# NTSB CEN22LA188: Beech B-99, N699CZ, Milwaukee, WI, April 30, 2022 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: April 30, 2022, 10:00 local (15:00 UTC) - Place: Milwaukee, WI - Coordinates: 42.946932, -87.897064 - Nearby events: https://openairdocs.org/map.md?lat=42.9469&lon=-87.8971&mi=10 - Phase of flight: [Taxi](https://openairdocs.org/ntsb-phases/250) (OpenAirDocs' grouping) - Defining event: [Taxi: Landing gear collapse](https://openairdocs.org/ntsb-events/094) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Central Region - Parties: FAA MKE FSDO - NTSB case key (mKey): 105033 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN22LA188 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/105033/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=105033 - Page: https://openairdocs.org/ntsb/CEN22LA188 ## Probable cause A right main landing gear collapse due to fatigue failure of the landing gear drag leg support fitting. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Landing gear system: main landing gear](https://openairdocs.org/ntsb-findings/01023210): Aircraft › Aircraft systems · Fatigue/wear/corrosion (probable cause); cases with it: [Beech B-99, 1 case](https://openairdocs.org/ntsb-findings/01023210/cases.md?model=1154004), [All aircraft, 241 cases](https://openairdocs.org/ntsb-findings/01023210/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Taxi: Landing gear collapse](https://openairdocs.org/ntsb-events/094) (defining event); cases with it: [Beech B-99, 1 case](https://openairdocs.org/ntsb-events/094/sequence.md?model=1154004), [All aircraft, 1,787 cases](https://openairdocs.org/ntsb-events/094/sequence.md) ## Analysis The pilot reported no difficulties during the flight or landing. While taxing the airplane after landing, the green right landing gear position indicator light extinguished, and the red gear handle light illuminated. The pilot glanced over to the circuit breaker panel and noted that the landing gear control circuit breaker had tripped. After parking the airplane for refueling, he notified his company maintenance control group about the issue and was advised to not reposition the airplane after refueling. The pilot waited about 20 minutes for weather to clear before exiting the airplane. As the pilot prepared to exit, the right main landing gear collapsed and the airplane’s right wing impacted the ground, resulting in substantial damage. Metallurgical examination of the separated fracture surface on the right landing gear drag leg support fitting revealed an area of fatigue in a machined radius adjacent to the center lug of the drag leg support. The remainder of the fracture exhibited features consistent with overload failure. An additional crack was found in the machined radius on the opposite side of the center lug. This portion of the part had not completely separated. Exposure of the crack revealed the existence of a fatigue crack in about the same area as the first crack, with overload signatures outside of the fatigue area. The airplane maintenance manual indicated that the subject part was to be cleaned and visually inspected at least every 7,500 cycles or every 5 years, whichever occurred first. Maintenance records indicated that the part had accumulated 762 cycles since the most recent inspection 23 months before the accident. After the accident, the operator examined the drag leg support fittings on their fleet of 9 other airplanes of the same model. Of the 18 fittings examined, 14 were found to be cracked. Of the 14 cracked fittings, 11 could only be detected using dye penetrant inspection, and could not be detected solely by visual inspection. ## Factual narrative On April 30, 2022, about 1000 central daylight time, a Beech B-99 airplane, N699CZ, was substantially damaged when it was involved in an accident at General Mitchell International Airport (MKE), Milwaukee, Wisconsin. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 135 cargo flight. The flight originated from Baraboo/Wisconsin Dells Regional Airport (DLL), Baraboo, Wisconsin, with MKE as the intended destination. As the airplane approached MKE, the pilot was cleared by air traffic control (ATC) for the visual approach for runway 19R. He noted that the landing was “smooth given the weather conditions,” and he used normal braking to exit the runway. Upon entering the ramp area, the green right landing gear position light extinguished, and the red gear handle light illuminated. The pilot glanced over to the circuit breaker panel and noticed that the “Landing Gear Control” circuit breaker had tripped. After parking the airplane for refueling, he notified his company maintenance control group about the issue and was advised to not reposition the airplane after refueling. The pilot waited about 20 minutes for weather to clear before exiting the airplane. As he prepared to exit the airplane, the right main landing gear collapsed and the airplane’s right wing impacted the ground, resulting in substantial damage to the right wing. After the accident, it was discovered that the right landing gear drag leg support fitting, part number 50-120201-1, had broken. Further examination by the operator determined that the same part on the left landing gear was also fractured. Metallurgical examination of the separated fracture surface on the right landing gear drag leg