Romona, CA, USA
N3997Y
Cessna 210
The airplane engine’s rpm became erratic, and the pilot decided to divert. About 5 miles from the intended airport, the airplane began to shake, and the pilot made an off-airport landing. Postaccident examination revealed several holes in the engine crankcase. The oil filter adapter was found loose, and the fiber gasket was protruding beyond the castings. Removal of the oil filter adapter revealed that the fiber gasket had torn. The failure of the fiber gasket allowed oil to exit the engine, resulting in oil starvation and a subsequent total loss of engine power. During postaccident testing, the gasket failure in the accident adapter could not be replicated, and the reason for the failure could not be determined. The testing did reveal that the adapters were difficult to install properly and that, when the proper torque was achieved, the adapter housing could still be rotated about its hub when manual pressure was applied, indicating that the housing was loose. In response to this accident investigation, the supplemental type certificate holder issued a service bulletin that stated that the adapter should be inspected for oil leakage and gasket damage. The service bulletin also provided detailed instructions to eliminate rotation of the housing during installation and identify rotation after installation. In addition, the Federal Aviation Administration issued an airworthiness directive that requires operators to replace the oil filter adapter fiber gasket with a copper gasket to prevent an engine power loss due to oil starvation.
HISTORY OF FLIGHTOn June 10, 2019, about 1245 Pacific daylight time, a Cessna 210D airplane, N3997Y, was substantially damaged when it was involved in an accident near Ramona, California. The pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot stated that the airplane had departed from Gillespie Field (SEE), El Cajon, California, and that he was planning to practice a VOR approach to the airport. While the airplane was at an altitude of about 6,000 ft mean sea level (msl), the engine speed increased to above 3,000 rpm. In response, the pilot retarded the propeller control to 2,400 rpm. The pilot thought that the increase in engine rpm was due to a propeller governor anomaly and told an air traffic controller that he was terminating the practice approach and would be returning to SEE. When the airplane was about 5 miles south of Ramona Airport (RMN), Ramona, California, the pilot felt the airplane begin to shake, and he declared an emergency to the RMN air traffic control tower. The engine lost power, and the airplane touched down in a field about 1/8 mile short of runway 27 at RMN. During the touchdown, the airplane sustained damage to the right wing. AIRCRAFT INFORMATIONThe overhauled engine was installed in the airplane in June 2003 at an airplane total time of 1,119 hours. Engine Oil Filter Adapter Design The engine was equipped with an F&M Enterprises Inc. engine oil filter adapter, model C6LC L, which was installed under Federal Aviation Administration (FAA) Supplemental Type Certificate (STC) SE09356SC. The current STC holder, Stratus Tool Technologies (owned by Aero Accessories Inc.), purchased the STC from F&M Enterprises about 5 years before the accident. The complete certification package for the STC could not be found by the FAA Aircraft Certification Office. The purpose of the adapter was to enable the engine to use a conventional spin-on oil filter. As manufactured, the oil pump was equipped with a brass oil screen mounted to the casing; the filter adapter used the oil screen bore to attach to the engine. The adapter included a tee casting (housing) and a hub (shaft), which was threaded into the oil screen hole on the engine's oil pump casting. The tee casting had a sleeve with a through-bore and a mounting base that was threaded so that a spin-on oil filter could be attached. A crown (1-inch bolt head) at the outboard end of the shaft secured the tee casting against the oil pump casing. A copper gasket was placed between the crown and the outboard surface of the sleeve's bore; a fiber gasket was placed between the oil pump casting and the inboard surface of the sleeve's bore. Oil inlet and oil outlet passages are provided through the hub and the tee casting to circulate oil from the oil screen hole to the spin-on filter and vice versa (see figure 1). Figure 1. Oil filter adapter. The adapter was originally designed to use two AN900-200 copper gaskets. At an unknown time and for an unknown reason, F&M Enterprises changed the gasket between the oil pump casting and the inboard surface of the sleeve’s bore to a fiber gasket. The fiber gasket, part no. FM07, was manufactured from 3750 Leak-Guard material produced by Garlock; the last order that F&M Enterprises placed for the gasket was in July 2013. Stratus Tool Technologies stated that, since the time that it purchased the STC, fiber gaskets have been ordered from Corley Gasket Company, which has not had any FAA oversight. According to the accident airplane owner, the oil filter adapter was likely installed on the then-newly overhauled engine in June 2003. No documents were found regarding the installation of the adapter, but the adapter was mentioned in logbook entries from March 2004 and January 2007. STC Holders' Installation Instructions According to records that Stratus Tool Technologies provided, at the time that the accident oil filter adapter was installed in May 2019, the Instructions for Continued Airworthiness for the oil filter adapter assembly (which had last been published in October 2013) stated, in part, "new gaskets are to be installed anytime the oil filter adapter assy [assembly] is removed and re-installed" and "replace gaskets at 300 hours or 3 yrs whichever occurs first." The Instructions for Continued Airworthiness further stated to "refer to F&M Installation Instructions for gasket P/Ns." The