# NTSB ENG12IA001: Boeing 757-251, N553NW, Atlanta, GA, October 10, 2011 - Type: NTSB incident investigation - Classification: Incident · No injuries · Incident investigation · Final report - Date: October 10, 2011, 15:03 local (19:03 UTC) - Place: Atlanta, GA - Coordinates: 33.763332, -84.401664 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=33.7633&lon=-84.4017&mi=10 - Phase of flight: [Takeoff](https://openairdocs.org/ntsb-phases/300) (OpenAirDocs' grouping) - Defining event: [Takeoff-rejected takeoff: Uncontained engine failure](https://openairdocs.org/ntsb-events/343) - Highest injury: No injuries - Injuries: 182 uninjured - Status: Completed, report October 23, 2014 - Report: Approved by Office Director - NTSB office: Aviation Engineering Division - Parties: Federal Aviation Administration - ADs cited in the narratives: [AD 2014-05-32](https://openairdocs.org/ad/2014-05-32) (OpenAirDocs) - NTSB case key (mKey): 82022 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ENG12IA001 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/82022/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=82022 - Page: https://openairdocs.org/ntsb/ENG12IA001 ## Probable cause the return to service of overhauled airplane engine parts with undetected fatigue cracks, resulting in complete loss of engine power and uncontained engine failure. A contributing factor was the inadequate diffuser and HPT case inspection procedure. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Engine (turbine/turboprop): combustion section](https://openairdocs.org/ntsb-findings/01057240): Aircraft › Aircraft power plant · Incorrect service/maintenance (probable cause); cases with it: [Boeing 757-251, 1 case](https://openairdocs.org/ntsb-findings/01057240/cases.md?model=1384970), [All aircraft, 9 cases](https://openairdocs.org/ntsb-findings/01057240/cases.md) - [Engine (turbine/turboprop): combustion section](https://openairdocs.org/ntsb-findings/01057240): Aircraft › Aircraft power plant · Fatigue/wear/corrosion; cases with it: [Boeing 757-251, 1 case](https://openairdocs.org/ntsb-findings/01057240/cases.md?model=1384970), [All aircraft, 9 cases](https://openairdocs.org/ntsb-findings/01057240/cases.md) - [Engine (turbine/turboprop): combustion section](https://openairdocs.org/ntsb-findings/01057240): Aircraft › Aircraft power plant · Failure; cases with it: [Boeing 757-251, 1 case](https://openairdocs.org/ntsb-findings/01057240/cases.md?model=1384970), [All aircraft, 9 cases](https://openairdocs.org/ntsb-findings/01057240/cases.md) - [Engine (turbine/turboprop): combustion section](https://openairdocs.org/ntsb-findings/01057240): Aircraft › Aircraft power plant · Inadequate inspection (probable cause); cases with it: [Boeing 757-251, 1 case](https://openairdocs.org/ntsb-findings/01057240/cases.md?model=1384970), [All aircraft, 9 cases](https://openairdocs.org/ntsb-findings/01057240/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Takeoff-rejected takeoff: Uncontained engine failure](https://openairdocs.org/ntsb-events/343) (defining event); cases with it: [Boeing 757-251, 1 case](https://openairdocs.org/ntsb-events/343/sequence.md?model=1384970), [All aircraft, 47 cases](https://openairdocs.org/ntsb-events/343/sequence.md) - [Takeoff-rejected takeoff: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342); cases with it: [Boeing 757-251, 1 case](https://openairdocs.org/ntsb-events/342/sequence.md?model=1384970), [All aircraft, 1,858 cases](https://openairdocs.org/ntsb-events/342/sequence.md) ## Analysis The diffuser case of a Pratt & Whitney PW2037(M) engine installed on a B757-200 airplane ruptured during takeoff roll at Hartsfield-Jackson Atlanta International Airport, Atlanta, Georgia (ATL). The force of the case rupture caused the hinge-mounted core cowl halves to distort and strike the leading edge and underside of the airplane's left wing, resulting in minor airplane damage. Metallurgical investigation and review of the engine's maintenance records determined that cracks in the