Engines: Feedback - Canadian Aviation Service Difficulty Reports

Transport Canada Comments:

Rolls Royce has acknowledged additional instances of potential outer combustion case cracking by issuing Revision 3 to M250-C47 CEB A-72-7002. The latest revision decreases the interval of the repetitive visual inspection for the weld size at the fuel nozzle boss. Remain vigilant when inspecting this area. Cracking and separation of the fuel nozzle boss could lead to potential power and performance reduction. Additional Alert Commercial Engine Bulletins have been released to also cover the M250-C28, -C30 & -C40 series Roll Royce engines.

Transport Canada Comments:

An engine investigation revealed that a foreign object had entered one of the cylinders and damaged the piston. This resulted in the piston cracking and allowing combustion gasses to pressurize the crankcase thereby forcing out the engine oil.

The source of the foreign object was not known however the evidence left behind on the piston indicated that it may have been caused by a piece of lockwire.

It is important for Aircraft Maintenance Engineers to be certain that the areas surrounding critical areas be cleaned of any foreign materials following maintenance activities.

Transport Canada Comments:

After conducting an investigation, it was found that Lycoming Mandatory Service Bulletin (MSB) 639 had not been performed at the recommended 50-hour interval following rocker arm replacement during overhaul. To prevent further incidents, Transport Canada Civil Aviation suggests that owners, operators, and maintainers incorporate MSB 639 and continue to file Service Difficulty Reports (SDRs) in the event of rocker arm defects.

Transport Canada Comments:

The MA-3 and MA-4 series are updraft style carburetors found on Lycoming, Continental, and other normally aspirated engines. They are currently manufactured by Mavel-Schebler Aircraft Carburetors (MSA) and were previously manufactured by Precision, Facet, and Volare.

The accelerator pump discharges fuel only when the throttle fly is moved toward the open position. In MA4-5, MA-5 and MA-6 series carburetors, this additional fuel is fed through the main discharge nozzle, and in smaller carburetors such as the MA-3 and MA-4 series, a separate discharge tube is utilized. This discharge tube is bonded in the sidewall below the venturi and main discharge nozzle.

Possible indications of a liberated discharge nozzle could include:

• Obstructed throttle fly, jammed throttle control
• Fuel found in airbox
• Cylinder Foreign Object Damage (FOD)
• Failure to start
• Sluggish acceleration during takeoff or other phases of flight

Accelerator pump discharge tubes are bonded in place during assembly or overhaul and undergo a specified torque check to determine serviceability. Transport Canada Civil Aviation (TCCA) recommends that a detailed visual inspection of this area be performed whenever possible to detect a disbonded accelerator pump discharge tube and that such defects continue to be reported by submitting a Service Difficulty Report (SDR).

Transport Canada Comments:

It was confirmed that all 3 internal wrenching screws part number (P/N) 10-349652, which secure the flange to the body of the magneto, were found loose. S-1200 series magnetos, which include 4, 6 and 8 cylinder models all use this method of attaching the flange to the body of the magneto.

Possible scenarios involving loose or fully migrated P/N 10-349652 screws include: oil leak, metal contamination of engine oil system or magneto failure.

Service Difficulty Report (SDR) data indicates this event is not a trending defect, the majority of related occurrences were prior to 1997. The inclusion of the following information in the S-1200 Series Service Support Manual may have played a role in mitigating a continuing airworthiness concern.

Multiple notes and warnings are included in the published service manual, stating to remove and discard the flange securing screws and washers, regardless of whether disassembly is for the purpose of inspection, parts replacement, or overhaul. Additionally, adherence to published fastener torque specifications is highlighted.

A daily pre-flight check may not specifically include checking for security of attachment of the magneto, although including such an item may be beneficial.

Transport Canada Comments:

The oil filter in this occurrence has experienced a filter collapse-pressure failure. This is most likely due to excessive pressure buildup during a cold start. Unfortunately, as the filter manufacturer suggests “…after the element is crushed, you’ll have little or no oil filtration. You won’t find the crushed element until the next oil change, as oil pressure will appear normal on the engine oil pressure gauge.”

Identifying signs of a filter collapse-pressure failure may be difficult, a domed filter top, an oil leak or a high revolutions per minute (RPM) during a cold start may indicate that the filter has experienced an over-pressurization. Transport Canada, Civil Aviation (TCCA) suggests that owners, operators and maintainers pay close attention and identify the root cause when defects such as these arise.

For additional information on this subject published by the oil filter manufacturer, please refer to Tempest Tech-Tip 0613 – Alaska Cold Starts

Transport Canada Comments:

Champion Aerospace has published Service Bulletin (SB) SB2-19A Mandatory inspection of impulse coupled Slick by Champion magnetos. Engines utilizing Slick 4200, 4300, 4700, 6200, 6300 and 6700 series magnetos, which have had the impulse coupling replaced with a kit dated 26 February 2015 through to 1 February 2019 are affected. Background information in the SB notes: A loose or broken rivet could potentially enter the gear train of the engine resulting in damage to the gear train or damage to engine accessories and could possibly cause catastrophic engine failure.

Transport Canada, Civil Aviation (TCCA) encourages all owners and operators to review the contents of this SB and continue to report service difficulties for any loose rivets found.

