# NTSB CEN13LA443: Grumman G-164A, N5324, Monte Vista, CO, July 29, 2013 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: July 29, 2013, 07:35 local (13:35 UTC) - Place: Monte Vista, CO - Coordinates: 37.581665, -106.053054 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=37.5817&lon=-106.0531&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute-cruise: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report March 13, 2014 - Report: Approved by Office Director - NTSB office: Central Region - Parties: Federal Aviation Administration - Denver FSDO - ADs cited in the narratives: [AD 99-11-02](https://openairdocs.org/ad/99-11-02) (OpenAirDocs) - NTSB case key (mKey): 87600 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN13LA443 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/87600/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=87600 - Page: https://openairdocs.org/ntsb/CEN13LA443 ## Probable cause The partial loss of engine power due to a fatigue failure of the engine cylinder exhaust rocker housing as a result of an excessively torqued rocker assembly. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Engine (reciprocating): recip eng cyl section](https://openairdocs.org/ntsb-findings/01058530): Aircraft › Aircraft power plant · Fatigue/wear/corrosion (probable cause); cases with it: [Grumman G-164A, 4 cases](https://openairdocs.org/ntsb-findings/01058530/cases.md?model=3952704), [All aircraft, 373 cases](https://openairdocs.org/ntsb-findings/01058530/cases.md) - [Engine (reciprocating): recip eng cyl section](https://openairdocs.org/ntsb-findings/01058530): Aircraft › Aircraft power plant · Failure (probable cause); cases with it: [Grumman G-164A, 4 cases](https://openairdocs.org/ntsb-findings/01058530/cases.md?model=3952704), [All aircraft, 373 cases](https://openairdocs.org/ntsb-findings/01058530/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute-cruise: Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340); cases with it: [Grumman G-164A, 2 cases](https://openairdocs.org/ntsb-events/340/sequence.md?model=3952704), [All aircraft, 820 cases](https://openairdocs.org/ntsb-events/340/sequence.md) - [Enroute-cruise: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) (defining event); cases with it: [Grumman G-164A, 7 cases](https://openairdocs.org/ntsb-events/342/sequence.md?model=3952704), [All aircraft, 1,858 cases](https://openairdocs.org/ntsb-events/342/sequence.md) - [Landing: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Grumman G-164A, 12 cases](https://openairdocs.org/ntsb-events/440/sequence.md?model=3952704), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md) - [Landing: Landing gear collapse](https://openairdocs.org/ntsb-events/094); cases with it: [Grumman G-164A, 4 cases](https://openairdocs.org/ntsb-events/094/sequence.md?model=3952704), [All aircraft, 1,787 cases](https://openairdocs.org/ntsb-events/094/sequence.md) - [Landing: Nose over/nose down](https://openairdocs.org/ntsb-events/096); cases with it: [Grumman G-164A, 11 cases](https://openairdocs.org/ntsb-events/096/sequence.md?model=3952704), [All aircraft, 2,287 cases](https://openairdocs.org/ntsb-events/096/sequence.md) ## Analysis The pilot reported that the aerial-application airplane experienced a partial loss of engine power while en route to the field to be sprayed. He jettisoned the airplane's chemical load following the loss of engine power, but the airplane was unable to maintain altitude and he made a forced landing in a pasture. During the forced landing, the right main landing gear separated from the fuselage after colliding with an irrigation ditch, and the airplane subsequently nosed over. A postaccident examination of the engine revealed a fatigue fracture of the No. 3 cylinder exhaust rocker housing. The measured release torque for the fractured No. 3 exhaust rocker assembly was at the upper limit of that specified by the manufacturer; however, the actual release torque before the failure was likely higher than when measured postaccident. Additionally, a majority of the other rocker assemblies had release torque measurements that exceeded the manufacturer's specified installation limits. Although the overhaul procedures used to assemble the rocker assemblies differed from the manufacturer's overhaul instructions, the investigation was unable to determine if those deviations would have resulted in excessive stress within the rocker housing. However, the investigation did conclude that the fatigue fracture was likely due to an excessive torque loading on the rocker assembly in conjunction with normal rocker operation. A definitive source of the over-torque condition could not be determined. The engine had accumulated 171 hours since being overhauled about 4 months before the accident. A review of the maintenance records found no history of unresolved airworthiness issues with the engine since the last overhaul. Additionally, the airplane owner and the primary maintainer of the airplane stated that no maintenance had been performed on any of the rocker assemblies since the last engine overhaul. A failure of the exhaust rocker housing would result in the corresponding exhaust valve remaining seated during engine operation. Without the typical pathway for the combustion products to be expelled through the engine exhaust, the hot gases would ignite the fuel/air mixture within the engine intake manifold. The likely result of a rocker housing failure would be an immediate and significant loss of engine power. ## Factual narrative On July 29, 2013, at 0735 mountain daylight time, a Grumman model G-164A airplane, N5324, was substantially damaged during a forced landing following a loss of engine power near Monte Vista, Colorado. The airline transport pilot was not injured. The airplane