# NTSB WPR11LA320: Schweizer G-164B, N7503L, Yuba City, CA, July 9, 2011 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: July 9, 2011, 14:30 local (21:30 UTC) - Place: Yuba City, CA - Coordinates: 39.068332, -121.735275 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=39.0683&lon=-121.7353&mi=10 - Phase of flight: [Initial climb](https://openairdocs.org/ntsb-phases/350) (OpenAirDocs' grouping) - Defining event: [Initial climb: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report August 14, 2014 - Report: Approved by Office Director - NTSB office: Western Pacific Region - Parties: SAC FSDO - NTSB case key (mKey): 81066 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR11LA320 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/81066/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=81066 - Page: https://openairdocs.org/ntsb/WPR11LA320 ## Probable cause High-cycle fatigue on the 1st-stage compressor blade retaining ring, which resulted in the ring’s fracture and a subsequent loss of engine power. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Engine (turbine/turboprop): compressor section](https://openairdocs.org/ntsb-findings/01057230): Aircraft › Aircraft power plant · Fatigue/wear/corrosion (probable cause); cases with it: [Schweizer G-164B, 1 case](https://openairdocs.org/ntsb-findings/01057230/cases.md?model=8059055), [All aircraft, 53 cases](https://openairdocs.org/ntsb-findings/01057230/cases.md) - [Terrain: rough terrain](https://openairdocs.org/ntsb-findings/03021015): Environmental issues › Physical environment · Effect on equipment; cases with it: [Schweizer G-164B, 2 cases](https://openairdocs.org/ntsb-findings/03021015/cases.md?model=8059055), [All aircraft, 442 cases](https://openairdocs.org/ntsb-findings/03021015/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Initial climb: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) (defining event); cases with it: [Schweizer G-164B, 6 cases](https://openairdocs.org/ntsb-events/341/sequence.md?model=8059055), [All aircraft, 3,820 cases](https://openairdocs.org/ntsb-events/341/sequence.md) - [Landing-landing roll: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Schweizer G-164B, 4 cases](https://openairdocs.org/ntsb-events/440/sequence.md?model=8059055), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md) ## Analysis The pilot reported that, during the initial climb, he heard a "loud pop" and observed fire coming from both exhaust stacks before the engine lost power. He subsequently made an off-airport landing to an adjacent road. During the landing, the airplane slid into a ditch, the landing gear sheared off, and the airplane nosed over. A postaccident engine examination revealed that the blade retaining ring of the 1st-stage compressor blades had fractured into several pieces; about 30 percent of the ring was not recovered. A metallurgical examination of the recovered sections of the retaining ring revealed that all but two of the fractures were due to ductile overload. An examination of the nonoverload fractures revealed fatigue originating from the rivet hole areas, which was indicative of high-cycle fatigue. The power section had been overhauled 747 hours before the accident. According to the overhaul manual current at the time of the overhaul, the blade retaining ring was an on-condition inspection item and not required to be replaced at overhaul. The fatigue fracture of the 1st-stage compressor blade retaining ring likely affected the engine's ability to produce power. ## Factual narrative PWC updated section 72-30-05, page 107, paragraph B(4) of the engine Overhaul Manual on August 8, 2013, to indicate that the blade retaining ring should be discarded at disassembly. The airplane was a Schweizer G164B Ag Cat, serial number 826B. The operator reported that the airplane had a total airframe time of 10,282 hours at the last annual inspection on April 19, 2011. The engine was a Pratt & Whitney Canada (PWC) PT6A-34, serial number PCE 56022. Total time recorded on the engine at the last 100-hour annual inspection was 8,878 hours. The engine had 747.7 hours since overhaul on March 5, 2009. On July 9, 2011, about 1430 Pacific daylight time, a Schweizer G-164B, N7503L, encountered a ditch during an off airport forced landing following a loss of engine power near Yuba City, California. Onstott Dusters, Inc., was operating the airplane under the provisions of 14 Code of Federal Regulations (CFR) Part 137. The commercial pilot was not injured; the airplane sustained substantial damage from impact forces. The local aerial application flight was