Transport Canada Comments:

The manufacturer, Lycoming, has issued Mandatory Service Bulletin 632B to identify and remove from service certain connecting rods with non-conforming small end bushings. The Federal Aviation Administration (FAA) has issued Airworthiness Directive 2017-16-11 to mandate the inspections and actions listed in the Lycoming Service Bulletin. Transport Canada urges the report of any related service difficulties found on engines not listed in the models affected section of Mandatory Service Bulletin 632B.

Transport Canada Comments:

In this event, the published instructions for continued airworthiness (ICAs), specified the use of a special tool for installing the MCDs. The operator suggests that the lack of special tool use contributed to the MCD not being secure and backing out enough to still engage the shut off valve and resulting in oil loss.

It is difficult to speculate why the maintainer did not use the tool to secure the MCDs. Time constraints and pressure to finish the inspection tasks or even tool availability may have been factors.

Transport Canada would like to remind operators and maintainers to follow manufacturers ICAs when accomplishing any task, no matter how straight forward the task may seem. In this event luckily the number one engine MCD, which was found not secure, remained in place and the aircraft landed uneventfully with one engine.

Transport Canada Comments:

Transport Canada Civil Aviation (TCCA) would like to make operators and maintainers of this engine and similar engine models aware of this event and to pay particular attention to this line when accessing or inspecting this area.

The root cause of the ruptured fuel line is still under investigation, however, as seen in the photos, the congestion of lines and hoses and the protective coating on the ruptured line would have made detection of a fuel leak very challenging at best. Luckily, a fuel leak was noticed during a walk around, the ensuing maintenance inspection located the event line, and a possible serious situation was avoided.

Please report any findings similar to this event to TCCA through the Web Service Difficulty Reporting System.

Transport Canada Comments:

Investigation revealed foreign material in the tube of the scavenge pump. Analysis revealed the material to be a paper towel. It is not known when this foreign material was introduced to the oil system.

This event was clearly a human factors issue. Transport Canada Civil Aviation (TCCA) continues to see these events occur (see feedback magazine past issues 1/2013: improper use of tooling causing in flight shutdown, 3/2014: oil filler cap left off and 4/2014: improper fuel shipping cap.)

Human factors related events like these continue to be difficult to eliminate, this is in part due to the fact that the aviation industry still relies very heavily on the professionalism and competence of front line individuals to detect and avoid these types of errors and doesn’t necessarily go the extra step to consider the associated organizational factors that may have contributed.

Implementing a formal Safety Management System (SMS) is a good place to start in order to understand organizational factors and their influence on safety. TCCA along with other Civil Aviation Authorities have worked to publish various online tools to aid the aviation industry in these areas. Some examples are:

1. TCCA’s Easy Reference Guide of Safety Management System-related Documents
2. Safety Management International Collaboration Group (SM ICG)
3. Maintenance Workload
4. Safety Culture

Although front line staff (ground handlers, Aircraft Maintenance Engineers [AME] and Pilots) can be considered the last line of defense to prevent these types of incidents, organizations should not rely on them to be the only line of defense. TCCA encourages aviation organizations to take the steps necessary to gain an understanding of the organizational factors that exist within their businesses so that they can better understand their influence on the safety outcomes of their operations.

Transport Canada Comments:

These tachometer generator drive adapter inserts are a common component on numerous engine makes and models. They mate the tachometer generator drive to the engine or gearbox to translate rotating movement into a percentage or rpm displayed on a cockpit instrument.

These inserts are often overlooked due to their location and low failure rate. In this event, the insert was cracked but continued to connect the tachometer generator drive to the accessory gearbox.

Due to the diligence and professionalism of maintenance personnel during the gearbox repair, the cracked insert was discovered and a possible event was averted. Well done to these maintainers for the effort to ensure they were releasing a serviceable product back to the customer.

Transport Canada Comments:

Certain tasks such as replacing gaskets, O rings or seals are often considered menial. Inattention to manufacturer’s instructions or standard practices when installing these components, may result in leaks that could have a detrimental result if a fuel leak ignited, or an engine shut down due to lack of lubrication or fuel starvation.

Maintainers are reminded to follow published instructions and verify the condition of these components prior to installing them. Many O rings, for example, have an expiry date or shelf life stated on the packaging, and do not assume a new part is a serviceable part.

In this case, due to this operator’s attention to detail and verification of the condition of this gasket prior to the installation, a potential oil leak was averted.

Transport Canada Civil Aviation (TCCA) requests that owners and maintainers continue to submit Service Difficulty Reports (SDRs) when defective parts, such as this gasket, are discovered.

Transport Canada Comments:

Magnesium castings are lightweight and strong, however they are susceptible to cracking due to thermal cycling during manufacture, fatigue failure from vibration, human factors if studs or bolts are over torqued, and corrosion if protective coatings wear or are not properly applied.

In this event, a meticulous inspection detected this failure preventing what may have been a serious incident or accident should the mount have failed altogether.

Transport Canada would like to highlight this event and recommend that maintainers and owners pay particular attention to this area during inspections. Transport Canada Civil Aviation (TCCA) commends the work of these maintainers for their thorough maintenance practices.

Transport Canada Comments:

Oil analysis is an effective tool that can be used by operators and maintainers to monitor the condition of an engine. It assists in the early detection of issues that a minor repair may rectify before costly components are damaged or a major engine failure occurs.

As seen in this event, oil analysis detected deterioration of the idler bearing before a catastrophic failure occurred and may have prevented an expensive repair or a serious incident from an engine shutdown.

