## Facts

- Spirit, a low-fare “no frills” airline, began service from Detroit to Boston and Philadelphia to attract price-sensitive leisure travelers.
- Northwest was the dominant carrier at Detroit Metropolitan Airport, with a majority share of passengers and control over most airport gates, creating entry barriers.
- Spirit alleged Northwest responded by substantially increasing capacity and offering very low fares on overlapping routes targeted at leisure travelers, with some fares priced below cost.
- Spirit asserted that after Spirit exited the contested routes, Northwest raised its lowest fares to levels higher than its pre-entry prices.
- Spirit brought claims for monopolization and attempted monopolization under § 2 of the Sherman Act, relying primarily on a predatory-pricing theory focused on a low-fare/leisure passenger market segment.
- The district court granted summary judgment to Northwest, rejecting Spirit’s proposed leisure-passenger market, accepting a broader “all passengers” market, and concluding Northwest’s route-wide revenues exceeded route-wide costs.

## Issues

1. Whether, on summary judgment, a reasonable factfinder could find a relevant antitrust market limited to low-fare/leisure passengers on the Detroit–Boston and Detroit–Philadelphia routes.
2. Whether Spirit produced sufficient evidence of below-cost pricing and recoupment (and related § 2 elements) to proceed to trial on monopolization and attempted monopolization claims.
3. Whether the district court improperly resolved disputes in expert methodology and economic inferences that should have been left to the factfinder.

## Decision

- The Sixth Circuit reversed the grant of summary judgment for Northwest and remanded.
- The court held that, viewing the record in Spirit’s favor, a reasonable factfinder could find a distinct low-fare/leisure passenger market on the challenged routes.
- The court held a reasonable factfinder could also find predatory pricing in that market, including below-cost pricing and a plausible ability to recoup losses through later higher fares.
- The court concluded that disputes over market definition, cost measures, and competing economic analyses were fact-intensive and not properly resolved by weighing credibility on summary judgment.

## Legal Principles

- At summary judgment, courts must view evidence and reasonable inferences in favor of the nonmovant and may not weigh competing expert credibility or choose among contested economic methodologies.
- A relevant antitrust market may be a subset of customers (such as leisure or low-fare passengers) if record evidence supports distinct demand characteristics and competitive conditions for that group.
- Predatory pricing under Sherman Act § 2 generally requires evidence of pricing below an appropriate measure of cost and a plausible ability to recoup losses after disciplining or excluding a rival.
- Route-wide profitability based on aggregating all passengers may not defeat a predatory-pricing claim if the alleged predation is directed at, and measured within, a targeted customer segment.

## Conclusion

The Sixth Circuit held that Spirit presented triable evidence that leisure passengers constituted a distinct relevant market and that Northwest’s targeted low-fare conduct could qualify as predatory pricing with potential recoupment, making summary judgment improper and requiring further proceedings.


Spirit Airlines, Inc. v. Nw. Airlines, Inc., 431 F.3d 917 (6th Cir. 2005)