engine's diffuser case rear flange (M-flange) and cracks in the HPT case forward flange (M-flange) were not detected when the cases underwent fluorescent penetrant inspection (FPI) during the engine's last shop visit, 3,479 cycles before the event. The undetected cracks continued to propagate, leading to the in-service diffuser case rupture. The reason for the ineffective inspection was not determined, but was narrowed to chronological- and operator-based scenarios. A suspect population of 50 engines was identified that included sub-populations for both possibilities. The FAA published airworthiness directive (AD) 2014-05-32, requiring the M-flanges of PW2037, PW2037D, PW2037M, PW2040, PW2040D, PW2043, PW2143, PW2240, PW2337, PW2643, and F117-PW-100 engines in the identified suspect population to undergo eddy current inspection within 100 flight cycles or 30 days. No additional cracks were found. As a result of the investigation, the FAA published airworthiness directive (AD) 2014-05-32, which requires the M-flanges of PW2000 engines with certain diffuser and HPT cases installed to undergo eddy current inspection within 100 flight cycles or 30 days. AD 2014-05-32 also requires that high-sensitivity FPI penetrant be used when accomplishing FPI of the PW2037, PW2037D, PW2037M, PW2040, PW2040D, PW2043, PW2143, PW2240, PW2337, PW2643, and F117-PW-100 diffuser case M-flange and the HPT case M-flange. In addition, AD 2014-05-32 makes the performance of diffuser and HPT case M-flange high-sensitivity FPI at every piece part opportunity an airworthiness limitation for PW2037, PW2037D, PW2037M, PW2040, PW2040D, PW2043, PW2146, PW2240, PW2337, PW2643, and F117-PW-100 engines. ## Factual narrative HISTORY OF FLIGHT On October 10, 2011 at about 3:04 eastern daylight time, a Delta Air Lines (DAL) Boeing 757-200, N553NW, powered by two Pratt & Whitney PW2037(M) turbofan engines, experienced a left engine failure during takeoff roll at Hartsfield-Jackson Atlanta International Airport, Atlanta, Georgia (ATL). The flight crew reported that, at about 60 kias, they heard a loud bang and noted left engine fire indications. The captain aborted the takeoff and shut down the engine, and the airplane was taxied back to the gate without further incident. The airplane was operating on an instrument flight rules flight plan as domestic passenger flight 2210 in accordance with the provisions of 14 Code of Federal Regulations (CFR) Part 121, from ATL to Dallas Ft. Worth International Airport, Ft. Worth, Texas. No injuries were reported, and there was minor damage to the airplane. Post-incident inspection of the airplane found that the left engine diffuser case had ruptured. DAMAGE TO THE AIRCRAFT The leading edge and underside of the airplane's left wing had numerous dents and small impact marks. Both halves of the left engine core cowl, which is hinge-mounted on the pylon, were severely distorted. The core cowl halves could be rotated beyond their normal range of travel until they contacted the left wing, and the location of the wing damage was consistent with having been struck by the core cowl halves during the rupture event. DIFFUSER CASE RUPTURE The engine diffuser case, high pressure turbine (HPT) case, and nozzle guide vane (NGV) support joint, referred to as the "M-flange," were fractured at a bolt hole located at 12 o'clock (BH1). A longitudinal fracture extended from BH1 about 15 inches forward into the diffuser case and about 2.5 inches aft into the HPT case. There was a 270° circumferential fracture in the diffuser case about 15 inches forward of the M-flange, and a 120° circumferential fracture in the HPT case about 2.5 inches aft of the M-flange; an approximately 15-inch-wide section of the diffuser case, along with fractured segments of the HPT case and NGV support attached at the M-flange, had unwrapped from the right side of the engine. The engine was disassembled and the diffuser case, NGV support, and HPT case were shipped to the NTSB materials lab for further investigation. TESTS