Although oil analysis is effective at detecting accelerated wear of internal components over time, it has limited effectiveness in predicting a sudden break or fracture.

Transport Canada encourages the use of these programs by all owners and operators to enhance flight safety through the early detection of failing components.

Transport Canada Comments:

This report proves the effectiveness of good preventative maintenance and how an oil analysis program can help increase safety by preventing possible in flight emergencies and reduce operating cost by catching problems before they become catastrophic.

Transport Canada Comments:

Attention to detail is of paramount importance when conducting complex maintenance tasks such as engine assembly. Manufacturers’ recommendations must be followed (CAR 571 Standard 571.02). This is particularly important when the final assembly is hidden from view and not easily inspected.

Fortunately this resulted in a ground incident rather than an inflight emergency.

Transport Canada Comments:

The root cause of the broken air line has yet to be determined, however, fatigue and stress may have played a role in this failure. The photo shows the broken air line offset from the B nut, which may suggest a side load from installation.

Due to congestion of lines and bundles on many engines, it is sometimes difficult to have proper alignment when connecting fluid lines. A slight bend of a line to achieve contact, may induce stress and lead to a failure. Another common error is securing and torquing one end of the line before connecting the other end, instead of connecting both ends and then securing and torquing.

Transport Canada Civil Aviation (TCCA) would like to make operators and maintainers of this model and similar models aware of this event. It is also recommended that close attention be paid to this line when inspecting in this area.

Transport Canada Comments:

We have received several Service Difficulty Reports (SDRs) related to fuel leaks from a pinhole on this particular fuel pump part number. The leakage is attributed to a pinhole on the relief valve wall of the secondary housing as a result of erosion caused by the effect of cavitation over the relief valve cavity threads. These leaks may be barely detectable due to the size of the pinhole.

General Electric added inspection instructions in the component maintenance manual to check for cavitation on the secondary housing and issued Service Bulletin (SB) 73-0050 R00 identifying new spare parts for a redesigned main fuel pump with rerouted passageways.

Transport Canada Civil Aviation (TCCA) would like to make operators and maintainers of similar models aware of these events, and urges everyone to be vigilant while inspecting the fuel pump area for leaks.

Transport Canada Comments:

From viewing the MEC driveshaft threads photograph, it appears that the threads were worn or damaged. This condition may have been a factor contributing to the attaching nut backing off. The use of wrong hardware, cross threading or over torque of the securing nut, and thread strength, are a few possible causes of thread damage. Until an investigation is carried out, the root cause of this event remains undetermined.

Although the investigation is still ongoing, Transport Canada Civil Aviation (TCCA) would like to bring this event to the attention of maintainers and operators of the CF6-80C2B6 model or similar models. A verification of the MEC driveshaft condition and security when in this area, or before installation of the MEC, may prevent a similar or more serious incident.

Transport Canada Comments:

Post-maintenance functionals, leak checks, ground runs etc. are vital parts of maintenance procedures in the Instructions for Continued Airworthiness. All personnel must be thorough when performing such checks to ensure service difficulties like this one are discovered and rectified before the aircraft is released to service. “Well done” to these diligent maintainers for catching this service difficulty which may have had a potential disastrous outcome if not detected.

Transport Canada Comments:

Performing inspections and maintenance tasks in many sections of an aircraft can be challenging. The routing of lines, wire bundles and hoses in confined spaces makes it difficult to spot every area that may have rubbing or chafing.

Maintainers must be thorough when inspecting or performing tasks in these areas. Always follow the manufacturer’s Instructions for Continued Airworthiness (ICA) when routing lines or wire bundles to ensure that they are secure and that they do not interfere with each other.

Transport Canada Comments:

It is important that maintenance personnel be thorough when installing or inspecting fluid or pneumatic lines with regards to security and the potential for chafing against the airframe, a component or another line/bundle.

Congested areas are prone to such events and maintainers must pay particular attention to the routing of lines and bundles when working in such areas.

Although not the only contributor to this event, had the oil fill line not been chafed it may have been able to contain the engine oil.

Transport Canada Comments:

If an operator suspects they have received contaminated fuel, the airframe manufacturer’s instructions must be followed to help ensure safe operation of their aircraft.

Transport Canada Comments:

This unit is something that is called out for inspection in both the engine and airframe manuals however the airframe manual has lesser inspection requirements. Operators are reminded that when developing maintenance schedules, airframe and engine manufacturer requirements should both be considered. The manufacturers’ recommendations should be thought of as a minimum requirement; operator and industry experience should also be considered.

Transport Canada Comments:

The engine teardown revealed that the stage three nozzle had failed. This particular part was the subject of a GE service bulletin (SB) 72-1354 which recommends replacement with an improved unit.

While manufacturer’s SBs are not mandatory unless made so by an Airworthiness Directive, it is good practice to comply with them.

Transport Canada Comments:

It is common practice for many manufacturers to mate components together using interconnect couplings. These couplings are made from a variety of materials depending on the application. Some couplings are designed to shear if a component seizes, to limit the extent of damage to its mated component.

The root cause of these stripped splines has yet to be determined, but improper alignment during installation and material defects are possibilities. As stated in this event, the manufacturer’s Instructions for Continued Airworthiness (ICA) does bring attention to ensuring interconnect couplings are installed to prevent overspeed of the engine. However, maintainers are reminded to inspect the condition of the mating surfaces and to pay attention when installing components to ensure proper engagement.