mechanic who performed the most recent maintenance before the accident stated that he replaced the copper gasket and retorqued the filter adapter but did not replace the fiber gasket. At the time of the accident, the fiber gasket was about 42 hours beyond the 300-hour replacement instruction; the airplane had accumulated 17 hours since the time of the most recent maintenance. In April 2017, Stratus Tool Technologies released a revised oil filter adapter installation manual, which contained a note stating, "the oil filter adapter transfer cylinder must be re-tightened to 65 foot pounds of torque between 8 and 12 hours of operation after installation or any time the adapter is removed and reinstalled." Another note stated, "if the oil filter adapter is loosened, or removed from the engine for any reason, it must be re-installed using new gaskets, tightened in accordance with these installation instructions and properly safety-wired." Also in April 2017, Stratus Tool Technologies issued Instructions for Continued Airworthiness, which stated that, at each oil change and each 100-hour or annual inspection, the mechanic should "inspect the oil filter adapter for oil seepage" and "if oil seepage is detected, replace the fiber and copper gaskets on the transfer cylinder with new gaskets." The instructions also stated that the "use of a torque wrench is mandatory when installing or reinstalling the filter adapter" and that the mechanic should "safety-wire the transfer cylinder to an appropriate safety-wire location on the engine accessory case"; afterward, the mechanic should "run the engine and check for oil leaks." An additional instruction stated that a mechanic should "check and verify that the body does not move (rotate around the transfer cylinder) when 10 to 20 pounds of force is applied to the body in a manner that would tend to rotate it around the transfer cylinder" and "if the body rotates around the transfer cylinder, remove the safety-wire and tighten the adapter." The instructions further stated to "always install new fiber and copper (where used) gaskets each time the filter adapter is removed and reinstalled on the engine." AIRPORT INFORMATIONThe overhauled engine was installed in the airplane in June 2003 at an airplane total time of 1,119 hours. Engine Oil Filter Adapter Design The engine was equipped with an F&M Enterprises Inc. engine oil filter adapter, model C6LC L, which was installed under Federal Aviation Administration (FAA) Supplemental Type Certificate (STC) SE09356SC. The current STC holder, Stratus Tool Technologies (owned by Aero Accessories Inc.), purchased the STC from F&M Enterprises about 5 years before the accident. The complete certification package for the STC could not be found by the FAA Aircraft Certification Office. The purpose of the adapter was to enable the engine to use a conventional spin-on oil filter. As manufactured, the oil pump was equipped with a brass oil screen mounted to the casing; the filter adapter used the oil screen bore to attach to the engine. The adapter included a tee casting (housing) and a hub (shaft), which was threaded into the oil screen hole on the engine's oil pump casting. The tee casting had a sleeve with a through-bore and a mounting base that was threaded so that a spin-on oil filter could be attached. A crown (1-inch bolt head) at the outboard end of the shaft secured the tee casting against the oil pump casing. A copper gasket was placed between the crown and the outboard surface of the sleeve's bore; a fiber gasket was placed between the oil pump casting and the inboard surface of the sleeve's bore. Oil inlet and oil outlet passages are provided through the hub and the tee casting to circulate oil from the oil screen hole to the spin-on filter and vice versa (see figure 1). Figure 1. Oil filter adapter. The adapter was originally designed to use two AN900-200 copper gaskets. At an unknown time and for an unknown reason, F&M Enterprises changed the gasket between the oil pump casting and the inboard surface of the sleeve’s bore to a fiber gasket. The fiber gasket, part no. FM07, was manufactured from 3750 Leak-Guard material produced by Garlock; the last order that F&M Enterprises placed for the gasket was in July 2013. Stratus Tool Technologies stated that, since the time that it purchased the STC, fiber gaskets have been ordered from Corley Gasket Company, which has not had any FAA oversight. According to the accident airplane owner, the oil filter adapter was likely installed on the then-newly overhauled engine in June 2003. No documents were found regarding the installation of the adapter, but the adapter was mentioned in logbook entries from March 2004 and January 2007. STC Holders' Installation Instructions According to records that Stratus Tool Technologies provided, at the time that the accident oil filter adapter was installed in May 2019, the Instructions for Continued Airworthiness for the oil filter adapter assembly (which had last been published in October 2013) stated, in part, "new gaskets are to be installed anytime the oil filter adapter assy [assembly] is removed and re-installed" and "replace gaskets at 300 hours or 3 yrs whichever occurs first." The Instructions for Continued Airworthiness further stated to "refer to F&M Installation Instructions for gasket P/Ns." The mechanic who performed the most recent maintenance before the accident stated that he replaced the copper gasket and retorqued the filter adapter but did not replace the fiber gasket. At the time of the accident, the fiber gasket was about 42 hours beyond the 300-hour replacement instruction; the airplane had accumulated 17 hours since the time of the most recent maintenance. In April 2017, Stratus Tool Technologies released a revised oil filter adapter installation manual, which contained a note stating, "the oil filter adapter transfer cylinder must be re-tightened to 65 foot pounds of torque