The airline said Tuesday night that it had canceled 90 flights so far. The grounding covers about one-fifth of its fleet.
Southwest spokeswoman Brandy King said that after discovering the missed inspections, the airline immediately notified federal safety regulators and began checking the planes.
A spokesman for the
The missed inspections were first reported by the Wall Street Journal.
King called the missed inspections inadvertent. She said the airline discovered that 128 of its Boeing 737-700 jets already had flown beyond the point at which the backup hydraulic systems were supposed to be inspected. She said safety was the airline's top priority, and it was working to fix the matter quickly.