# NTSB DEN00IA032: Boeing 737-347, N305WA, Salt Lake City, UT, December 24, 1999 - Type: NTSB incident investigation - Classification: Incident · No injuries · Incident investigation · Final report - Date: December 24, 1999, 13:49 local (20:49 UTC) - Place: Salt Lake City, UT - Coordinates: 40.810379, -111.940048 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=40.8104&lon=-111.9400&mi=10 - Phase of flight: [Takeoff](https://openairdocs.org/ntsb-phases/300) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 135 uninjured - Status: Completed, report November 30, 2000 - Report: Approved by Office Director - NTSB case key (mKey): 48391 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=DEN00IA032 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/48391/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=48391 - Page: https://openairdocs.org/ntsb/DEN00IA032 ## Probable cause Improper assembly of the wheel during build up in the operator's maintenance facilities. ## Analysis During takeoff roll on a scheduled domestic passenger flight, the right main landing gear inboard wheel separated from the aircraft. The aircraft returned to the point of departure and landed without further incident. Examination of the landing gear revealed that the wrong wheel bearing had been installed when the wheel assembly was 'built up' at the operator's facility. ## Factual narrative On December 24, 1999, at 1349 mountain standard time, a Boeing 737-347, N305WA, operated by Delta Airlines as flight 1079 from Salt Lake City, Utah, to Detroit, Michigan, sustained minor damage when the landing gear right main inboard wheel assembly separated from the airplane during takeoff from Salt Lake City. There were no injuries to the 6 crew members and 127 passengers and the aircraft returned and landed at Salt Lake City, without incident, at 1630. The flight was operating under Title 14 CFR Part 121 as a scheduled domestic passenger flight and visual meteorological conditions prevailed. An IFR flight plan was filed. When the wheel separated from the aircraft it struck and damaged runway lighting. (See attached photographs.) Examination of the aircraft, following the event, revealed that a Boeing 757 main wheel bearing had been installed when the wheel was built up by Delta maintenance in Atlanta, Georgia. The difference between the two wheel bearings is the inner diameter of the bore. The correct bearing (part number 596) has a diameter of 3.375 inches and the incorrect bearing (part number 594) has a diameter of 3.750 inches. Boeing Commercial Airplane Group records search provided information that five cases of incorrect bearing installation have been reported to Boeing: Two cases in 1990, one in 1997, and two in 1999. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, takeoff - roll/run - landing gear,wheel - failure,partial (cause) - maintenance,installation - improper, company maintenance personnel (cause) - Miscellaneous/other, emergency descent/landing ## Aircraft - Registration: [N305WA](https://openairdocs.org/deregistered/N305WA-2007-05-04), registration cancelled 2007-05-04, S/N 23346, built 1985 (OpenAirDocs) - Reported make and model: Boeing 737-347 - Registry model: [Boeing 737-347](https://openairdocs.org/model/boeing-737-347) (registry code 138447U) (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: 23346 - Airframe hours: 36898 - Engines: GE CFM56-3 20000 lbs thrust turbo fan - Damage: Minor damage - Flight: Part 121 - Operator: Delta Airlines - Registered owner: State Street Bank And Trust - Airworthiness certificate: Standard, Transport - Last inspection: Continuous airworthiness, November 11, 1999 - Departed: SLC - Destination: DTW, DETROIT, MI - Flight plan: IFR - Airport: SLC, Salt Lake City Int'L, runway 34R, 12,004 × 150 ft, concrete ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 41; airline transport; airplane ratings: multi-engine land; instrument ratings: airplane; medical: class 1, valid medical--no waivers/lim.; seat: left; flight hours: 11,500 total, 1,850 in this make and model, 46 in the last 90 days ## Weather - Conditions: Visual (VMC), Day - Wind: 290° at 6 knots - Visibility: 6 statute miles - Lowest ceiling: none - Temperature: 36 °F, dew point 27 °F - Altimeter: 30.00 inHg - Observed at: SLC, 1 nm away ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Incident 19991224036029I](https://openairdocs.org/incident/19991224036029I), Dec 24, 1999: Boeing 737347, Salt Lake City, UT, Minor damage. (-23) Delta airlines flight 1079 departed Salt Lake City intl. At approx. 1425 hours LCL and reported loosing a main landing gear assy. The aircraft dumpted… ## Docket (6 files) The files NTSB released with the investigation on March 20, 2000, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=48391. 3.3 MB in all. - Supplement E (item 1, .PDF, 401 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40397375&FileExtension=.PDF&FileName=Supplement%20E-Redacted.PDF - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1/2 (item 2, .PDF, 551 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40397376&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1%2F2-Redacted.PDF - Maintenance Correspondence from Delta Airlines (item 3, .PDF, 1.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40397377&FileExtension=.PDF&FileName=Maintenance%20Correspondence%20from%20Delta%20Airlines-Redacted.PDF - Delta Airlines Maintenance Alert No. 12-28-99-18 (item 4, .PDF, 104 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40397378&FileExtension=.PDF&FileName=Delta%20Airlines%20Maintenance%20Alert%20No.%2012-28-99-18-Redacted.PDF - Correspondence from Boeing Airplane Group dated 1/6/00 (item 5, .PDF, 878 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40397379&FileExtension=.PDF&FileName=Correspondence%20from%20Boeing%20Airplane%20Group%20dated%201%2F6%2F00-Redacted.PDF - Correspondence from Boeing with Service Information Letter No. 6674 attached (item 6, .PDF, 201 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40397380&FileExtension=.PDF&FileName=Correspondence%20from%20Boeing%20with%20Service%20Information%20Letter%20No.%206674%20attached-Redacted.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.