OAKLAND (BCN) — At least five Southwest Airlines flights have been cancelled in the Bay Area today because of overdue, mandatory maintenance checks of hydraulic equipment on 128 of the airline’s 737-700 aircraft.

Southwest Airlines said in a statement that they discovered the overdue maintenance checks on the “standby hydraulic system, which serves as a back-up to the primary hydraulic systems” on Tuesday.

About 80 flights were cancelled nationwide Tuesday, according to Southwest. The airline said they’ve removed the affected planes from service.

Oakland International Airport spokesman Keoni Wagner said five Oakland flights had been cancelled Tuesday, with five more flights cancelled today.

San Francisco International Airport spokesman Doug Yakel said two Southwest flights have been cancelled today after three were cancelled Tuesday.

“That’s not outside of the norm,” Yakel said. “But I don’t know whether or not they were a direct result of this maintenance issue.”

Mineta San Jose International Airport spokeswoman Rosemary Barnes said no flights into or out of San Jose had been cancelled so far because of the maintenance checks.