support fitting revealed an area of fatigue in a machined radius adjacent to the center lug of the drag leg support. The remainder of the fracture exhibited features consistent with overload failure. An additional crack was found in the machined radius on the opposite side of the center lug. This portion of the part had not completely separated. Exposure of the crack revealed the existence of a fatigue crack in about the same area as the first crack, with overload signatures outside of the fatigue area. Maintenance manual excerpts for the airplane indicated that the subject part was to be cleaned and visually inspected at least every 7,500 cycles or every 5 years, whichever occurred first. If visual examination revealed a crack, it was to be verified by dye penetrant inspection. Any cracks found required replacement of the part. Maintenance records indicated that the part had accumulated 762 cycles since the last inspection 23 months prior. The operator reported that the accident airplane was maintained using an Approved Aircraft Inspection Program (AAIP) and had accumulated 35,012.9 total flight hours and 43,054 total cycles at the time of the accident. The most recent inspection of the drag leg support fitting was performed on May 11, 2020. Theoperator examined all the drag leg support fittings on their fleet of nine Beech B-99 airplanes, not including the accident airplane. Of the 18 drag leg support fittings examined, 14 were found to be cracked. Of the 14 cracked fittings, 11 required dye penetrant inspection to be detected; the cracks could not be detected solely by visual inspection. The operator had a previous accident (NTSB report number ERA21LA021), on October 14, 2020, involving another Beech B-99 airplane. In that accident, the right main landing gear collapsed as the airplane was taxied from the runway after landing. The drag leg support fitting was also found to have fatigue cracking in the same area of the fitting. ## Aircraft - Registration: [N699CZ](https://openairdocs.org/aircraft/N699CZ), registered now, S/N U-10, built 1968 (OpenAirDocs) - Reported make and model: BEECH B-99 - Registry model: [Beech B-99](https://openairdocs.org/model/beech-b-99) (registry code 1154004) (OpenAirDocs) - Category: Airplane - Serial number: U-10 - Year built: 1968 - Airframe hours: 35012.9 - Engines: Pratt & Whitney PT6A 550 horsepower turbo prop; Pratt & Whitney PT6A 550 horsepower turbo prop - Damage: Substantial damage - Flight: Business, Part 135 - Operator: Freight Runners - Registered owner: N699cz LLC - Airworthiness certificate: Standard, Normal - Departed: DLL, Baraboo, WI - Destination: Same as departure - Airport: MKE, General Mitchell International Airport - Equipment: ADS-B ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 29; injuries: none; airline transport; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 1, without waivers/limitations; last flight review February 28, 2022; seat: left; restraint: 4-point; flight hours: 2,784 total, 320 in this make and model, 1,675 as pilot in command, 220 in the last 90 days, 53 in the last 30 days, 0 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 130° at 15 knots, gusting 23 - Visibility: 10 statute miles - Lowest ceiling: 4,200 ft broken - Temperature: 46 °F, dew point 37 °F - Altimeter: 29.87 inHg - Observed at: MKE - METAR: ETAR KMKE 301452Z 13015G23KT 10SM -RA BKN042 BKN080 OVC090 08/03 A2987 RMK AO2 SLP117 P0001 60001 T00830028 58025= ## 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 20220430002579A](https://openairdocs.org/incident/20220430002579A), Apr 30, 2022: Beech B-99, Milwaukee, WI, Substantial damage. On April 30, 2022 at approximately 0937 N699CZ a Beechcraft 99 [privacy data omitted] experienced a right main landing gear collapse after taxiing to ramp and… ## Docket (7 files) The files NTSB released with the investigation on March 13, 2024, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=105033. 12.8 MB in all. - Materials laboratory factual report 22-100 (item 1, PDF, 21 pages, 18 photos, 9.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15748428&FileExtension=pdf&FileName=Materials%20Laboratory%20Factual%20Report%2022-100-Rel.pdf - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 2, PDF, 9 pages, 807 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16623674&FileExtension=pdf&FileName=6120-2_Redacted-Rel.pdf - Fleet bracket inspection by operator (item 3, PDF, 1 page, 207 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16623773&FileExtension=pdf&FileName=Freight%20Runners%20B99%20Fleet%20Bracket%20insp.-Rel.pdf - Maintenance manual excerpt (item 4, PDF, 1 page, 54 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16623932&FileExtension=pdf&FileName=99%20Maintenance%20Manual%2032-10-00%20(1)-Rel.pdf - Release of aircraft wreckage, NTSB form 6120.15 (item 5, PDF, 1 page, 573 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16625066&FileExtension=pdf&FileName=N699CZ%20NTSB%20Release_Redacted-Rel.pdf - Accident photographs (item 6, PDF, 3 pages, 2 photos, 467 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16739340&FileExtension=pdf&FileName=Photos-Rel.pdf - Maintenance information (item 7, PDF, 10 pages, 1.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16741327&FileExtension=pdf&FileName=Maint_Redacted-Rel.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.