Transport Canada Comments:

Transport Canada has received several service difficulty report submissions regarding leaking of the triple function switch. All events reported similar findings of leaks on the FMM. The leaks were typically detected during pre and post flight inspections where there was a noticeable fuel smell and visible wetness around the top of the FMM.

The subject switch is a new version and was introduced with Pratt & Whitney Canada service bulletin (SB) 28332R1 as a result of the previous triple function switches causing incorrect cockpit displays because of electrical contact contamination.

The engine type certificate holder is currently investigating these events. TCCA therefore recommends that operators and maintainers of this engine model and similar models pay particular attention to this area and report any leaks or other findings through their Web Service Difficulty Reporting System.

Transport Canada Comments:

The inner mesh screen serves as the secondary filter should the main engine oil filter element go into bypass. In this case, there was no indication that the filter had been bypassed and therefore the secondary inner mesh screen was not being used for oil filtering.

These maintainers are commended for their thorough inspection of this component and detection of the inner screen defect. Had the filter gone into bypass, contaminated oil would have been able to flow through the engine, which could have posed a significant threat to its continued safe operation.

Transport Canada would like to bring this event to the attention of maintainers and operators of this engine and similar models and to encourage reporting of any findings through their Web Service Difficulty Reporting System.

Transport Canada Comments:

TCCA received two service difficulty reports with identical problem descriptions. As can be seen in the attached photos, the metal band has worn through the clamp cushion resulting in a chafed scavenge line from metal-to-metal contact.

Like most engine compartments, this area is congested with lines, hoses, cables etc. and the event clamp seems to be secure, but the photo of the removed worn clamp clearly shows that it was moving.

While the investigation continues to determine root cause, TCCA brings this event to the attention of operators and maintainers of this or similar engine models. Take time to check this clamp and all securing hardware when inspecting in this area and report any finding through your Web Service Difficulty Reporting System.

Transport Canada Comments:

Investigation into this repeat event did not determine a root cause.

A defective seal was not ruled out but given the visual condition of the removed seal it is possible that incorrect maintenance practices may have been a factor. The installation instructions and required tooling are clearly defined in the manufacturer’s instructions for continued airworthiness (ICAs) and their proper use should not result in the type of damage found.

Although the safety implications of this event were low since it occurred on a multi engine aircraft, if this had occurred on a single engine aircraft the outcome may have been much more hazardous. Transport Canada would like to remind maintainers to follow published ICAs when performing maintenance tasks and to report any service difficulty findings.

Transport Canada Comments:

Although this event is still being investigated by the manufacturer and a root cause for the scoring has yet to be determined, some possible causes could be a damaged O ring or misalignment of the transfer tube, allowing the transfer tube to contact the bore.

Transport Canada Civil Aviation (TCCA) brings awareness of this event to operators and maintainers of similar models to check these bores prior to installation and report any findings to TCCA through their Service Difficulty Reports (SDR) reporting system.

Well done to this operator and maintainer for performing a meticulous inspection of the FMU and pump before installation.

Transport Canada Comments:

Transport Canada would like to inform maintainers and operators of PW120A and similar engine models of this event.

The investigation into the root cause continues, however, corrosion and stress along the weld seam may have been contributing factors.

Please be diligent when inspecting this area and, specifically, this line. Please report any similar findings through the Transport Canada Web Service Difficulty Reporting System.

Transport Canada Comments:

From the photos provided by the service difficulty report submitter, the thermocouple leads seem to have broken close to the thermocouple probe body where the assembly is attached to the engine case. Some discoloration on the thermocouple leads may indicate corrosion and the offset alignment of the lead to the thermocouple probe after breaking suggests stress or fatigue induced during installation.

The root cause of this event is still being investigated by the manufacturer, however, Transport Canada Civil Aviation (TCCA) would like to highlight this event for operators of PW306D engines and similar models. If performing inspections in this area or carrying out the 800-hour interval task, pay particular attention to the security and serviceability of the thermocouple harnesses and report any findings through the Web Service Difficulty Reporting System.

Transport Canada Comments:

The occurrence summary in the Transportation Safety Board (TSB) daily notification log of this event states that the maintenance personnel determined that an under-torqued fuel line fitting led to the drop in fuel pressure and subsequent engine power loss.

The fuel, oil and electrical systems of engines are normally housed in very cramped and restricted areas of most aircraft and access can be limited at best. Many “B” nuts for fluid lines may not have clearance to attach a torque wrench in a conventional way and a variety of extensions or adapters may have to be used for access. These extensions or adapters may result in an over or under torque situation. The proper torquing of these lines is vital to ensure they remain secure so maintainers are reminded to be vigilant when installing or inspecting these lines and consult manufacturer’s instructions or standard practices such as AC43.13-1B for proper torque calculations if using extensions or adapters.

This aircraft had an uneventful landing however had the fuel leak ignited, it may have been a very different outcome.

Transport Canada Comments:

Overhauled components regularly sit on storage shelves for extended periods and may not get inspected before being shipped.

The bearing surface of the gear shaft had numerous pit marks from corrosion, which may have been caused by improper preservation for storage. This corrosion was not detected until the protective cap was removed from the gear shaft assembly.

Transport Canada Civil Aviation reminds maintainers and operators to carry out receiving inspections to ensure serviceability of incoming components. Do not assume parts are serviceable because of the documentation attached. Well done to this operator who caught this issue prior to the gear shaft being installed in an accessory gearbox.

