In late March 2008 and again in early April 2008, an FAA safety audit of American Airlines forced the airline to ground all its MD-80 series aircraft (approximately 300) to inspect the wiring for one of the aircraft's hydraulic systems. This led to American canceling nearly 2,500 flights in March and over 3,200 in April. In addition, Delta Air Lines voluntarily inspected its own MD-80 fleet to ensure its 117 MD-80s were also operating within regulation. This resulted in Delta canceling 275 flights.