CHARLOTTE, N.C. -- Evidence mounted Monday that airlines, which are considered a lagging indicator of the economy, had a disappointing March.

JetBlue ( JBLU) said Monday that its passenger revenue per available seat mile decreased 12% in March. While capacity decreased by 5.6%, the number of revenue passenger miles decreased by 8.5%, JetBlue said.

Meanwhile, Delta ( DAL), the world's largest airline, said that while its capacity fell by 7.9%, its revenue passenger miles fell by 12.6%. Delta does not report PRASM on a monthly basis.

Last week, US Airways ( LCC) said its March PRASM fell by 17% to 19%. "Our March traffic results reflect the Easter holiday shift from March in 2008 to April in 2009 as well as a reduction in travel that we, like the rest of the industry, experienced during the month," said President Scott Kirby, in a prepared statement.

In response, Jesup & Lamont analyst Helane Becker reduced her first-quarter estimates for US Airways, estimating a loss of $2.50 a share. Analysts surveyed by Thomson Reuters are estimating a loss of $2.10 for the quarter.

"Although fuel costs were lower than we were anticipating, it wasn't enough to offset the estimated 17% decline in passenger revenues," Becker wrote. "Ancillary revenues are estimated to be up by 19% in the quarter, also not enough to offset the decline in passenger revenues (9% of total revenues)."

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