# NTSB WPR10LA173: Williams Yakovlev YAK 3UPW, N153U, Half Moon Bay, CA, March 22, 2010 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: March 22, 2010, 14:30 local (21:30 UTC) - Place: Half Moon Bay, CA - Coordinates: 37.51361, -122.501113 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=37.5136&lon=-122.5011&mi=10 - Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping) - Defining event: [Landing-landing roll: Landing gear collapse](https://openairdocs.org/ntsb-events/094) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report August 12, 2010 - Report: Approved by Office Director - NTSB office: Western Pacific Region - Parties: Federal Aviation Administration - NTSB case key (mKey): 75562 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR10LA173 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/75562/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=75562 - Page: https://openairdocs.org/ntsb/WPR10LA173 ## Probable cause The failure of left main landing gear actuator to lock in the down position due to low down-lock pressure as a result of a contaminated down-lock track and corroded down-lock balls. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Landing gear system: landing gear actuator](https://openairdocs.org/ntsb-findings/01023233): Aircraft › Aircraft systems · Malfunction (probable cause); cases with it: [All aircraft, 54 cases](https://openairdocs.org/ntsb-findings/01023233/cases.md) - [Landing gear system: landing gear actuator](https://openairdocs.org/ntsb-findings/01023233): Aircraft › Aircraft systems · Fatigue/wear/corrosion (probable cause); cases with it: [All aircraft, 54 cases](https://openairdocs.org/ntsb-findings/01023233/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Landing-landing roll: Landing gear collapse](https://openairdocs.org/ntsb-events/094) (defining event); cases with it: [All aircraft, 1,787 cases](https://openairdocs.org/ntsb-events/094/sequence.md) ## Analysis Prior to landing the pilot observed 3 green lights indicating that the landing gear was down and locked. During the landing roll the left main landing gear collapsed, which resulted in substantial damage to the left wing and aileron. A Federal Aviation Administration inspector reported that a postaccident examination of the left main landing gear's pneumatic actuator revealed that the actuator's down-lock ball track was contaminated with dirt and that the steel down-lock balls were corroded. The combination of dirt in the actuator's down-lock track, the corroded down-lock balls, and the low down-lock pressure likely caused the gear to collapse. ## Factual narrative On March 22, 2010, about 1430 Pacific daylight time, a Willams Yakovlev 3UPW, N153U, sustained substantial damage following the collapse of the left main landing gear during landing roll at the Half Moon Bay Airport (HAF), Half Moon Bay, California. The private pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed for the local flight, which was being operated in accordance with 14 Code of Federal Regulations (CFR) Part 91, and a flight plan was not filed. The airplane departed HAF about 1420. In a statement submitted to the Safety Board investigator-in-charge (IIC), the pilot reported that after taking off and returning to the airport traffic pattern, he extended the landing gear. The pilot stated, “Everything was in the green. Three lights for the gear and mechanical indicators showing the gear down. I made a normal landing, and when the full weight of the plane was on the mains the left [landing] gear collapsed.” The pilot added that the airplane went off the left side of the runway and came to rest on a heading of 120 degrees after landing on runway 30. The pilot reported that the outer one-third of the left wing, the left aileron and the left flap were bent. The pilot further reported that the propeller blades were bent, the tail wheel had broken off, and the left landing gear doors were bent. The pilot revealed that the airplane was manufactured in 1995 and not assembled until 2005, when he purchased it. On April 27, 2010, under the supervision of a Federal Aviation Administration (FAA) airworthiness inspector, a FAA certified airframe and powerplant mechanic conducted a teardown examination of the airplane’s left main landing gear pneumatic actuator. After removing the actuator and applying shock air to the component, the mechanic reported that operation of the actuator appeared to be normal, with no internal or external leaks noted. The mechanic stated that downline air pressure normally forces the down lock balls into the down lock track to lock the actuator in the down position. When the actuator was disassembled, the mechanic reported that he observed that the actuator’s down lock ball track was contaminated with dirt and that the steel down lock balls were corroded. The mechanic stated, "I believe a combination of dirt in the down lock track, corroded down lock balls, and low down lock pressure caused the gear to collapse.” The FAA inspector reported that he concurred with the mechanic’s statement. ## Aircraft - Registration: N153U (not matched to a registry record) - Reported make and model: Williams Yakovlev YAK 3UPW - Category: Airplane - Serial number: 005 - Airframe hours: 21 - Engines: Pratt & Whitney R-1830 1400 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Operator: James A Williams - Registered owner: Yak Aviation LLC - Airworthiness certificate: Special, Experimental (Special) - Last inspection: Annual, March 1, 2010, 21 hours before - Departed: HAF, Half Moon Bay, CA - Destination: HAF, Half Moon Bay, CA - Airport: HAF, Half Moon Bay, runway 30, 5,000 × 150 ft, concrete ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 74; injuries: none; private; airplane ratings: single-engine land; medical: class 3, with waivers/limitations; last flight review July 2, 2008; seat: front; flight hours: 3,746 total, 21 in this make and model, 3,746 as pilot in command ## Weather - Conditions: Visual (VMC), Day - Wind: 330° at 15 knots, gusting 21 - Visibility: 6 statute miles - Lowest ceiling: none - Temperature: 57 °F, dew point 48 °F - Altimeter: 30.06 inHg - Observed at: HAF ## Docket (3 files) The files NTSB released with the investigation on June 6, 2010, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=75562. 765 KB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 713 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40329848&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - Weather Report (item 2, .PDF, 40 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40329849&FileExtension=.PDF&FileName=Weather%20Report-Master.PDF - FAA Inspector's Report of Actuator Examination (item 3, .PDF, 13 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40329850&FileExtension=.PDF&FileName=FAA%20Inspector%27s%20Report%20of%20Actuator%20Examination-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.