Southwest Airlines Boeing 737 fuselage skin rupture: NTSB final report

by B. N. Sullivan

The U.S. National Transportation Safety Board (NTSB) has released its final report regarding the Southwest Airlines Boeing 737-300 that developed a hole in its fuselage during flight on July 13, 2009.  According to the NTSB report, the probable cause of this accident was, "Fuselage skin failure due to pre-existing fatigue at a chemically milled step."

At the time of the accident, the aircraft (registration N387SW) was en route from Nashville International Airport (BNA) to Baltimore-Washington International Airport (BWI), operating as Southwest Flt WN2294.  A hole in the crown of the aircraft's fuselage developed when the skin ruptured just forward of the vertical stabilizer.  When the  hole opened, the cabin depressurized.  The crew diverted to Charleston, WV where they made a safe emergency landing at Yeager Airport (CRW).  No one was injured.

Quoting from the summary of the NTSB report:

Flight data recorder data revealed that the airplane took off and climbed for about 25 minutes to an altitude of approximately 35,000 feet, at which point the cabin altitude warning activated, and the captain disengaged the autopilot. Postincident examination of the airplane revealed fatigue cracking of the fuselage skin near the leading edge of the vertical stabilizer adjacent to the rupture. The fatigue cracking penetrated the fuselage skin and created an approximate 18-inch by 12-inch flap in the skin that depressurized the airplane.

The fuselage skin assembly near the leading edge of the vertical stabilizer was manufactured by bonding two full aluminum sheets together, then selectively chemically milling away pockets (bays) of the inner sheet. Continuous fatigue cracks initiated from multiple origins on the inner surface of the skin adjacent to the step formed at the edge of the chemically milled area and propagated outward.

Following the Southwest Airlines (SWA) flight 2294 event, on September 3, 2009, Boeing issued Service Bulletin (SB) 737-53A1301, calling for repetitive external inspections to detect cracks in the fuselage skin along the chemically milled step at stringers S-1 and S-2 right and between BS 827 and BS 847. (The hole from the SWA event was within those boundaries.) If cracks are detected, operators are to contact Boeing for repair instructions. On January 12, 2010, the Federal Aviation Administration issued Airworthiness Directive 2010-01-09, which mandated the inspection requirements in SB 737-53A1301.

Note:  The photos on this page were released by the NTSB In July of 2009.  The first photo (top of this page) shows the section of fuselage skin facing inside the aircraft.  The second photo shows the section of fuselage skin on exterior of aircraft.  Clicking on either photo will take you to a larger version on the NTSB website.

Links to the NTSB report [NTSB ID DCA09FA065]:  Summary /  Full Narrative

RELATED:

• Southwest Airlines Boeing 737 with hole in fuselage lands safely at Charleston, WV - Jul 13, 2009
• NTSB Photos: Damaged section of Southwest Airlines B737-300 - Jul 16, 2009

NTSB Photos: Damaged section of Southwest Airlines B737-300

by B. N. Sullivan

The U.S. National Transportation Safety Board (NTSB) has just released two photos from their investigation of the Southwest Airlines Boeing 737-300 cabin depressurization incident on July 13, 2009. The aircraft (registration N387SW), which had been en route from Nashville to Baltimore-Washington International Airport, diverted to Charleston, WV where it made a safe emergency landing. A hole in the crown of the fuselage apparently led to the depressurization.

The two photos released by the NTSB today show "the compromised section of the area of the fuselage that failed in flight."

The first photo (top of this page) shows the section of fuselage skin facing inside the aircraft. The second photo shows the section of fuselage skin on exterior of aircraft.

The press release accompanying the release of the photos said, in part:

The damaged aircraft skin section was visually examined in the NTSB's Materials Laboratory. The damage left a hole measuring approximately 17 inches by 8 inches. The skin in this area of the fuselage is 0.032 inches thick with an additional 0.032 inch thick layer bonded to the interior surface in selected areas.

