# NTSB DCA09FA065: Boeing 737, N387SW, Charleston, WV, July 13, 2009 - Type: NTSB accident investigation - Classification: Accident · No injuries · Field investigation · Final report - Date: July 13, 2009, 17:45 local (21:45 UTC) - Place: Charleston, WV - Coordinates: 38.373054, -81.593055 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=38.3731&lon=-81.5931&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute-cruise: Aircraft structural failure](https://openairdocs.org/ntsb-events/337) - Highest injury: No injuries - Injuries: 131 uninjured - Status: Completed, report August 18, 2010 - Report: Approved by Office Director - NTSB office: Major Investigations Division - Parties: FAA AAI-100 - ADs cited in the narratives: [AD 2010-01-09](https://openairdocs.org/ad/2010-01-09) (OpenAirDocs) - NTSB case key (mKey): 74266 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=DCA09FA065 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/74266/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=74266 - Page: https://openairdocs.org/ntsb/DCA09FA065 ## Probable cause Fuselage skin failure due to preexisting fatigue at a chemically milled step. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Fuselage: plates/skins (aux fuselage)](https://openairdocs.org/ntsb-findings/01035330): Aircraft › Aircraft structures · Fatigue/wear/corrosion (probable cause); cases with it: [Boeing 737-3H4, 1 case](https://openairdocs.org/ntsb-findings/01035330/cases.md?model=138447K), [All aircraft, 4 cases](https://openairdocs.org/ntsb-findings/01035330/cases.md) - [Fuselage: plates/skins (aux fuselage)](https://openairdocs.org/ntsb-findings/01035330): Aircraft › Aircraft structures · Failure (probable cause); cases with it: [Boeing 737-3H4, 1 case](https://openairdocs.org/ntsb-findings/01035330/cases.md?model=138447K), [All aircraft, 4 cases](https://openairdocs.org/ntsb-findings/01035330/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute-cruise: Emergency descent initiated](https://openairdocs.org/ntsb-events/130); cases with it: [Boeing 737-3H4, 1 case](https://openairdocs.org/ntsb-events/130/sequence.md?model=138447K), [All aircraft, 42 cases](https://openairdocs.org/ntsb-events/130/sequence.md) - [Enroute-cruise: Aircraft structural failure](https://openairdocs.org/ntsb-events/337) (defining event); cases with it: [Boeing 737-3H4, 2 cases](https://openairdocs.org/ntsb-events/337/sequence.md?model=138447K), [All aircraft, 290 cases](https://openairdocs.org/ntsb-events/337/sequence.md) ## Analysis 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. ## Factual narrative History of Flight On July 13, 2009, about 1745 eastern daylight time, Southwest Airlines (SWA) flight 2294, a Boeing 737-3H4 (737), N387SW, experienced rapid decompression while in cruise flight at approximately 35,000 feet when the fuselage crown skin ruptured just forward of the vertical stabilizer. Passenger oxygen masks deployed automatically. The flight crew declared an emergency, and the flight landed uneventfully at Yeager Airport (CRW), Charleston, West Virginia. The flight, which was on an instrument flight rules flight plan, had departed Nashville International Airport, Nashville, Tennessee, and was scheduled to fly to Baltimore-Washington International Airport, Baltimore, Maryland. 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 that point, the cabin altitude warning activated, and the captain disengaged the autopilot and began a descent. The altitude warning ceased as the airplane descended through approximately 9,000 feet. Cockpit voice recorder data and postincident interviews revealed that the flight and cabin crewmembers followed appropriate cockpit procedures following the rapid decompression and during the emergency descent and landing at CRW. Injuries to Persons No injuries occurred during the event. Damage to Aircraft A three-sided hole (flap) was located in skin assembly part number 65C35792-3 in the fuselage crown skin near the leading edge of the vertical stabilizer and measured about 17.4 inches longitudinally and between 11.5 and 8.6 inches circumferentially. Personnel Information The captain had accumulated 22,500 total flight hours, 19,300 hours of which were in the 737. He held an airline transport pilot (ATP) certificate and a class one medical certificate with a limitation/waiver for corrective lenses. The first officer had accumulated 10,100 total flight hours, 2,240 hours of which were in the 737. He held an ATP certificate and a class two medical certificate with no limitations/waivers. Aircraft Information 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. Tests and Research Skin assembly parts are made of an outer sheet of skin, which covers the entire assembly, and a waffle-pattern doubler sheet hot bonded to the inner surface of the part. Both pieces were 0.036-inch-thick, 2024–T3 clad aluminum sheets. Boeing indicated that the skin