# NTSB WPR11LA102: Piper PA-28-235, N8608W, San Luis Obispo, CA, January 20, 2011 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: January 20, 2011, 13:17 local (21:17 UTC) - Place: San Luis Obispo, CA - Coordinates: 35.23722, -120.509162 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=35.2372&lon=-120.5092&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute-descent: Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report January 17, 2012 - Report: Approved by Office Director - NTSB office: Western Pacific Region - Parties: Federal Aviation Administration, Textron Lycoming Engines, Piper Aircraft - NTSB case key (mKey): 78200 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR11LA102 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/78200/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=78200 - Page: https://openairdocs.org/ntsb/WPR11LA102 ## Probable cause The loss of engine power due to the fatigue fracture of one attachment bolt for the left idler gear shaft, which resulted from an insufficient preload on both attachment bolts. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Engine (reciprocating): recip eng rear section](https://openairdocs.org/ntsb-findings/01058540): Aircraft › Aircraft power plant · Fatigue/wear/corrosion (probable cause); cases with it: [Piper PA-28-235, 2 cases](https://openairdocs.org/ntsb-findings/01058540/cases.md?model=7102810), [All aircraft, 42 cases](https://openairdocs.org/ntsb-findings/01058540/cases.md) - [Engine (reciprocating): recip eng rear section](https://openairdocs.org/ntsb-findings/01058540): Aircraft › Aircraft power plant · Malfunction (probable cause); cases with it: [Piper PA-28-235, 2 cases](https://openairdocs.org/ntsb-findings/01058540/cases.md?model=7102810), [All aircraft, 42 cases](https://openairdocs.org/ntsb-findings/01058540/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute-descent: Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340) (defining event); cases with it: [Piper PA-28-235, 1 case](https://openairdocs.org/ntsb-events/340/sequence.md?model=7102810), [All aircraft, 820 cases](https://openairdocs.org/ntsb-events/340/sequence.md) - [Enroute-descent: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341); cases with it: [Piper PA-28-235, 16 cases](https://openairdocs.org/ntsb-events/341/sequence.md?model=7102810), [All aircraft, 3,820 cases](https://openairdocs.org/ntsb-events/341/sequence.md) ## Analysis The pilot reported that, while on approach to the runway, the vacuum pump failed, then the engine lost power. The pilot initiated a forced landing to a field, and the airplane impacted multiple metal poles. Postaccident examination of the engine revealed that the left magneto drive gear and the left idler gear shaft were separated from their mount. Both of the attachment bolts for the left idler gear shaft were separated from the crankcase, and their respective bolt bores were elongated. One of the attachment bolts for the left idler gear shaft was fractured, and metallurgical examination revealed that the fracture surface was consistent with fatigue. Metallurgical analysis determined that the fatigue was due to a lack of sufficient preload on the bolts. Maintenance records showed that the last logged maintenance activity in which the bolts could have been manipulated was performed about 20 years before the accident. The engine had accumulated about 1,400 operating hours since that time. ## Factual narrative On January 20, 2011, about 1317 Pacific standard time, a Piper PA-28-235, N8608W, sustained substantial damage during a forced landing near the San Luis County Regional Airport (SBP), San Luis Obispo, California. The airplane was registered to and operated by the pilot under the provisions of Title 14 Code of Federal Regulations Part 91. The private pilot, sole occupant of the airplane, was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the personal flight. The local flight originated from SBP at 1130. The pilot reported that while on approach to runway 29, he noticed that the vacuum pump failed. The pilot continued flying towards SBP, and was asked by air traffic control to slow the airplane for traffic ahead of his position. The pilot said that he reduced power to comply with the controller's request. Shortly after, the pilot advanced the throttle to arrest the descent, and noticed the engine did not respond. The pilot said that he realized the engine had lost power, and that he would not be able to make the airport, so he initiated a forced landing to a field adjacent to his position. During the forced landing, the airplane