Transport Canada Comments:

Transport Canada Civil Aviation (TCCA) would like to raise awareness of this finding to operators and maintainers of the affected engine models. A manufacturing issue may result in a possible blockage of the FCU internal passage affecting fuel flow and may also result in a thin wall thickness condition that could lead to external fuel leakage.

The engine manufacturer, Pratt & Whitney Canada (P&WC), issued SB A57168 which addresses this issue. Please review the SB and component logs or check part numbers and serial numbers of the FCUs on the affected engine models and contact P&WC for disposition.

As TCCA continues to monitor this issue, please report any findings directly to P&WC or to TCCA via the Web Service Difficulty Reporting System.

Transport Canada Comments:

Woodward, the propeller governor manufacturer, issued Service Bulletin (SB) 83053-61-027 in 2012. The SB provides instructions for replacing bearings that were assembled with lightly crimped bearing retainers. Engineering analysis, conducted cooperatively by the engine, governor and bearing manufacturers, concluded that the failure was likely caused by a vigorous oscillatory motion of the two-piece, loosely crimped, bearing retainer resulting in fretting wear of the retainer assembly.

Further to their investigation into this Service Difficulty Report (SDR), Pratt & Whitney Canada continues to promote compliance with Woodward SB 83053-61-027. Transport Canada Civil Aviation (TCCA) concurs with this position and would like to highlight the value in assessing and following manufacturers’ recommendations, including those at the component or vendor level.

TCCA encourages submission of SDRs for similar events through the Web Service Difficulty Reporting System.

Transport Canada Comments:

The investigation of this event determined that the fuel pressure line had been disconnected during the removal of the nacelle lower structure. This is a deviation from the airframe manufacturer's procedures, and disconnection is not required. Following scheduled maintenance, a leak check was not performed before the power assurance check was carried out. A review of the Engine Maintenance Manual (EMM) and Airframe Maintenance Manual (AMM) found nothing wrong with the procedures for the task.

The described event perfectly shows how failure to follow manufacturers' Instructions for Continued Airworthiness (ICA) can lead to very serious situations. Not only did omitting steps lead to problems, but the additional step of disconnecting a fuel pressure line resulted in an engine fire. If a ground run had been performed post-maintenance, this event may have been prevented.

Transport Canada Civil Aviation reminds operators and maintainers to strictly adhere to ICA, perform ground runs after maintenance, and have a colleague check the work performed before closing panels or doors.

Transport Canada Comments:

An investigation by the engine manufacturer found the oil pressure warning was caused by an oil leak from the DC generator that was not seated on its mount. The root cause was determined as improper generator installation.

Generators or starters on most aircraft tend to be heavy, cumbersome to handle or install, and located in an area that is usually difficult to access and congested with lubrication and fuel lines as well as wire bundles. The securing hardware of the generator to its drive varies from basic stud mounts with nuts, to band clamps that encompass the generator and gearbox mounting flanges.

Although these different mounting systems may seem straightforward, you must follow the manufacturer’s instructions to ensure proper installation. Normally, they need to be in a certain orientation for wiring hookup, which may or may not be aided by a locator pin. Many have specific torque procedures for clamps or specific torque sequences for stud mounted, and other components may require removal to facilitate an installation.

In this event, the crew was fortunate to land without incident but had the generator detached from the mount, it may have resulted in a very different outcome. Transport Canada Civil Aviation reminds all maintainers to be diligent and follow the manufacturer’s Instructions for Continued Airworthiness (ICA) regardless of how simple the task may seem.

Transport Canada Comments:

In this event, an oil leak was found, and a seal replacement was carried out by maintenance personnel. Unfortunately, the seal failed on the next flight even though ground runs had been performed after its replacement. Further inspection found a buildup of seal material on the mating surface, which probably resulted in the sealing grooves being worn off and another oil leak.

An investigation into the root cause could not rule out the possibility of both seals being defective. However, it was determined that improper maintenance practices likely contributed to the failure of the second seal. It was found that the replacement seal was not repositioned according to the maintenance manual instructions. A third seal was installed, and the aircraft returned to service.

With the demands of meeting schedules and deadlines in a very competitive market, many tasks are at risk of being rushed to completion. In this circumstance, it appears that a full inspection of the area including mating surfaces may not have been completed prior to installation and repositioning of the propeller shaft seal. Transport Canada Civil Aviation (TCCA) reminds maintenance personnel that they have a responsibility to accomplish tasks in accordance with the appropriate standards of airworthiness and to remain vigilant for human factor issues that may impact the quality of their work.

Transport Canada Comments:

Pratt & Whitney Canada Service Bulletin (SB) 21931 is related to this issue. In summary, the calculated value for the ITT can fluctuate due to intermittent contact between the negative bus-bar support bracket bolts and the turbine support case (TSC) insulation blanket. To eliminate interference, the SB provides instructions to re-orient the negative bus-bar support bracket bolts to increase the clearance with the TSC insulation blanket. Transport Canada, Civil Aviation (TCCA) recommends compliance with this SB.

Transport Canada Comments:

Transport Canada Civil Aviation (TCCA) has received numerous Service Difficulty Reports (SDRs) related to compressor bleed valves on Pratt & Whitney Canada (P&WC) models PW305A, PW305B and PW306A engines.

