WASHINGTON -- The Federal Aviation Administration is ordering $5 million in new inspections for Boeing 737s in response to a hole larger than a football that was torn in the roof of an aging Southwest Airlines plane during a flight in July 2009.

The order, which will be published Wednesday in the Federal Register, calls for repetitive inspections for cracking in the top of the fuselage of 109 planes in the 300, 400 and 500 series. Most of these models are flown by Southwest in the U.S.

The more-thorough inspections for those planes are projected to cost up to a total of $5.2 million, and additional repairs could cost $17,765 per plane, according to the FAA.

In a statement Monday, the FAA says the agency "always evaluates the effectiveness of our safety improvements." The latest directive is "to reduce risk further and assure continued safe operation," the agency says.

The FAA reported no incidents involving the same fixtures since 2009 and the manufacturer, Boeing Co., completed hundreds of inspections worldwide "with few findings," according to a company spokesman.

"This is part of the long-standing process through which airplane manufacturers, operators and regulators work together to continue the safety of the world's jetliners at the highest levels," says Miles Kotay, a Boeing spokesman.

The directive is the third of four that FAA is developing in response to the 2009 incident involving Southwest flight 2294 from Nashville to Baltimore, which made an emergency landing in Charleston, W.Va.

This incident was similar to Southwest flight 812 from Phoenix to Sacramento that made an emergency landing in Yuma, Ariz., in April 2011 after a 5-foot hole opened in the roof of that plane. However, the 2009 incident involved a different kind of joint than the one involved in the skin peeling back in the 2011 incident.

Both Southwest flights landed without serious injuries. But safety inspectors take the problem seriously because crewmembers and passengers can be sucked out of planes, which are pressurized like balloons in flight, if they decompress suddenly.

"With frequent pressurization with the aircraft going up and down in cycles, eventually there will be some fatigue that will set in," says Kevin Hiatt, president of the Flight Safety Foundation. "That's why they're taking extra precautions to take a look at this again."

In the Charleston incident, a triangular hole measuring 17.4 inches by 11.5 inches by 8.6 inches opened in the top of the plane near the tail, according to the investigation by the National Transportation Safety Board. The 737-300 had been through more than 42,000 flights at that point.

Passengers were startled by a loud bang and could see through the hole that opened in the ceiling at 34,000 feet. Air masks dropped for people to breathe before the pilot landed quickly.

FAA says the latest order was prompted by additional reports of cracking in joints around the crowns of planes. The goal is to "detect and correct fatigue-cracking of the fuselage skin, which could cause the fuselage skin to fracture and fail, and result in rapid decompression of the airplane."

The order calls for one of several types of microscopic inspections of the planes, in an effort to find flaws without actually taking the planes apart. The directive also calls for repetitive inspections of loose fasteners, with replacements as necessary. And the order also calls for installation of straps that reinforce sections of the fuselage skin.

"Airplanes are very, very well engineered," says Hiatt of the Flight Safety Foundation. "Fortunately, we have a process in place with air worthiness directives where we can head off problems before they begin."

While the Southwest passengers landed safely, others haven't been as lucky when planes decompress in flight:

-- Feb. 24, 1989, nine people were sucked out of a United Airlines 747 when its cargo door broke loose after taking off from Honolulu.

-- April 28, 1988, Flight attendant C.B. Lansing was thrown from an Aloha Airlines 737-200, which investigators say nearly broke apart.

--Dec. 22, 1980, two passengers died when a Saudi Arabian Airlines Lockheed L-1011 suffered decompression near Qatar because a wheel on the landing gear exploded, ripping a hole in the bottom the plane.

--Nov. 3, 1973, a passenger was sucked out the shattered window of a National Airlines Douglas DC-10 when its engine exploded near Albuquerque.

USA Today