between 8 and 12 hours of operation after installation or any time the adapter is removed and reinstalled." Another note stated, "if the oil filter adapter is loosened, or removed from the engine for any reason, it must be re-installed using new gaskets, tightened in accordance with these installation instructions and properly safety-wired." Also in April 2017, Stratus Tool Technologies issued Instructions for Continued Airworthiness, which stated that, at each oil change and each 100-hour or annual inspection, the mechanic should "inspect the oil filter adapter for oil seepage" and "if oil seepage is detected, replace the fiber and copper gaskets on the transfer cylinder with new gaskets." The instructions also stated that the "use of a torque wrench is mandatory when installing or reinstalling the filter adapter" and that the mechanic should "safety-wire the transfer cylinder to an appropriate safety-wire location on the engine accessory case"; afterward, the mechanic should "run the engine and check for oil leaks." An additional instruction stated that a mechanic should "check and verify that the body does not move (rotate around the transfer cylinder) when 10 to 20 pounds of force is applied to the body in a manner that would tend to rotate it around the transfer cylinder" and "if the body rotates around the transfer cylinder, remove the safety-wire and tighten the adapter." The instructions further stated to "always install new fiber and copper (where used) gaskets each time the filter adapter is removed and reinstalled on the engine." WRECKAGE AND IMPACT INFORMATIONA postaccident external examination of the airplane revealed that engine oil coated the belly of the airplane and that several holes appeared in the engine crankcase. The filter adapter was loose, and the adapter housing could be rotated about the shaft (see figure 2). The crown head of the shaft and the oil filter screen bolt head both remained safety wired. Oil was concentrated in the area of the adapter and adjacent firewall. The nut on the hub had several wear marks, consistent with a tool slipping on the nut. There was a zip tie around the adapter arm, which held two wires. The plastic and wear were consistent with the zip tie being installed several years earlier, and the location of the wrap end was position near the nut, prohibiting the installation and removal of the nut. Figure 2. Rotation of oil filter adapter. The fiber gasket was found protruding with its outside edge extending beyond the castings. Additionally, a tear was observed in the gasket where the adapter housing abutted the engine case. The safety wire was removed, and a torque wrench was used to determine that the breakaway torque of the adapter was 9 foot-pounds. Removal of the adapter revealed that the fiber gasket had torn (see figure 3) and contained several lips where the gasket had apparently been pinched between the engine case and the adapter housing (resulting in a crescent impression). The copper gasket was intact. Figure 3. Three views of the tear in the fiber gasket. Testing was performed on an exemplar fiber gasket to determine why the accident fiber gasket split. When the adapter hub was not fully torqued to the required 65 ft-lbs, the housing could be moved about the shaft with minimum force, and oil was observed leaking from the area where the adapter housing met the engine case while the engine was running. During some of the test installations of the oil filter adapter, when the adapter was torqued to 65 ft-lbs, the housing could be rotated about the hub when manual pressure was applied. When the adapter was properly torqued and the adapter housing was rotated by force, the rotation would result in a crescent impression in the gasket's outer material, similar to that found on the accident gasket. Less force was required to make the crescent impression if oil was present on the fiber gasket. Despite creating various imperfections on both new and used gaskets and using various installation methods and torque values, investigators were unable to duplicate the fiber gasket tear that occurred with the accident oil filter adapter. ADDITIONAL INFORMATIONA review of the National Transportation Safety Board accident and incident database as part of this investigation revealed at least six previous oil starvation events (from 2009 to 2019) involving an F&M Enterprises Inc./Stratus Tool Technologies oil filter adapter due to either the failure of the gasket or the installation of improper gaskets. In response to this accident and reports of oil leakage at the fiber gasket on some spin-on oil filter adapters, Stratus Tool Technologies issued mandatory Service Bulletin SB-001, dated October 25, 2019, which stated that the oil filter adapter should be inspected for oil leakage and gasket damage. The service bulletin provided detailed instructions of how to install the adapter properly (eliminating rotation of the housing to prevent loosening of the sleeve) and how to mark the adapter to provide a visual indication of rotation after it is installed. The service bulletin noted, “Stratus Tool Technologies has discontinued the use of fiber gaskets. Only copper gaskets are approved for initial installation or reinstallation of F&M or Stratus Tool Technologies oil filter adapters.” The FAA issued Airworthiness Directive 2022-04-04, which required operators to remove F&M or Stratus oil filter adapter fiber gaskets from service and replace them with copper gaskets. According to the FAA, the unsafe condition prompting this airworthiness directive was engine power loss due to oil starvation, which was caused by failure of the fiber gasket. The airworthiness directive became effective on March 29, 2022.
A total loss of engine power due to oil starvation as a result of the failure of an oil filter adapter fiber gasket.
Source: NTSB Aviation Accident Database
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