreseeability principle thus relegates the doctrine of equivalents to its appropriate exceptional place in patent enforcement.
The Federal Circuit said that to maintain consistency, a court must use the same definition of the equivalent to evaluate both foreseeability and infringement. The Federal Circuit said that Foreseeability does not require that the accused infringing product or process be foreseeable, nor that any equivalent exist at the time; rather foreseeability only requires that one of ordinary skill in the art would have reasonably foreseen the proposed equivalent at the pertinent time.
Turning to tangential, the Federal Circuit first noted that the tangential relation criterion for overcoming the Festo presumption is very narrow. To rebut the estoppel presumption with tangentiality, a patentee must "demonstrate that the rationale underlying the amendment bore no more than a tangential relation to the equivalent in question," or, in other words, that "the narrowing amendment was peripheral, or not directly relevant, to the alleged equivalent." Additionally, the reason for the narrowing amendment "should be discernible from the prosecution history record . . . ." If the prosecution history reveals no reason for the narrowing amendment, the presumption is not rebutted. The Federal Circuit said that the record shows that Honeywell made the amendment to add the limitation. Because the alleged equivalent focuses on the added limitation, the amendment bore a direct, not merely tangential, relation to the equivalent. Tangentiality does not help Honeywell overcome the presumption of surrender.