The purpose of this Feedback article is to raise awareness of P&WC Service Bulletin (SB) 25401R7 and SB 24645R6. These SBs introduce a new bleed valve solenoid valve to improve the durability of the compressor bleed valve. Reference P&WC Service Information letter (SIL) PW300-198, which advises operators of these SBs.

TCCA encourages operators to follow all manufacturers' recommendations and consider implementing these SBs in the interest of safety.

Transport Canada Comments:

The importance of security and proper routing of lines, cables, bundles etc. cannot be stressed enough. With the confined areas of some aircraft, it may seem impossible to ensure that no chafing or interference of moving parts exist.

In this event, the root cause was determined as improper routing of the ignition cable. This may seem like a human factors error; however, it may have made sense to install the cable in such a way as to avoid interference with other lines or bundles. Luckily this event ended without incident; however, had the event occurred during flight, the outcome may have been much worse.

When carrying out such tasks, please follow the manufacturer’s instructions and if there are doubts or concerns about the security or proper routing, contact the manufacturer for verification. Always check clearance of moving parts when routing bundles, lines or cables to ensure no interference with controls.

Transport Canada Comments:

Many maintenance tasks involve mundane procedures that require repetitive actions. The replacement of fuel nozzles is one such task that involves the removal of old and installation of new O-rings on numerous transfer tubes, depending on the engine model.

In this event, an O-ring was found missing from a transfer tube causing a fuel leak. Fortunately, this was detected on engine start prior to flight. Had the leak occurred during flight and ignited, it may have had a much worse outcome.

Complacency caused by repetitive tasks, distraction from the job at hand, fatigue, and the pressure to get the job done are all possible factors that can lead to such events. Aircraft maintainers face significant threats to maintaining diligence when carrying out any type of work, but the threats related to repetitive activities are elevated. Being aware of possible human factor errors, and recognizing when they are most likely to affect one’s performance, are essential skills for any aircraft maintainer to master.

Transport Canada Comments:

Seals are often replaced to correct oil leaks, but the seal itself is not always the root cause. As seen in the attached photo, there are visible wear marks in the area of the seal running surface of the gear shaft. Replacing a seal in an attempt to correct an oil leak caused by a worn or damaged seal running surface often results in the leak reoccurring very shortly thereafter.

Limited access to these components often makes it difficult to inspect and verify the amount of wear on the running surface, however, using technology such as inspection cameras, or other similar devices, greatly improves the ability of the maintainer to detect such damage.

Transport Canada Comments:

Damaged O-rings and seals are a common root cause for many leaks in oil, fuel and hydraulic systems on aircraft. Many factors, such as limited access and lack of proper tooling, contribute to the possibility of damaging seals on installation. However, in this case, the fuel pump drive gear shaft appears to have been scored, reducing the effectiveness of the oil seal. In cases like this, simply replacing the seal is unlikely to be effective and the shaft would normally require repair or replacement to correct the oil leak.

Transport Canada Comments:

Carbon seals are a proven industry standard in a wide variety of aircraft and engine applications. The seals are ideal for use because of their low coefficient of friction, low wear rate, high thermal conductivity and resistance to oxidation.

Unfortunately, all of these characteristics are ineffectual if the seal is damaged. Installation without proper tooling, insufficient cleaning of sealing surfaces, seal carriers and bores etc. or inattention when installing driven components such as a starter generator are some of the factors that may cause seals to be damaged and leaks to occur.

Inspect both the seal and the seal running surfaces to ensure they are not damaged. Use recommended lubricants and cleaners where applicable and clean thoroughly and always follow manufacturer’s Instructions for Continued Airworthiness (ICA) when installing, removing, inspecting or handling these components.

Transport Canada Comments:

Events such as these are all too familiar to maintainers and operators, where a new or recently overhauled component is installed, and during testing or ground run, they are found to be defective or unserviceable.

The improperly installed bushing may have been the result of incorrect tooling, failure to follow component maintenance manuals, poor maintenance practices or may have been dislodged due to poor handling during shipping or receiving.

Transport Canada Civil Aviation would like to remind maintainers that the certification and serviceability of a component to be installed on an aeronautical product is not only the responsibility of the overhaul shop but also the person who certifies the installation. Do not assume parts bearing certification tags are indeed serviceable, carry out a thorough inspection of components prior to installation.

Transport Canada Comments:

Pratt & Whitney Canada (P&WC) is aware that cracks develop occasionally on the weld, equally in the pre- and post-mod configurations (see P&WC Service Bulletin No.3533R1) . These cracks typically do not affect the functionality of the bracket and are usually discovered during opportunistic inspections when the tubes/bracket assemblies are replaced.

Transport Canada would like to make maintainers aware of the possibility of these cracks and to pay particular attention to these transfer tubes when circumstances provide access to the FMU as well as during scheduled maintenance.

Transport Canada Comments:

During cruise, the number two engine oil pressure fluctuated between 40 and 55 psi with the oil pressure light illuminating on and off during the flight. The number two engine was feathered in accordance with the Quick Reference Handbook (QRH) and the oil pressure increased from 50 to 60 psi and was noted as 62 psi on landing. During the troubleshooting, an oil leak was found at the oil pump drain. Further inspection of the area revealed that two bolts holding the oil transfer tube retaining plate had sheared and allowed the retaining plate to vibrate and chafe through the body of the oil pump leading to a hole in the pump casing.

Investigation into the event discovered that a non-mandatory service bulletin (SB) had been issued recommending a periodic visual inspection to check for fretting of the transfer tube retaining plate and ignition support bracket, and to verify the torque on the attaching hardware.

