# NTSB WPR17LA176: Cessna 172S, N957TA, Seattle, WA, July 31, 2017 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Class 3 · Limited · Final report - Date: July 31, 2017, 12:30 local (19:30 UTC) - Place: Seattle, WA - Coordinates: 47.54861, -122.40139 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=47.5486&lon=-122.4014&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute-cruise: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) - Highest injury: Minor injuries - Injuries: 2 minor - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Western Pacific Region - Parties: Federal Aviation Administration, Lycoming Engines - NTSB case key (mKey): 95729 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR17LA176 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/95729/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=95729 - Page: https://openairdocs.org/ntsb/WPR17LA176 ## Probable cause The total loss of engine power due to oil starvation as a result of the loose right magneto, which allowed oil to escape and the engine to seize. Contributing to the accident was inadequate maintenance, which failed to identify the loose magneto bolt. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Fluids: oil](https://openairdocs.org/ntsb-findings/01071020): Aircraft › Fluids/misc hardware · Fluid level (probable cause); cases with it: [Cessna 172S, 1 case](https://openairdocs.org/ntsb-findings/01071020/cases.md?model=2072439), [All aircraft, 174 cases](https://openairdocs.org/ntsb-findings/01071020/cases.md) - [Fluids: oil](https://openairdocs.org/ntsb-findings/01071020): Aircraft › Fluids/misc hardware · Related maintenance info (probable cause); cases with it: [Cessna 172S, 1 case](https://openairdocs.org/ntsb-findings/01071020/cases.md?model=2072439), [All aircraft, 174 cases](https://openairdocs.org/ntsb-findings/01071020/cases.md) - [Maintenance: scheduled/routine maintenance](https://openairdocs.org/ntsb-findings/02062010): Personnel issues › Task performance · Maintenance personnel (probable cause); cases with it: [Cessna 172S, 1 case](https://openairdocs.org/ntsb-findings/02062010/cases.md?model=2072439), [All aircraft, 320 cases](https://openairdocs.org/ntsb-findings/02062010/cases.md) - [Engine (reciprocating): recip eng rear section](https://openairdocs.org/ntsb-findings/01058540): Aircraft › Aircraft power plant · Incorrect service/maintenance (probable cause); cases with it: [Cessna 172S, 2 cases](https://openairdocs.org/ntsb-findings/01058540/cases.md?model=2072439), [All aircraft, 42 cases](https://openairdocs.org/ntsb-findings/01058540/cases.md) - [Ignition system: magneto/distributor](https://openairdocs.org/ntsb-findings/01057414): Aircraft › Aircraft power plant · Incorrect service/maintenance (probable cause); cases with it: [Cessna 172S, 1 case](https://openairdocs.org/ntsb-findings/01057414/cases.md?model=2072439), [All aircraft, 101 cases](https://openairdocs.org/ntsb-findings/01057414/cases.md) - [Terrain: water](https://openairdocs.org/ntsb-findings/03021020): Environmental issues › Physical environment · Contributed to outcome (probable cause); cases with it: [Cessna 172S, 3 cases](https://openairdocs.org/ntsb-findings/03021020/cases.md?model=2072439), [All aircraft, 97 cases](https://openairdocs.org/ntsb-findings/03021020/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute-cruise: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) (defining event); cases with it: [Cessna 172S, 19 cases](https://openairdocs.org/ntsb-events/341/sequence.md?model=2072439), [All aircraft, 3,820 cases](https://openairdocs.org/ntsb-events/341/sequence.md) - [Enroute-cruise: Emergency descent initiated](https://openairdocs.org/ntsb-events/130); cases with it: [Cessna 172S, 1 case](https://openairdocs.org/ntsb-events/130/sequence.md?model=2072439), [All aircraft, 42 cases](https://openairdocs.org/ntsb-events/130/sequence.md) - [Landing-flare/touchdown: Ditching](https://openairdocs.org/ntsb-events/441); cases with it: [Cessna 172S, 1 case](https://openairdocs.org/ntsb-events/441/sequence.md?model=2072439), [All aircraft, 186 cases](https://openairdocs.org/ntsb-events/441/sequence.md) - [Landing-flare/touchdown: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [Cessna 172S, 118 cases](https://openairdocs.org/ntsb-events/470/sequence.md?model=2072439), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis During an instructional flight, the engine started running rough and, shortly after the oil pressure light illuminated, subsequently quit. The pilot elected to ditch the