departing from a private dirt strip. Visual meteorological conditions prevailed, and no flight plan had been filed. The pilot stated that the airplane reached about 35 feet above ground level after takeoff when he heard a loud pop. He observed fire coming from both exhaust stacks, and the engine lost power. He landed on an adjacent road, but the airplane slid into a ditch alongside it. The landing gear sheared off, and the airplane nosed over. PWC examined the engine under the supervision of a Federal Aviation Administration (FAA) inspector at the PWC Service Investigation Facilities in Bridgeport, West Virginia on January 11, 2012, and the PWC materials laboratory completed a follow up metallurgical exam. A report of the findings is part of the public docket for this accident. Pertinent excerpts follow. No debris was observed on the magnetic poles of the reduction gearbox chip detector. The oil filter was clean, and the residual oil in the filter and housing was clean. The fuel filter was clean, and residual fuel in the filter and housing was clean. Compressor Section The 1st stage compressor blades had damage on the leading and trailing edge of the airfoils. The blade retaining ring had fractured into several pieces; approximately 30 percent of the ring was not recovered. The rear hub (1st stage rotor) was in good condition; four of the six required blade retaining ring's retention rivets were in place, but the flared end had fractured against the hub. The PWC metallurgist's examination of the recovered sections of the retaining ring revealed that all but two of the fractures were due to ductile overload. A Scanning Electron Microscope (SEM) examination of one of the non-overload fractures exhibited fatigue that originated from the rivet hole area. The fatigue cracks were indicative of high cycle fatigue (HCF) from the rivet hole. The area on the opposite side of the rivet hole fractured in shear. ASEM examination of the second fatigue crack location also indicated HCF. No material anomalies were found at the fatigue initiation site area, and the chemical composition of the ring met manufacturing drawing requirements. Per the current Overhaul Manual (P/N 3021243 rev 31, dated December 15, 2006) at the time of the overhaul, the blade retaining ring was an on-condition at inspection item, and not required to be replaced at overhaul. The 2nd and 3rd stage compressor blades exhibited leading edge damage, the tips were battered, and there was trailing edge deformation. The compressor disk was in good condition. Twelve 1st stage compressor stator airfoils fractured at the housing interface, and were liberated from the housing. The remaining airfoils were bent in the direction of compressor rotation, and in an upstream direction away from the 2nd stage rotor. Analysis by the PWC metallurgist revealed that all of the stator airfoils fractured in a ductile manner under shear impact. The chemical composition of the stators met drawing requirements. The hardness of two of the stators was slightly lower than manufacturer's drawing requirements; the other stators met drawing requirements. The 2nd stage compressor stator exhibited nine fractured and liberated airfoils. The remaining airfoils were all bent in the direction of the compressor rotation, and were also bent in a downstream direction away from the 2nd stage rotor. There was damage to both the leading and trailing edges of the airfoils. The 3rd stage compressor stator exhibited one fractured and liberated airfoil. The remaining airfoils exhibited varying degrees of damage on both sides of the airfoil, bent in different directions/angles, and had tip rub with its respective spacer. All three spacers rubbed their respective mating vane tips. The centrifugal impeller had leading edge damage with heavy rub indications along the entire airfoil profile. The centrifugal impeller shroud had a rub mark with material pick up from the impeller. The number one bearing was wet and rotated normally; there was a light rub on the air seals. The number two bearing was wet and rotated normally; the rotor air seal was discolored with displaced material from contact with the stator air seal. Combustion Section The combustion chamber liner was bent, distorted, and twisted; the interior was covered with oil and black carbon. Two areas of the dome were bent. Turbine Section Numerous components of the turbine section were dented and damaged. There were rub marks on various adjacent components. The compressor turbine shroud exhibited a heavy rub mark with both displaced material and metal splatter build up. The power turbine