assembly was manufactured by forming and bonding two full sheets together, then selectively masking and chemically milling away pockets (bays) of the inner doubler sheet to create a waffle pattern. The bay immediately adjacent to the rupture is not chemically milled to provide for possible installation of an emergency locator transponder (ELT) antenna. Magnified inspections of the fracture surface of the skin assembly part revealed bright faceted surfaces indicativeof fatigue progress along the longitudinal section of the flap, which followed the chemically milled edge of the adjacent doubler. The circumferential crack regions displayed matte grey slant fracture surfaces and bulk deformation patterns indicative of overstress tearing away from the longitudinal portion of the crack. The longitudinal fatigue crack was 13.7 inches long from approximately BS 831 to BS 844. Highly magnified inspections of the longitudinal crack revealed continuous fatigue thumbnail cracks propagating outward (through-thickness) from multiple origins at the inner surface of the skin. The visual depth of the fatigue regions varied along the crack length. Near the middle of the longitudinal crack, the fatigue crack appeared to completely penetrate the skin thickness for a distance of approximately 3 inches. Scanning electron microscope examinations clearly showed microscopic features typical of fatigue progression, including areas of striations, in the longitudinal crack region. Additional Information The specific area of rupture and skin cracking (adjacent to the non-chemically milled skin to allow for a potential rear ELT antenna installation) associated with the SWA event was not subject to any inspection airworthiness directives (AD) or service bulletins (SB). However, Boeing finite element modeling suggests stress levels are higher in the skin at the edges of chemically milled steps adjacent to non-chemically milled bays due to the difference in stiffness. Following the SWA event, on September 3, 2009, Boeing issued 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 AD 2010-01-09, which mandated the inspection requirements in SB 737-53A1301. ## Aircraft - Registration: [N387SW](https://openairdocs.org/deregistered/N387SW-2022-07-09), registration cancelled 2022-07-09, S/N 26602, built 1994 (OpenAirDocs) - Reported make and model: BOEING 737 (3H4) - Registry model: [Boeing 737-3H4](https://openairdocs.org/model/boeing-737-3h4) (registry code 138447K) (OpenAirDocs) - Registry engine: [CFM International CFM56 series](https://openairdocs.org/engine/cfm-international-cfm56-series) (registry code 13802, turbo-fan) (OpenAirDocs) - Category: Airplane - Serial number: 26602 - Airframe hours: 50888 - Damage: Substantial damage - Flight: Part 121 - Operator: Southwest Airlines Co - Registered owner: US Bank NA Trustee - Airworthiness certificate: Standard, Transport - Last inspection: Continuous airworthiness, June 15, 2009 - Departed: BNA, Nashville, TN - Destination: BWI, Baltimore, MD - Flight plan: Unknown - Airport: CRW, Yeager Airport, Charleston, WV ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 53; injuries: none; commercial, private, airline transport; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 1, with waivers/limitations; last flight review June 14, 2009; seat: left; flight hours: 22,500 total, 19,300 in this make and model, 17,500 as pilot in command, 225 in the last 90 days, 75 in the last 30 days - Co-pilot; age 41; injuries: none; flight instructor, airline transport, commercial; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 2, without waivers/limitations; last flight review August 5, 2008; seat: right; flight hours: 10,100 total, 2,240 in this make and model, 6,300 as pilot in command, 167 in the last 90 days, 67 in the last 30 days ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 20090713024309A](https://openairdocs.org/incident/20090713024309A), Jul 13, 2009: Boeing 7373H4, Charleston, WV, Substantial damage. Charleston airport, WV (crw): southwest airlines flight 2294, a B737, enroute from nashville, TN (bna) to baltimore, MD (bwi) diverted and landed on runway 5… ## Docket (21 files) The files NTSB released with the investigation on August 18, 2010, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=74266. 