airplane in the water close to the shoreline. An onsite examination of the engine revealed that the top bolt of the right magneto was loose and had backed off, which allowed the magneto to become partially separated, leaving a 3/8-inch gap at the top of the magneto where it mounted to the case, which allowed oil to exit the engine. Metal shavings were observed throughout the engine. A review of the maintenance records indicated that the magnetos were removed and overhauled about 9 months before the accident during a 500-hour inspection, which was 420.5 hours of flight time before the accident. The airplane had accumulated about 22 hours of flight time since its last annual inspection, and the loose magneto bolt should have been able to be identified at that time. ## Factual narrative On July 31, 2017, about 1230 Pacific daylight time, a Cessna 172S, N957TA, was substantially damaged in an accident about 5 nautical miles northwest of Seattle International Airport (SEA), Seattle, Washington. The flight instructor and student pilot receiving instruction sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The flight instructor reported that after completing air work they were returning to Boeing Field/King County International Airport (BFI), Seattle, Washington, when the engine started running rough. During the descent, the engine started to run rougher and it continued to lose rpm. Shortly thereafter the low oil pressure light illuminated, and 10 to 15 seconds later the engine quit. When the pilot attempted to restart the engine and the propeller would not move, he elected to ditch the airplane in the water close to the shoreline; the landing resulted in the deformation of the engine mount. The following day the airplane was recovered to a secured facility for further examination. According to a Federal Aviation Administration (FAA) aviation safety inspector who was on site during the recovery process the day following the accident, as the airplane was removed from the water and the engine cowling was removed, he observed that the top bolt of the right magneto was loose and had backed off, which created a 3/8" gap between the magneto and its mounting pad. An external visual examination of the engine revealed no catastrophic damage; however, the engine was seized and would not rotate. The muffler was damaged slightly, the right magneto was canted aft from its mounting pad at the top right position, with the attachment nut observed loose. The lower mounting nut was loose at the bottom of the mount. There were 4 accessory case bolts missing from the accessory case, three from the right side at the bottom of the case, one on the left bottom and one bolt on the left side was protruding halfway out. When the loose right magneto was removed from its mounting pad, there was no noticeable damage to the magneto gear, although there were metal flakes observed inside the magneto, and its gasket was torn. When the left magneto was removed, it was observed to be tight in its mount; metal flakes were detected on the gears. The remainder of the accessories were removed from the accessory section of the engine. While no damage was observed to any of the accessories, metal flakes were detected within and around them. After the accessory case bolts had been removed, a visual inspection of each bolt revealed no stress signatures to their respective threads. An examination of the right magneto's top right bolt that had backed out, revealed that no stress signatures were observed on the bolt's threads. During removal of the accessory case bolts, it was observed that more than half of the bolts were not tight. The manufacturer's maintenance manual stipulates that all bolts shouldbe properly torqued; the bolts have a star lock washer, however, no safety wire. No stress was found on any of the bolt threads or their respective mount threads. Each bolt had the appropriate washer. When the engine case was disassembled, it was observed that the crankshaft had broken in half at the middle bearing. A large section of the crankshaft had separated, which was subsequently located in the bottom of the case. When the crankshaft was removed, it was observed that the bearing had become welded to the shaft. Additionally, heat stress signatures were observed. A representative of the engine manufacturer reported that based on the findings, it was his opinion that when the right magneto came loose and backed out of its mount, it allowed all of the oil to exit at the magneto mounting hole. Maintenance records revealed that the zero-time rebuilt