AND RESEARCH Materials investigation Metallurgical examination of the diffuser case, NGV support, and HPT case fracture surfaces revealed that low cycle fatigue cracks had initiated in all three components at the M-flange bolt hole and propagated across the flange surface inboard of the bolt hole (inner strap) and the flange surface outboard of the bolt hole (outer strap). Scanning electron microscopy found discernible fatigue striation marks on the diffuser case and the HPT case fracture surfaces. Fatigue striations are marks left on a fracture surface as a crack advances with each stress cycle, and the number of engine cycles required to produce a fatiguecrack can sometimes be estimated by counting the striations and analyzing the striation counts, along with other data. Analysis of these data determined that the first fatigue crack initiated in the HPT case, followed by crack initiation in the diffuser case. Cracks had propagated through the HPT case M-flange outer and inner straps over approximately 7,305 and 7,384 cycles, respectively, and the cracks in the diffuser case M-flange propagated through the outer and inner straps over approximately 2,471 and 5,159 cycles, respectively. Continued airworthiness of turbine cases The continued airworthiness of PW2000 diffuser and HPT cases is ensured by periodic fluorescent penetrant inspection (FPI). FPI is a surface crack detection method that uses a penetrating fluid with a fluorescent suspension that enters crack separations by capillary action. A black light is used to visually detect cracks containing the fluid. Diffuser and HPT cases undergo FPI when completely disassembled in accordance with the manufacturer recommendation. No cracks are permitted. According to Delta Air Lines maintenance records, the diffuser case and the HPT case were last exposed for inspection during overhaul at Pratt & Whitney's Cheshire Engine Center (P&W CEC) in August, 2008, 3,479 cycles before the failure. A review of the P&W CEC shop records found that both the diffuser case and the HPT case underwent FPI during this shop visit, and were returned to service with no cracks found. Crack growth study findings The crack growth study found that an approximate 0.46-inch crack was present in the HPT case M-flange inner strap and case wall, an approximate 0.26-inch crack was present in the diffuser case M-flange and case wall, and that both diffuser and HPT case M-flange outer straps were cracked through when the cases were overhaul inspected at P&W CEC. The crack growth study also showed that the first fatigue crack initiated in the HPT case, followed by crack initiation in the diffuser case. The P&W CEC repair station was closed in August 2011. The reason for the ineffective inspection was not determined, but was narrowed to chronological and operator based scenarios. A suspect population of 50 engines was identified that included sub-populations for both possibilities. The FAA published airworthiness directive (AD) 2014-05-32, requiring the M-flanges of PW2037, PW2037D, PW2037M, PW2040, PW2040D, PW2043, PW2143, PW2240, PW2337, PW2643, and F117-PW-100 engines in the identified suspect population to undergo eddy current inspection within 100 flight cycles or 30 days. No additional cracks were found. ADDITIONAL INFORMATION Corrective actions AD 2014-05-32 also requires that, effective May 5, 2014, high-sensitivity FPI penetrant be used when accomplishing FPI of the PW2037, PW2037D, PW2037M, PW2040, PW2040D, PW2043, PW2143, PW2240, PW2337, PW2643, and F117-PW-100 diffuser case aft flange (M-flange) and HPT case forward flange (M-flange). In addition, AD 2014-05-32 makes theperformance of diffuser and HPT case M-flange high-sensitivity FPI at every piece part opportunity an airworthiness limitation for PW2037, PW2037D, PW2037M, PW2040, PW2040D, PW2043, PW2146, PW2240, PW2337, PW2643, and F117-PW-100 engines. ## Aircraft - Registration: [N553NW](https://openairdocs.org/aircraft/N553NW), registered now, S/N 26500, built 2001 (OpenAirDocs) - Reported