15.6 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 473 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40333316&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - Pilot Statements (item 2, .PDF, 38 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40334614&FileExtension=.PDF&FileName=Pilot%20Statements-Master.PDF - Flight Attendant Statements (item 3, .PDF, 28 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40334615&FileExtension=.PDF&FileName=Flight%20Attendant%20Statements-Master.PDF - Flight Data Recorder 10 - Factual Report of Group Chairman (item 4, .PDF, 150 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40333539&FileExtension=.PDF&FileName=Flight%20Data%20Recorder%2010%20-%20Factual%20Report%20of%20Group%20Chairman-Master.PDF - Flight Data Recorder 10 - Attachment 1 FDR Tabular (item 5, .CSV, 762 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40333540&FileExtension=.csv&FileName=Flight%20Data%20Recorder%2010%20-%20Attachment%201%20FDR%20Tabular-Master.csv - Maintenance Records 11 - Factual Report of Group Chairman (item 6, .PDF, 68 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40325685&FileExtension=.PDF&FileName=Maintenance%20Records%2011%20-%20Factual%20Report%20of%20Group%20Chairman-Master.PDF - Maintenance Records 11 - Attachment 1 - Air Carrier Certificate (item 7, .PDF, 48 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40325452&FileExtension=.PDF&FileName=Maintenance%20Records%2011%20-%20Attachment%201%20-%20Air%20Carrier%20Certificate-Redacted.PDF - Maintenance Records 11 - Attachment 2 - Maintenance Informationa and Maintenance Check Schedule (item 8, .PDF, 138 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40325453&FileExtension=.PDF&FileName=Maintenance%20Records%2011%20-%20Attachment%202%20-%20Maintenance%20Informationa%20and%20Maintenance%20Check%20Schedule-Master.PDF - Maintenance Records 11 - Attachment 3 - Deferred and Open Items (item 9, .PDF, 582 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40325456&FileExtension=.PDF&FileName=Maintenance%20Records%2011%20-%20Attachment%203%20-%20Deferred%20and%20Open%20Items-Redacted.PDF - Maintenance Records 11 - Attachment 4 - Supplemental Type Certificate (item 10, .PDF, 142 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40325457&FileExtension=.PDF&FileName=Maintenance%20Records%2011%20-%20Attachment%204%20-%20Supplemental%20Type%20Certificate-Master.PDF - Maintenance Records 11 - Attachment 5 - Airworthiness Directive and Service Bulletin Listing (item 11, .PDF, 4.8 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40325459&FileExtension=.PDF&FileName=Maintenance%20Records%2011%20-%20Attachment%205%20-%20Airworthiness%20Directive%20and%20Service%20Bulletin%20Listing-Master.PDF - Maintenance Records 11 - Attachment 6 - Aircraft Flight Log (item 12, .PDF, 83 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40325460&FileExtension=.PDF&FileName=Maintenance%20Records%2011%20-%20Attachment%206%20-%20Aircraft%20Flight%20Log-Redacted.PDF - Maintenance Records 11 - Attachment 7 - Weight and Balance Summary (item 13, .PDF, 24 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40325461&FileExtension=.PDF&FileName=Maintenance%20Records%2011%20-%20Attachment%207%20-%20Weight%20and%20Balance%20Summary-Master.PDF - Maintenance Records 11 - Attachment 8 - Service Difficulty Reports and Mechanical Interruption Summary Reports (item 14, .PDF, 181 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40325462&FileExtension=.PDF&FileName=Maintenance%20Records%2011%20-%20Attachment%208%20-%20Service%20Difficulty%20Reports%20and%20Mechanical%20Interruption%20Summary%20Reports-Master.PDF - Maintenance Records 11 - Attachment 9 - Major Repairs and Alterations (item 15, .PDF, 468 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40325463&FileExtension=.PDF&FileName=Maintenance%20Records%2011%20-%20Attachment%209%20-%20Major%20Repairs%20and%20Alterations-Master.PDF - Maintenance Records 11 - Attachment 10 - Time Limit Components Listing (item 16, .PDF, 389 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40325464&FileExtension=.PDF&FileName=Maintenance%20Records%2011%20-%20Attachment%2010%20-%20Time%20Limit%20Components%20Listing-Master.PDF - Maintenance Records 11 - Attachment 11 - Crown Maintenance Program Requirements (item 17, .PDF, 1.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40325465&FileExtension=.PDF&FileName=Maintenance%20Records%2011%20-%20Attachment%2011%20-%20Crown%20Maintenance%20Program%20Requirements-Redacted.PDF - Maintenance Records 11 - Attachment 12 - N387SW Paint Information (item 18, .PDF, 1.9 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40325466&FileExtension=.PDF&FileName=Maintenance%20Records%2011%20-%20Attachment%2012%20-%20N387SW%20Paint%20Information-Redacted.PDF - Materials Laboratory 15 - Study 09-060S (item 19, .PDF, 393 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40327312&FileExtension=.PDF&FileName=Materials%20Laboratory%2015%20-%20Study%2009-060S-Master.PDF - Materials Laboratory 15 - Study 09-060S Appendix 1 (item 20, .PDF, 604 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40327323&FileExtension=.PDF&FileName=Materials%20Laboratory%2015%20-%20Study%2009-060S%20Appendix%201-Master.PDF - Materials Laboratory 15 - Factual Report 09-060 (item 21, .PDF, 3.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40318855&FileExtension=.PDF&FileName=Materials%20Laboratory%2015%20-%20Factual%20Report%2009-060-Master.PDF From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.