Transport Canada encourages all operators to review SBs issued by manufacturers and recommends adopting these types of inspections as part of their maintenance programs. Although the aircraft landed uneventfully, it could have been much worse and would have likely been avoided had the SB been complied with.

Transport Canada Comments:

Transport Canada has received several similar Service Difficulty Reports (SDRs) with the Fuel Filter Impending Bypass Switch identified as the specific part causing difficulty for the illumination of the CAS message.

Pratt &Whitney Canada has published Service Bulletin (SB) SB25455 introducing a replacement switch which annunciates using a normally open contact and has an electrical inverter for interface compatibility purposes. The replacement switch alleviates the existing false annunciations due to the deterioration of the current switch’s normally closed contacts.

It is strongly advised that particular attention be given to the SB’s CAUTION statement which instructs maintainers to NOT remove the bypass valve to facilitate removing the switch.

Transport Canada Comments:

The operator confirmed that the low oil pressure event occurred on the first flight following the replacement of the scavenge oil filter. An investigation by the operator suggested that the scavenge oil filter cover packing was damaged during the installation and that environmental factors may have diminished the ability to perform an effective inspection during the leak check.

Maintainers often find themselves in situations where factors like weather conditions and accessibility create difficulties in performing certain tasks, however maintainers are reminded to take all necessary steps to perform these tasks, to be thorough when performing maintenance and follow all instructions for continued airworthiness.

Transport Canada Comments:

This type of failure can be caused by many factors such as mishandling of the line, improper alignment prior to final torqueing or excessive vibration. Maintainers must be careful when working with fluid lines to avoid dangerous situations.

Excessive vibratory loads can be more difficult to detect and diagnose. Propeller balancing is an important step in reducing vibratory loads and should be carried out in accordance with the manufacturer’s recommendations.

Another less obvious source of damaging vibratory loads can come from Starter Generator failures. Often when a Starter Generator bearing fails, it will put a massive vibratory load that can damage many engine components (including fluid lines). After such events, maintainers must use extra care in inspecting the entire engine for secondary damage.

Transport Canada Comments:

It is believed that the engine may have been repeatedly shutdown with the power lever still in the BETA range. This could cause the reversing cable to stretch and in turn allow the BETA valve to go out of rig.

Evidence of lightning strike was found that may have contributed to the rpm fluctuations (residual magnetism was found in the prop governor).

Transport Canada Comments:

It was not determined when this bracket was omitted. It is likely that it was missed during some maintenance activity such as an engine change or major inspection. Maintainers must be aware of build specifications and service bulletin status when installing an engine or when conducting maintenance. They must also ensure that the engine is in the correct configuration.

Transport Canada Comments:

This is not the first time Transport Canada has seen reports of Skydrol deteriorating seals and causing issues to other systems. Maintainers are reminded that even minor leaks must be investigated and corrected before they develop into major problems.

Transport Canada Comments:

Incompatible chemicals can potentially cause major problems for aerospace products. Issues can include corrosion, hydrogen embrittlement, and seal erosion as in the case above. Aircraft Maintenance Engineers must be aware of which products are approved for use on the equipment they maintain as listed in the most current manufacturers’ publications.

Transport Canada Comments:

Teardown findings revealed one high pressure turbine blade was missing approximately one third of its airfoil and other blades were missing material and showed hot corrosion.

Damage was consistent with what is considered harsh environment deterioration.

Maintenance tasks such as compressor washes and hot section inspections help reduce the potential for events such as the one described above. Pratt & Whitney Canada have information available to help operators determine what and when maintenance tasks should be done. Service Information Letter PW100-172R3 has information regarding harsh environment operation and can be found on Pratt & Whitney’s website: http://www.pwc.ca/en/home

Transport Canada Comments:

Operators are reminded that conducting maintenance must be done in accordance with CAR 571.02 “Maintenance and Elementary Work performance Rules” which includes the following statement: “A person who performs maintenance or elementary work on an aeronautical product shall use the most recent methods, techniques, practices, parts, materials, tools, equipment and test apparatuses that are

1. Specified for the aeronautical product in the most recent maintenance manual or instructions for continued airworthiness developed by the manufacturer of that aeronautical product.
2. equivalent to those specified by the manufacturer of that aeronautical product in the most recent maintenance manual or instructions for continued airworthiness; or
3. in accordance with recognized industry practices at the time the maintenance or elementary work is performed”

Transport Canada Comments:

Several Service Difficulty Reports (SDRs) have been received reporting “Fuel Imbalance” master caution messages during flight. Maintenance inspections found dislodged fuel check valves, which prevent backflow of fuel from wing tanks to centre tanks, as well as permit engine fuel cross-feeding when electrical boost pumps are in operation.

It was discovered that the retaining wire, which holds the check valve in its correct position, is of an insufficient diameter allowing the check valve to become dislodged and, consequently, allowing fuel to bypass the check valve.

Transport Canada Civil Aviation would like to make operators and maintainers aware of Airbus Canada Service Letter CS-SL-28-20-004, which provides instructions for the replacement and installation of an improved retaining wire part number P/N 2183023-101.

Transport Canada Comments:

Transport Canada Civil Aviation (TCCA) would like to bring this event to the attention of operators and maintainers of similar aircraft models. At this time, no root cause has been determined, however, the photo provided shows a fine spray of fuel coming from what may be a crack or corrosion pit at a fuel manifold.