[ NTSB Acting Chairman] Rosenker said that the initial visual examination found the fractures in good condition and suitable for further analysis. No significant corrosion or obvious pre-existing mechanical damage was noted. A detailed metallurgical examination of the skin section and the fracture surfaces will be accomplished by the Safety Board in the coming days.

Southwest Airlines is now in the process of repairing the aircraft at Yeager Airport, Charleston, West Virginia.

You can click on either of the photos to obtain a larger copy from the NTSB web site.


[Photo Source]

Southwest Airlines B737 with hole in fuselage lands safely at Charleston, WV

by B. N. Sullivan

A Southwest Airlines Boeing 737-300 aircraft made an emergency landing at Yeager Airport, Charleston, WV today after a hole in the fuselage caused a loss of cabin pressure. The aircraft, operating as Southwest Flight SWA 2294, was en route from Nashville International Airport to Baltimore-Washington International Airport at the time of the incident. The crew diverted to to Charleston, where the plane landed at about 6PM local time. There were no reports of injuries among the five crew members and 126 passengers on board.

Reporting on the incident, the Charleston Gazette quoted a passenger from the flight:

"We heard a loud pop, and one of the panels [on the ceiling] was sucked up tight against the ceiling. You could definitely tell there was a hole there."

Oxygen masks dropped from the ceiling, and passengers put them on. "The flight attendants did a wonderful job, walking back and forth and keeping everyone calm," he said.

The plane remained in the air for 20 to 30 minutes, [passenger] Hall estimated, before landing at Yeager. "It felt like a long time," he said.

The passenger described the hole as "about the size of a football," and said that a "piece of the roof was kind of peeled back."

A brief article about the incident on the WSMV.com web site included a photo of the hole, taken from inside the aircraft by a passenger. It definitely looks as though the hull was breached -- you can see daylight through the hole in the photo!

At this point, no one seems to know what caused the damage. Should more information become available, I will post an update here on Aircrew Buzz.

UPDATE: Another photo has emerged, via Twitter user @cjmcguinness. He says this photo was taken by his sister-in-law, who was a passenger on the flight.

A representative of Southwest Airlines has posted the following statement on FlyerTalk.com:

SOUTHWEST AIRLINES PROVIDES INFORMATION REGARDING FLIGHT 2294

Scheduled Nashville-Baltimore Flight Diverts to West Virginia

DALLAS, TX—July 13, 2009--Southwest Airlines confirms its flight 2294, the 4:05 pm Eastern scheduled departure from Nashville to Baltimore/Washington diverted into Yeager Airport in Charleston, W. Va at approximately 6:10 pm Eastern today after a cabin depressurization. All 126 passengers and crew of five onboard landed safely and are awaiting a replacement aircraft in Charleston that will take them to Baltimore Washington International Airport later this evening.

The aircraft cabin depressurized approximately 30 minutes into the flight, activating the passengers’ onboard oxygen masks throughout the cabin. Medical personnel in Charleston assessed passengers and no injuries are reported. Southwest is sending its maintenance personnel to Charleston to assess the aircraft, and the airline will work with the NTSB to determine the cause of the depressurization. According to initial crew reports, the depressurization appears to be related to a small hole located approximately mid-cabin, near the top of the aircraft.

Thanks to Twitter user @danwebbage for providing the link to this statement.

UPDATE July 14, 2009: This morning the U.S. National Transportation Safety Board (NTSB) issued an advisory announcing the dispatch of a team to investigate the Southwest Flight 2294 decompression incident. In that advisory, the NTSB identified the aircraft as N387SW. The FAA Registry data for that registration number lists the aircraft model as a Boeing 737-3H4, serial no. 26602, manufactured in 1994.

A new photo published by The Charleston Gazette shows an individual described as an FAA Inspector peering at the damage to the fuselage from outside the aircraft. In that photo, the damaged area appears to be at the crown of the hull, just forward of the empennage.

The track log for the accident flight on FlightAware.com, which is based on an FAA data feed, suggests that the aircraft was above FL340 ad climbing at about the time of the decompression, traveling at a ground speed of about 450 kts.

UPDATE July 16, 2009: The NTSB has released two photos of the damaged section of the fuselage of the Boeing 737-300.