NTSB Cites 'A Chemically Milled Step' In Airplane Depressurization | Aero-News Network
Aero-News Network
RSS icon RSS feed
podcast icon MP3 podcast
Subscribe Aero-News e-mail Newsletter Subscribe

** Airborne 08.25.14 ** HD iPad-Friendly -- Airborne 08.25.14 **
** Airborne 08.22.14 ** HD iPad-Friendly -- Airborne 08.22.14 **
** Airborne 08.20.14 ** HD iPad-Friendly -- Airborne 08.20.14 **

Sat, Aug 21, 2010

NTSB Cites 'A Chemically Milled Step' In Airplane Depressurization

"Preexisting Fatigue" Named As Probable Cause For A Hole Opening In A Southwest Airlines 737

The NTSB says "fuselage skin failure due to preexisting fatigue at a chemically milled step" is the probable cause for a 18x12 inch hole opening up in the roof of a Southwest Airlines 737 last year, causing the airplane to depressurize. No one was injured due to the incident.

NTSB Identification: DCA09FA065
Scheduled 14 CFR Part 121: Air Carrier operation of SOUTHWEST AIRLINES CO
Accident occurred Monday, July 13, 2009 in Charleston, WV
Probable Cause Approval Date: 8/18/2010 1:52:06 PM
Aircraft: BOEING 737, registration: N387SW
Injuries: 131 Uninjured.

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.


NTSB Photo Exterior Skin

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.


NTSB Photo Interior Skin

The airplane, serial number 26602, was delivered to SWA in June 1994. At the time of the SWA event, the airplane had accumulated approximately 42,500 cycles and 50,500 hours.

FMI: www.ntsb.gov

Advertisement

More News

Airborne 08.25.14: SpaceX Setback, AMA Fights FAA, Redbird Migration 2014

Also: Copperstate Fly-In, No-Fly List Changes, Volcano Alert, Inhofe Campaigns In RV-8 In an initial report, ANN space correspondent, Wes Oleszewski, said that on the evening of Au>[...]

Aero-TV: In The Nick Of Time? - A NextGen GA Fund Update

The GA World Needs All The Help It Can Get... IF It Can Get It A hot topic at EAA AirVenture 2014 was the subject of the FAA requirement to be ADS-B equipped by January 1, 2020. In>[...]

ANN's Daily Aero-Linx (08.27.14)

International Republic Seabee Owner's Club (IRSOC) A website dedicated to the Seabee seaplane. You can find information about the airplanes and events, and talk to other Seabee ent>[...]

ANN's Daily Aero-Term (08.27.14): GPS Approach Overlay Program

An authorization for pilots to use GPS avionics under IFR for flying designated existing nonprecision instrument approach procedures, with the exception of LOC, LDA, and SDF proced>[...]

Aero-News: Quote Of The Day (08.27.14)

“We are grateful to Bruce for his years of unparalleled dedication to general aviation, and are delighted that he has agreed to continue on as our senior safety advisor.&rdqu>[...]

blog comments powered by Disqus



Advertisement

Advertisement

Podcasts

Advertisement

© 2007 - 2014 Web Development & Design by Pauli Systems, LC