(CNN) -- Just days after a Boeing 737 flown by Southwest Airlines made an emergency landing with a hole in its fuselage, the Federal Aviation Administration said in a press release Monday that it will mandate operators of about 175 specific older Boeing 737s to conduct inspections for wear and tear.
The FAA said the "emergency directive" it plans to issue on Tuesday would affect about 80 U.S.-registered 737-300s, 737-400s and 737-500s, mostly operated by Southwest. The remaining 95 or so aircraft are registered outside the United States. Each of the 175 or so planes in question have taken off and landed more than 30,000 times and will receive repetitive electromagnetic inspections at regular intervals for fatigue damage.
In a separate statement, Boeing said it was working with the FAA, the National Transportation Safety Board and Southwest, and it was preparing a service bulletin to recommend lap joint inspections on certain 737 models.
NTSB board member Robert Sumwalt said Monday that inspectors have visually checked lap joints in the past, but haven't used high-tech monitoring, because no one thought that part of the plane was susceptible to cracks. Moving forward, inspectors will test the joints with an electromagnetic process.
The chairman on the U.S. Senate Committee on Commerce, Science and Transportation said in a statement that the American public wants answers to retain confidence in commercial air travel.
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"As the details of this unusual incident unfold, we will get a better understanding of what caused the plane's fuselage to tear open," said Sen. Jay Rockefeller, D-West Virginia. "I expect the FAA to be painstakingly diligent in reviewing the safety of all aircraft, and to conduct a careful investigation into what caused the cracks that have been discovered on the bodies of these planes."
Rockefeller took advantage of the occasion to renew his call for reauthorizing the FAA.
"The FAA reauthorization bill now headed to conference takes steps to strengthen the inspection process of passenger aircraft, and I hope we can move that bill quickly to a resolution," he said.
After Southwest canceled about 600 flights over the weekend to accommodate inspections, the airline said it canceled another 70 flights on Monday.
By 3:30 p.m. Monday, the company had checked out 67 of the 79 planes it had grounded for inspection. Southwest said 64 of the 737-300s were being returned to service, while inspectors had discovered subsurface cracks on three jets. Those three will remain out of service "until Boeing recommends an appropriate repair," Southwest said.
As planes are cleared, they will be put back into service, Southwest said. Inspections are expected to be completed by late Tuesday.
The airline recommended that customers should check with the website SWA.com for the status of a particular flight or rebook a trip before heading to the airport.
Eighteen minutes into Flight 812 from Phoenix to Sacramento, California, on Friday, a hole 5 feet long and 1 foot wide opened in the fuselage, causing the cabin to lose pressure, the NTSB said.
One flight attendant received minor injuries, the agency said.
The pilot initially planned to return to Phoenix, but he made an emergency landing at a military base in Yuma, Arizona, after flight attendants reported seeing blue sky through the jet's roof, the safety board's Robert Sumwalt told reporters.
Some of the 118 passengers who were aboard the crippled Boeing 737 said they feared for their lives.
"We were in shock," passenger Debbie Downey said Saturday. "We were in row 16, and my husband and I could see blue sky ... the wiring, the cabling. It actually was terrifying."
Greg Hansen said fellow passengers panicked and screamed as the sun shone through the cabin.
"Most people were just white knuckles, holding on to the arm rests," he said.
The airline said it provided a full refund, an apology and two complimentary round-trip passes on the airline for future flights.
In July 2009, another Southwest Airlines 737-300 made an emergency landing when cabin pressure dropped because of a football-size hole in the jet. That incident prompted the airline to inspect its entire fleet of 737-300s.
Earlier that same year, the airline was fined $7.5 million by the FAA after the agency found that Southwest operated 46 of its Boeing 737s on nearly 60,000 flights without performing mandatory inspections for fatigue cracks in their fuselages.
Sumwalt said the 737 used for Flight 812 had a maintenance check in March at Southwest's Dallas facility, and the jet had no outstanding maintenance issues at the time of the accident, with all its records "positive, up to date, (and) with no discrepancies."
The plane's flight data recorders had no noteworthy information on them, Sumwalt said.
CNN's Mike Ahlers, Ric Ward and Marnie Hunter contributed to this report
