Frontier Airlines, Dave Siegel, is resigning immediately, citing personal reasons. His departure comes two days after the government said Denver-based Frontier had the highest complaint rate and the worst on-time performance among the nation's 14 leading airlines in March.
Siegel has led Frontier since January 2012, as it shifted to an ultra-low-cost carrier model with low base fares but additional fees for many services.
The U.S. Department of Transportation says it received more complaints from people flying in March than it did in either the previous month or March of 2014. Passengers on Frontier Airlines were 34 times more likely to complain than passengers on Southwest Airlines, which has the lowest complaint rate. Spirit Airlines has the second-worst rate.