A radical measure to immediately check engines follows a mid-air explosion last week.
Southwest Airlines has begun ultrasonic inspections of its engines, covering almost its entire fleet of more than 700 planes, following the mid-air explosion last week that killed a passenger.
The Dallas-based carrier cancelled 40 flights over the weekend and 129 more on Monday as it checks the fan blades on all of its CFM56 engines over the next 30 days, the LA Times reports.
Southwest says that about 1% to 2% of its flights will be disrupted over the next few days as it continues the inspections.
The radical measure exceeds the requirements of an emergency airworthiness directive issued by the US Federal Aviation Administration on Friday.
This order requires all airlines to inspect the fan blades of CFM56-7B engines, manufactured by CFM International, a joint venture between General Electric and Safran Aircraft Engines, which are used to power 737 Next Generation planes.
CFM and the FAA recommend that such engines with more than 30,000 takeoff-and-landing cycles must be inspected. For engines with 20,000 cycles, inspection is urged by the end of August. For all other engines, inspections are recommended on reaching 20,000 cycles.
Around 14,000 CFM56-7B engines are in operation, according to CFM, and the fan-blade inspections recommended within the next 20 days will affect about 680 engines.
More than 150 have already been checked, and inspections recommended by the end of August will affect an additional 2,500 engines.
United and American
United Airlines operates 547 Boeing 737s with CFM engines, according to Boeing. It has also begun inspections of the engines.
American Airlines operates 305 Boeing 737s powered by CFM56 engines. The airline says that none of these have experienced 30,000 cycles and so are not yet required to be inspected.