make and model: BOEING 757-251 - Registry model: [Boeing 757-251](https://openairdocs.org/model/boeing-757-251) (registry code 1384970) (OpenAirDocs) - Registry engine: [Pratt & Whitney PW2037](https://openairdocs.org/engine/pratt-whitney-pw2037) (registry code 52117, turbo-fan) (OpenAirDocs) - Category: Airplane - Serial number: 26500 - Engines: P & W PW2037 37530 lbs thrust turbo jet; P & W PW2037 37530 lbs thrust turbo jet - Damage: Minor damage - Fire: On-Ground - Flight: Part 121 - Operator: Delta Air Lines Inc - Registered owner: Delta Air Lines Inc - Airworthiness certificate: Standard, Transport - Departed: ATL, Atlanta, GA - Destination: DFW, Dallas, TX - Flight plan: Unknown - Airport: ATL, Hartsfield - Jackson Atlanta I ## Weather - Conditions: Visual (VMC), Day ## Docket (10 files) The files NTSB released with the investigation on April 2, 2013, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=82022. 70.5 MB in all. - Powerplants 8 - Factual Report of Group Chairman with 21 embedded photographs (item 1, .PDF, 21 photos, 3.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40389957&FileExtension=.PDF&FileName=Powerplants%208%20-%20Factual%20Report%20of%20Group%20Chairman%20with%2021%20embedded%20photographs-Master.PDF - Flight Data Recorder 10 - Specialist's Factual Report (item 2, .PDF, 460 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40373262&FileExtension=.PDF&FileName=Flight%20Data%20Recorder%2010%20-%20Specialist%27s%20Factual%20Report-Master.PDF - Flight Data Recorder 10 - Attachment 1 (FDR tabular data for event) (item 3, .CSV, 1.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40373250&FileExtension=.csv&FileName=Flight%20Data%20Recorder%2010%20-%20Attachment%201%20(FDR%20tabular%20data%20for%20event)-Master.csv - Flight Data Recorder 10 - Attachment 2 (FDR tabular data for first previous flight) (item 4, .CSV, 8.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40373251&FileExtension=.csv&FileName=Flight%20Data%20Recorder%2010%20-%20Attachment%202%20(FDR%20tabular%20data%20for%20first%20previous%20flight)-Master.csv - Flight Data Recorder 10 - Attachment 3 (FDR tabular data for second previous flight) (item 5, .CSV, 9.9 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40373252&FileExtension=.csv&FileName=Flight%20Data%20Recorder%2010%20-%20Attachment%203%20(FDR%20tabular%20data%20for%20second%20previous%20flight)-Master.csv - Materials Laboratory 15 - Factual Report 12-028 (with 63 embedded images) (item 6, .PDF, 10.6 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40381985&FileExtension=.PDF&FileName=Materials%20Laboratory%2015%20-%20Factual%20Report%2012-028%20(with%2063%20embedded%20images)-Master.PDF - Materials Laboratory 15 - Factual Report 12-028 - Appendices A - D (with 69 embedded images) (item 7, .PDF, 14.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40381986&FileExtension=.PDF&FileName=Materials%20Laboratory%2015%20-%20Factual%20Report%2012-028%20-%20Appendices%20A%20-%20D%20(with%2069%20embedded%20images)-Master.PDF - Materials Laboratory 15 - Factual Report 12-028 - Appendices E - G (with 50 embedded images) (item 8, .PDF, 20.0 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40381987&FileExtension=.PDF&FileName=Materials%20Laboratory%2015%20-%20Factual%20Report%2012-028%20-%20Appendices%20E%20-%20G%20(with%2050%20embedded%20images)-Master.PDF - Materials Laboratory 15 - Study Report 12-028S (with 2 embedded images) (item 9, .PDF, 1.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40381988&FileExtension=.PDF&FileName=Materials%20Laboratory%2015%20-%20Study%20Report%2012-028S%20(with%202%20embedded%20images)-Master.PDF - Materials Laboratory 15 - Attachment 1 - SEM Image of Fracture Surface (item 10, .PDF, 180 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40389854&FileExtension=.PDF&FileName=Materials%20Laboratory%2015%20-%20Attachment%201%20-%20SEM%20Image%20of%20Fracture%20Surface-Master.PDF From the NTSB's public API. 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