center bore area exhibited dents and distortions. The balancing rim rubbed the PT vane baffle and the anti-rotation lugs were bent. The blade serrations rubbed the baffle. The blades were loose and fractured at varying heights. Metallurgy examination of two randomly selected blades indicated thatthey exhibited tensile overload fractures. No material or overtemperature anomalies were observed; the chemical composition of the blades met drawing requirements. The number three and four bearings of the power turbine shaft and shaft housing were wet and rotated normally, but were stained. The shaft was unremarkable except that it was stained. The number three bearing air seal flange and the number four retention flange bulged forward. Reduction Gearbox The front and rear gearboxes were not disassembled. Both gearboxes rotated freely after the power turbine shaft housing was removed. No visual anomalies were noted. Accessory Gearbox The gearbox was not disassembled; it rotated freely after it was removed from the engine. No visual anomalies were noted. ## Aircraft - Registration: [N7503L](https://openairdocs.org/aircraft/N7503L), registered now, S/N 826B (OpenAirDocs) - Reported make and model: SCHWEIZER AIRCRAFT CORP G-164B - Registry model: [Schweizer G-164B](https://openairdocs.org/model/schweizer-g-164b) (registry code 8059055) (OpenAirDocs) - Registry engine: [Pratt & Whitney R1340 series](https://openairdocs.org/engine/pratt-whitney-r1340-series) (registry code 52016, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 826B - Airframe hours: 10282 - Engines: P&W PT6A-34 600 horsepower turbo prop - Damage: Substantial damage - Flight: Aerial application, Part 137 - Operator: Onstott Dusters Inc - Registered owner: Onstott Dusters Inc - Airworthiness certificate: Special, Restricted (Special) - Last inspection: Annual, April 19, 2011, 373 hours before - Departed: Yuba City, CA - Destination: Yuba City, CA ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 48; injuries: none; commercial; airplane ratings: single-engine land; medical: class 2, with waivers/limitations; last flight review March 18, 2011; seat: single; flight hours: 11,433 total, 5,533 in this make and model, 11,433 as pilot in command, 250 in the last 90 days, 200 in the last 30 days, 15 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 190° at 16 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 91 °F, dew point 61 °F - Altimeter: 29.75 inHg - Observed at: KMYV ## 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 20110709013169A](https://openairdocs.org/incident/20110709013169A), Jul 9, 2011: Schweizer Aircraft Corp G-164B, Yuba City, CA, Substantial damage. The aircraft uplifted a 2000 pound load of fertilizer for disbursement. After takeoff at approximately 30 feet altitude the pilot heard a load bang followed by… ## Other investigations on N7503L (2) 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. - [NTSB WPR25LA158](https://openairdocs.org/ntsb/WPR25LA158), May 9, 2025: Schweizer G-164B (N7503L), Butte City, CA, substantial damage. Probable cause: The pilot’s use of engine beta prior to ensuring the tailwheel was on the ground during landing roll. - [NTSB SEA93LA078](https://openairdocs.org/ntsb/SEA93LA078), Mar 18, 1993: Schweizer G-164B-600 (N7503L), Quincy, WA, substantial damage. Probable cause: UNSUITABLE TERRAIN ENCOUNTERED DURING A FORCED LANDING AFTER AN ENGINE CYLINDER ASSEMBLY HAD SEPARATED. FACTORS INCLUDE A SNOWBANK. ## Docket (5 files) The files NTSB released with the investigation on July 25, 2014, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=81066. 5.8 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 723 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40414337&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - Pratt and Whitney Canada Report (item 2, .PDF, 3.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40414338&FileExtension=.PDF&FileName=Pratt%20and%20Whitney%20Canada%20Report%20-Redacted.PDF - Pratt and Whitney Canada to NTSB Letter (item 3, .PDF, 24 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40414339&FileExtension=.PDF&FileName=Pratt%20and%20Whitney%20Canada%20to%20NTSB%20Letter-Redacted.PDF - Engine Logbook Excerpts (item 4, .PDF, 1.8 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40414344&FileExtension=.PDF&FileName=Engine%20Logbook%20Excerpts%20-Redacted.PDF - PWC Overhaul Manual Excerpts (item 5, .PDF, 146 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40414345&FileExtension=.PDF&FileName=PWC%20Overhaul%20Manual%20Excerpts%20-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.