Southwest Airlines (LUV) - Get Report fell 4.79% to $57.78 Wednesday afternoon after the airline reduced the outlook for its first-quarter revenue per available seat mile, a key metric in the airline industry. 

Southwest said that its RevPAR would be flat year over year, down from its previous view of an increase between 1% and 2%. 

The Dallas-based airline blamed the lowered outlook on the timing of the spring break holidays, saying that the early start led to weaker travel demand than it had previously anticipated. 

Southwest's footprint overlaps most closely with United Continental Holdings Inc. (UAL) - Get Report  and the airline fell in conjunction with Southwest, declining 0.77% to $69.94. 

But United wasn't the only airline to suffer. 

JetBlue Airways (JBLU) - Get Report fell 2.33%, Delta Air Lines (DAL) - Get Report dropped 0.97% and Spirit Airlines (SAVE) - Get Report  declined 3.64%.