impacted multiple metal poles within a vineyard and came to rest upright. Examination of the airplane by a Federal Aviation Administration (FAA) inspector revealed that the left and right wings sustained structural damage. All four fuel tanks (auxiliary and main) were breeched. The odor of fuel was present at the accident site after the time of the accident. The airplane was recovered to a secure location for further examination. Examination of the recovered engine revealed that it remained attached to the airframe via all mounts. All fuel lines, throttle, and mixture control cables were intact and remained attached to the engine. The top spark plugs were removed and remained free of mechanical damage. The top spark plugs exhibited coloration consistent with normal operation. The propeller was rotated by hand in the direction of normal rotation. No movement of the intake and exhaust rocker arms was observed. In addition, no magneto impulse couplings were heard clicking, and the vacuum pump drive was not rotating. The engine was removed from the airframe and placed on a bench. The left and right magneto, vacuum pump, oil filter, and rear accessory cover were removed from the engine. The left magneto drive gear and the left idle gear shaft were observed loose from their mount. Both bolts were separated from the crankcase, and their respective bolt bores were elongated. Heavy fretting, gouging, and smearing was observed around the mounting surface for the left idler magneto gear drive shaft. Fragmented remains of the safety locking plate and bolts were located within the oil sump. The idler gear shaft, locking plate, and bolts were retained for further examination. The oil filter was cut open, and the internal element was examined. Metallic fragments were observed throughout the oilfilter element. The oil suction screen was removed, and found to be free of any significant debris. The left crankshaft idler gear shaft, fragments of the locking plate, and two bolts were subsequently sent to the National Transportation Safety Board Materials Laboratory, Washington DC, for further examination. Examination of the components by a Materials Engineer revealed impact wear and deformation was observed around a mounting hole in the idler gear shaft flange, which is consistent with battering associated with a loose bolt. The locking plate was fractured in several areas and was heavily distorted. The holes in the locking plate were elongated and enlarged. Metal transfer and impact wear was also observed around the holes. The upper and lower ends of the plate were bent 90 degrees to form around the bolt heads. The fracture surface features of the locking plate were found consistent with an overstress fracture. Both bolt heads exhibited similar impact wear damage, however the impact wear damage was most pronounced on the fractured bolt. The hexagonal corners of the bolt heads were rounded, which was consistent with impact wear. The grip region below the head of the fractured bolt was elongated, and the grip diameter was reduced to about 60 percent of its original diameter. This dimensional deformation appeared to have smooth edges consistent with necking. The bolt was fractured in this reduced-diameter area. Around the circumference of the fracture face, the bolt was worn uniformly, consistent with impact wear from metal-to-metal contact. A portion of the fracture had relatively smooth features on flat planes perpendicular to the bolt axis, and exhibited curved crack arrest marks, consistent with fatigue cracking. Ratchet marks were observed around the circumference, consistent with multiple origins. At its deepest penetration, the fatigue crack had propagated approximately 95 percent through the diameter of the fracture surface. The remainder of the fracture exhibited features consistent with overstress separation. There was a visible crack in the grip region of the intact bolt that propagated nearly 200 degrees around the circumference. The axial location of this crack is in a similar location to the fracture in the fractured bolt. This crack was lab fractured to reveal a fracture surface. A small portion of the fracture had relatively smooth features on flat planes, and showed curved crack arrest marks, consistent with fatigue cracking. Ratchet marks were observed over a small area around the circumference, indicating multiple origins. The fatigue had propagated approximately 10 percent across the fracture diameter. The remainder of the fracture exhibited features consistent with overstress separation. Review of the airplane maintenance records revealed