In a statement, the airline said it discovered an overdue required maintenance check for the standby hydraulic system.
The carrier said it identified 182 aircraft that had overflown the check. It voluntarily removed the jets from service, began the maintenance checks, and disclosed the matter to the FAA.
The airline said the grounding resulted in about 80 flight cancellations on Tuesday.
Managers anticipate what they call “very minimal impact” on operations Wednesday.