engine was installed on the airplane, December 29, 2015. At the time of the accident, the engine had accumulated a total of 917.5 hours, with 22.4 hours since its last annual inspection, dated July 25, 2017. It was noted that both the left and right magnetos were removed and overhauled on November 3, 2016, during a 500-hour inspection, which was 497 hours after the engine was installed, and 420.5 hours before the failure of the engine. Maintenance records also revealed that 122 hours before the accident, the accessory case was removed in order to replace the oil pump body, as well as the drive and impeller. When the case was removed during the examination of the engine, there were no anomalies noted with any of the previously referred to components. ## Aircraft - Registration: [N957TA](https://openairdocs.org/deregistered/N957TA-2018-01-18), registration cancelled 2018-01-18, S/N 172S9057, built 2002 (OpenAirDocs) - Reported make and model: CESSNA 172S (S) - Registry model: [Cessna 172S](https://openairdocs.org/model/cessna-172s) (registry code 2072439) (OpenAirDocs) - Registry engine: [Continental IO-360 series](https://openairdocs.org/engine/continental-io-360-series) (registry code 17025, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 172S9057 - Year built: 2002 - Airframe hours: 5539.9 - Engines: Lycoming IO-360-L2R 180 horsepower reciprocating - Damage: Substantial damage - Flight: Instructional, Part 91 - Airworthiness certificate: Standard, Normal - Last inspection: 100 hour, July 25, 2017, 22 hours before - Departed: BFI, Seattle, WA - Destination: BFI, Seattle, WA - Equipment: Stall warning system ## Flight crew As NTSB recorded them. NTSB leaves out names. - Flight instructor; age 24; injuries: minor; commercial; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 1, without waivers/limitations; last flight review April 4, 2017; seat: right; restraint: 3-point; flight hours: 490 total, 57 in this make and model, 373 as pilot in command, 206 in the last 90 days, 64 in the last 30 days, 1 in the last 24 hours - Student pilot; age 30; injuries: minor; student; medical: class 3, without waivers/limitations; seat: left; restraint: 3-point; flight hours: 0 total, 0 in this make and model ## Weather - Conditions: Visual (VMC), Day - Wind: 10° at 10 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 79 °F, dew point 52 °F - Altimeter: 30.23 inHg - Observed at: BFI, 5 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). - [Accident 20170731010209A](https://openairdocs.org/incident/20170731010209A), Jul 31, 2017: Cessna 172S, West Seattle, WA, Substantial damage. Engine had a catastrophic failure during descent to Boeing field when the crank shaft completely seprated at approximately its midpoint. Instructor pilot… ## Docket (8 files) The files NTSB released with the investigation on August 24, 2020, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=95729. 5.2 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 1.6 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40486275&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Record of Telephone Conversation between FAA and Lycoming Engines (item 2, .PDF, 20 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40486276&FileExtension=.PDF&FileName=Record%20of%20Telephone%20Conversation%20between%20FAA%20and%20Lycoming%20Engines-Master.PDF - Engine Examination Notes (item 3, .PDF, 964 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40486277&FileExtension=.PDF&FileName=Engine%20Examination%20Notes-Master.PDF - Excerpts from Engine Logbooks (item 4, .PDF, 765 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40486278&FileExtension=.PDF&FileName=Excerpts%20from%20Engine%20Logbooks-Master.PDF - Statement of Party Representatives to NTSB Investigation (item 5, .PDF, 135 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40486279&FileExtension=.PDF&FileName=Statement%20of%20Party%20Representatives%20to%20NTSB%20Investigation-Master.PDF - Release of Aircraft Wreckage, NTSB Form 6120.15 (item 6, .PDF, 259 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40486280&FileExtension=.PDF&FileName=Release%20of%20Aircraft%20Wreckage,%20NTSB%20Form%206120.15-Master.PDF - Evidence Control Form (item 7, .PDF, 347 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40486281&FileExtension=.PDF&FileName=Evidence%20Control%20Form-Master.PDF - Photo Array (item 8, .PDF, 1.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40486282&FileExtension=.PDF&FileName=Photo%20Array-Master.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.