that the engine was overhauled on April 7, 1990, at a tachometer time of 248.8 hours. The most recent 100-hour inspection was conducted on March 23, 2010, at a tachometer time of1,609.5 hours and an engine total time of 3,504.4 hours and 1,373.77 hours since major overhaul. No logbooks entries were observed concerning the idler gear shaft mounting bolts or lock plate. ## Aircraft - Registration: [N8608W](https://openairdocs.org/deregistered/N8608W-2012-02-25), registration cancelled 2012-02-25, S/N 28-10124, built 1963 (OpenAirDocs) - Reported make and model: PIPER PA-28-235 - Registry model: [Piper PA-28-235](https://openairdocs.org/model/piper-pa-28-235) (registry code 7102810) (OpenAirDocs) - Registry engine: [Lycoming 0-540 series](https://openairdocs.org/engine/lycoming-0-540-series) (registry code 41532, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 28-10124 - Airframe hours: 3505 - Engines: LYCOMING O-540 SERIES 250 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Operator: Elliott Clifford R Trustee - Registered owner: Elliott Clifford R Trustee - Airworthiness certificate: Standard, Normal - Last inspection: Annual, March 23, 2010, 46 hours before - Departed: SBP, San Luis Obispo, CA - Destination: SBP, San Luis Obispo, CA - Airport: SBP, San Luis County Airport ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 42; injuries: none; commercial; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 3, with waivers/limitations; last flight review March 23, 2010; seat: left; flight hours: 2,029 total, 1,027 in this make and model, 1,874 as pilot in command, 15 in the last 90 days, 5 in the last 30 days ## Weather - Conditions: Visual (VMC), Day - Wind: variable at 4 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 72 °F, dew point 45 °F - Altimeter: 30.07 inHg - Observed at: SBP, 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). - [Accident 20110120000429A](https://openairdocs.org/incident/20110120000429A), Jan 20, 2011: Piper PA-28-235, San Luis Obispo, CA, Substantial damage. On 01/20/2011 at 1315 PST, Piper cherokee (N8608W) was inbound to the San Luis Obispo regional airport. While on final approach, air traffic control (ATC)… ## Other investigations on N8608W (1) 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 LAX67D0143](https://openairdocs.org/ntsb/LAX67D0143), Sep 23, 1966: Piper PA-28 (N8608W), Mt.Trumble, AZ, substantial damage ## Docket (8 files) The files NTSB released with the investigation on November 28, 2011, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=78200. 5.4 MB in all. - Materials Laboratory Factual Report 11-068 (with 6 embedded images) (item 1, .PDF, 6 photos, 1.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40353884&FileExtension=.PDF&FileName=Materials%20Laboratory%20Factual%20Report%2011-068%20(with%206%20embedded%20images)-Master.PDF - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 2, .PDF, 502 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40355780&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - Summary of Engine Examination (item 3, .PDF, 54 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40355781&FileExtension=.PDF&FileName=Summary%20of%20Engine%20Examination-Master.PDF - Statement of Party Representatives to NTSB Investigation - Lycoming Engines (item 4, .PDF, 649 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40358440&FileExtension=.PDF&FileName=Statement%20of%20Party%20Representatives%20to%20NTSB%20Investigation%20-%20Lycoming%20Engines-Redacted.PDF - Statement of Party Representatives to NTSB Investigation - Piper Aircraft (item 5, .PDF, 91 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40358441&FileExtension=.PDF&FileName=Statement%20of%20Party%20Representatives%20to%20NTSB%20Investigation%20-%20Piper%20Aircraft-Redacted.PDF - Release of Aircraft Wreckage, NTSB Form 6120.15 (item 6, .PDF, 30 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40357383&FileExtension=.PDF&FileName=Release%20of%20Aircraft%20Wreckage,%20NTSB%20Form%206120.15-Redacted.PDF - Photo 1: View of the rear of the engine accessory gear section. (item 7, .PDF, 1.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40355782&FileExtension=.PDF&FileName=Photo%201%3A%20View%20of%20the%20rear%20of%20the%20engine%20accessory%20gear%20section.-Master.PDF - Photo 2: View of the rear of the engine accessory gear section. (item 8, .PDF, 1.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40355783&FileExtension=.PDF&FileName=Photo%202%3A%20View%20of%20the%20rear%20of%20the%20engine%20accessory%20gear%20section.-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.