was registered to and operated by Crop Care Inc., under the provisions of 14 Code of Federal Regulations Part 137, without a flight plan. Day visual meteorological conditions prevailed for the local aerial application flight that departed Monte Vista Municipal Airport (MVI), Monte Vista, Colorado, about 0730. The pilot reported that the airplane experienced a partial loss of engine power while en route to the field to be sprayed. He jettisoned the airplane's chemical load following the loss of engine power, but the airplane was unable to maintain altitude and a forced landing was made in a pasture. During the forced landing, the right main landing gear separated from the fuselage after colliding with an irrigation ditch and the airplane subsequently nosed over. The airframe and wings sustained substantial damage during the forced landing. The accident engine, a Pratt & Whitney model R-1340-AN-1, serial number ZP-102893, was last overhauled by Covington Aircraft Engines Inc. of Okmulgee, Oklahoma, on March 21, 2013. At the time of overhaul, the engine had accumulated about 10,125 hours since new. The overhauled engine was installed on the accident airplane on May 1, 2013, and had accumulated about 171 hours when the accident occurred. A postaccident examination of the engine revealed a fracture of the No. 3 cylinder exhaust rocker housing. The entire cylinder was shipped to the National Transportation Safety Board (NTSB) Materials Laboratory for additional examination. The NTSB laboratory report indicated that the observed fracture extended from the rocker cap on the inside of the rocker housing to the rocker shaft, from the inner end of the rocker shaft around the housing to the outer end of the rocker shaft, and from the outer end of the rocker shaft to the rocker cap. The upper portion of the exhaust housing revealed two discolored zones on the inner surface of the outer side, consistent with a prolong exposure to the atmosphere. Additional examination of those discolored zones revealed arced edges that were consistent with fatigue. The rocker assembly hardware from the No. 3 cylinder consisted of the shaft, the large castellated nut with a red O-ring seal, and the small castellated nut with a washer and black O-ring seal. The rocker assembly was consistent with the component breakdown found in the manufacturer's illustrated parts catalog. The rocker hardware was removed from the upper portion of the exhaust housing and the torque required to loosen the small nut (release torque) measured 250 inch-pounds (in-lbs). A review of the manufacturer's overhaul instructions for the rocker assemblies indicated that the large castellated nut, including the red O-ring seal, is first installed on theshaft and rotated until the flats on the large end of the shaft are exposed enough for an open ended wrench to be engaged on them. The small end of the shaft is then inserted into the large bushing, through the rocker, and finally through the small bushing. The black O-ring seal, washer, and small castellated nut are then installed and the nut torqued to 200-250 in-lbs. The small nut is then further tightened to the next slot in the castellated nut. The large nut, with the red O-ring seal, is tightened until it is snug against the shoulder of the bushing, and then further tightened to the next slot in the castellated nut. The final assembly is secured by inserting a cotterpin in each castellated nut. (An alternative assembly procedure is used when a copper-covered gasket is installed under the large castellated nut, followed by an oil seal against the shoulder of the bushing. The large castellated nut is initially torqued to 60-100 in-lbs when the alternative procedure is used.) The cylinder inspection and assembly procedures used by the overhaul facility (Covington Aircraft Engines Inc.) were reviewed by a NTSB powerplant specialist. The overhaul facility's cylinder inspection procedures were in compliance with Pratt & Whitney Service Bulletin (SB) 1785 and Federal Aviation Administration (FAA) Airworthiness Directive (AD) 99-11-02. The observed rocker assembly differed from the manufacturer's overhaul instructions. The assembly procedure used by the overhaul facility was to first install the shaft, small end first, into the large bushing, through the rocker, and finally through the small bushing. The black O-ring seal, washer, and small castellated nut were then installed on the small end of the shaft. The small nut was torqued to 200 in-lbs before being further tightened to the next slot in the castellated nut. The red O-ring seal and large castellated nut were then installed on the opposite end of the shaft. The large nut was torqued to 80 in-lbs before being further tightened to the next slot in the castellated nut. The final assembly was secured by inserting a cotterpin in each castellated nut. (The observed assembly procedure included torque loading of the large castellated nut to 80 in-lbs; however, a red O-ring seal was installed under the large nut instead of the copper-covered gasket specified in the manufacturer's alternative assembly instructions.) According to the manufacturer's illustrated part catalog, the same components were used for the intake and exhaust rocker assemblies. Additionally, the manufacturer's overhaul manual specified the same assembly procedure for both rocker assemblies. The release torque for the small nut was measured for the intake and exhaust rocker assemblies on the remaining cylinders of the accident engine. The recorded values ranged between 78 in-lbs and 546 in-lbs; however, a majority of the recorded values were in excess of 300 in-lbs. The intake and exhaust rocker assemblies for cylinder Nos. 3 and 4were reassembled in accordance with the assembly instructions contained in the overhaul manual. The small nut was torqued to 225 in-lbs (midway between the specified range of 200-250 in-lbs), and then further tightened to the next slot in the castellated nut. The large nut, with the red O-ring seal, was hand tightened until it was snug against the shoulder of the large bushing, and then further tightened to the next slot in the castellated nut. After assembly, the release torque was measured for each rocker assembly. The recorded values ranged between 175 in-lbs and 220 in-lbs. A review of the maintenance records found no history of unresolved airworthiness issues with the engine since the last overhaul. Additionally, the airplane owner and the primary maintainer of the airplane stated that no maintenance had been performed on any of the rocker assemblies since the last engine overhaul. ## Aircraft - Registration: [N5324](https://openairdocs.org/deregistered/N5324-2014-01-23), registration cancelled 2014-01-23, S/N 606, built 1969 (OpenAirDocs) - Reported make and model: GRUMMAN G-164A - Registry model: [Grumman G-164A](https://openairdocs.org/model/grumman-g-164a) (registry code 3952704) (OpenAirDocs) - Registry engine: [Pratt & Whitney R1340 series](https://openairdocs.org/engine/pratt-whitney-r1340-series) (registry code 52016, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 606 - Year built: 1969 - Airframe hours: 11330.3 - Engines: Pratt & Whitney R1340 600 horsepower reciprocating - Damage: Substantial damage - Flight: Aerial application, Part 137 - Operator: Crop Care Inc. - Registered owner: Crop Care Inc. - Airworthiness certificate: Special, Restricted (Special) - Last inspection: Annual, May 1, 2013, 171 hours before - Departed: MVI, Monte Vista, CO - Destination: MVI, Monte Vista, CO ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 66; injuries: none; flight instructor, airline transport; airplane ratings: multi-engine land, single-engine sea, single-engine land; instrument ratings: airplane; medical: class 2, with waivers/limitations; last flight review December 22, 2012; seat: single; restraint: 4-point; flight hours: 25,256 total, 4,500 in this make and model, 20,000 as pilot in command, 180 in the last 90 days, 3 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 290° at 3 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 54 °F, dew point 52 °F - Altimeter: 30.26 inHg - Observed at: ALS, 12 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 20130729021349A](https://openairdocs.org/incident/20130729021349A), Jul 29, 2013: Grumman G-164A, Monte Vista, CO, Substantial damage. On 07/29/2013 at approximately 0735 hours MDT, N5324 a Grumman ag cat model G-164A aircraft was substantially damaged after an off-airport landing near Monte… ## Other investigations on N5324 (3) 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 DEN86LA220](https://openairdocs.org/ntsb/DEN86LA220), Aug 5, 1986: Grumman G-164A (N5324), Center, CO, substantial damage - [NTSB FTW70FRA36](https://openairdocs.org/ntsb/FTW70FRA36), Jun 26, 1970: Grumman G-164A (N5324), Rosharon, TX, substantial damage - [NTSB FTW69D0501](https://openairdocs.org/ntsb/FTW69D0501), May 9, 1969: Grumman G-164A (N5324), Rosharon, TX, substantial damage ## Docket (12 files) The files NTSB released with the investigation on December 19, 2013, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=87600. 6.3 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 374 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40406749&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - Local Law Enforcement Statement (item 2, .PDF, 107 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40406750&FileExtension=.PDF&FileName=Local%20Law%20Enforcement%20Statement-Redacted.PDF - Photograph of Engine at Accident Site (item 3, .PDF, 1.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40406756&FileExtension=.PDF&FileName=Photograph%20of%20Engine%20at%20Accident%20Site-Master.PDF - Engine Logbook Excerpts (item 4, .PDF, 195 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40406751&FileExtension=.PDF&FileName=Engine%20Logbook%20Excerpts-Redacted.PDF - Email Correspondence (item 5, .PDF, 92 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40406752&FileExtension=.PDF&FileName=Email%20Correspondence-Redacted.PDF - Materials Laboratory - Factual Report No. 13-098 (item 6, .PDF, 19 photos, 2.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40406740&FileExtension=.PDF&FileName=Materials%20Laboratory%20-%20Factual%20Report%20No.%2013-098-Master.PDF - Maintenance Records - Factual Report of Group Chairman (item 7, .PDF, 4 photos, 822 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40405682&FileExtension=.PDF&FileName=Maintenance%20Records%20-%20Factual%20Report%20of%20Group%20Chairman-Master.PDF - Maintenance Records - Attachment 1 (item 8, .PDF, 102 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40403519&FileExtension=.PDF&FileName=Maintenance%20Records%20%20-%20Attachment%201-Master.PDF - Maintenance Records - Attachment 2 (item 9, .PDF, 373 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40403522&FileExtension=.PDF&FileName=Maintenance%20Records%20-%20Attachment%202-Master.PDF - Maintenance Records - Attachment 3 (item 10, .PDF, 337 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40403524&FileExtension=.PDF&FileName=Maintenance%20Records%20-%20Attachment%203-Master.PDF - Maintenance Records - Attachment 4 (item 11, .PDF, 273 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40403526&FileExtension=.PDF&FileName=Maintenance%20Records%20-%20Attachment%204-Master.PDF - Maintenance Records - Attachment 5 (item 12, .PDF, 95 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40403528&FileExtension=.PDF&FileName=Maintenance%20Records%20-%20Attachment%205-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.