With the easing of COVID-19 restrictions and the increase in flying operations, many operators are having issues related to less than optimum preservation practices. When bringing aircraft back into service, proper ground runs and inspections are vital to ensure that all the aircraft’s systems are serviceable.

This event may not actually be related to a preservation problem, but it is still a good example of what operators may experience and what they should look for. For this event, please pay particular attention to the manifold and line when inspecting in this area and also be aware that these conditions may exist when introducing an aircraft back into service.

Transport Canada Comments:

This event appears to be a “human factors” related issue and serves as a valuable reminder for maintainers to be diligent even when carrying out some of the most basic maintenance tasks. This Service Difficulty Report (SDR) highlights the importance of post maintenance procedures such as engine run ups and leak checks, verifying for correct part numbers, and adherence to instructions for O-ring lubrication prior to installation. Transport Canada supports and recommends the replacement of used O-rings after each use. Documenting and investigating events such as these through a Safety Management System (SMS) program could assist in determining a possible means of prevention in aviation organizations.

Transport Canada Comments:

Investigation into this event revealed that a loose connector tube was the cause of the leak. This event appears to be a “human factors” related issue as maintenance had been accomplished on the affected area prior to the oil loss.

A safety management system can help prevent this and other similar type events by documenting, investigating and determining possible means of prevention. This must all be done in a non-punitive fashion that can bring everyone involved together to raise awareness and promote a safety culture.

Transport Canada Comments:

There have been numerous Service Difficulty Reports (SDRs) submitted regarding the correct configuration of the forward compressor bearing housing assembly P/N 6893617 for Rolls-Royce Corporation (RRC) M250 C20, C20B and M250 B17, B17B engine models.

The original configuration used two roll pins to secure an oil seal in the bearing housing assembly, however this design lacked squareness control of the seal and caused damage.

To reduce the potential for damage, RRC issued CEB1100, which introduced a new bearing housing assembly, P/N 6893617, and provided the instructions necessary for the rework of the original bearing housing assembly, P/N 6853505. The rework included the removal of the roll pins, machining a groove on the inside diameter, and the cutting of an access slot for installation and removal of a retainer ring. Upon completion of the rework, the bearing housing assembly was to be identified as P/N 6893617.

Various revisions of the above-mentioned CEB have been issued, revision one provided rework instructions to add two retaining ring access slots to the original bearing housing assembly P/N 6853505, and to identify the reworked part as P/N 6893617. Revision three changed the rework from two slots to one slot but retained the instructions to identify the reworked part as P/N 6893617.

Since there have not been any instructions to remove either a one slot or two slot configured bearing housing assembly, both configurations are in circulation, both will be found during overhauls and both are being received from vendors as overhauled parts.

Transport Canada Civil Aviation (TCCA) would like to inform maintainers and operators that after a lengthy investigation by the Federal Aviation Administration (FAA), both configurations have been found to conform to the approved type design and are acceptable for installation.

Transport Canada Comments:

The engine manufacturer Rolls Royce published M250 Part Information Letter (PIL) 2016-008-D to introduce the release of a new part number (P/N) for the #5 annular ball bearing. This PIL is applicable to the M250 engine series and the new P/N M250-10795 bearing is interchangeable with the old P/N M250-10106 bearing. A number of service difficulty reports exist where metal chips were detected in the oil system during engine operation with the new P/N bearing installed. Operators and maintainers are encouraged to report service difficulties for M250 engines with either the new or the old P/N bearing installed.

Transport Canada Comments:

Investigation into this event involved researching the manufacturers instructions for continued airworthiness (ICAs) to ensure proper routing and securing of all lines and bundles in this area. The operator could not find any ICA that specified the routing.

This is a good example of the Swiss Cheese model in accident causes: a series of events that align and cause an event. The blocked crankcase breather along with the blocked vent tube caused pressurization of the oil system and may have resulted in an engine failure.

Operators and maintainers are reminded to be diligent when securing lines, hoses, or wire bundles in any area. ICAs may not give specific instructions so attention to proper routing to prevent potential rubbing and chafing is essential. TCCA encourages everyone to report similar finding through their Web Service difficulty Reporting System.

Transport Canada Comments:

Although the submitter of this event stated that they found reports of other Teledyne Continental engines with broken exhaust valve springs, a search of our service difficulty data base did not find any SDRs submitted with this Parts Manufacture Approval (PMA) part number.

PMA parts are eligible for installation on Canadian aircraft or on an aeronautical product intended for installation on a Canadian aircraft provided that the parts are marked in accordance with the part marking requirements set out by the FAA. The parts must be accompanied by an authorized release certificate which certifies that the parts conform to the applicable design data approved by the FAA or the Minister and indicates the aeronautical product for which they are eligible.

Transport Canada brings this event to the attention of operators and maintainers for awareness of a potential problem with these PMA parts. If you have experienced related problems with these valve springs on this engine model or similar models, we encourage reporting events through your SDR system for trend monitoring and possible continued airworthiness safety actions.

Transport Canada Comments:

Transport Canada Civil Aviation (TCCA) has received several similar Service Difficulty Reports (SDRs) which indicate broken magneto mount flanges and/or adapters as well as impulse coupling fractures.

TCCA recommends that maintainers and owners pay particular attention to the flanges and adapters while inspecting the ignition system. SLICK Service Bulletins (SB) SB1-19A and SB2-19A address reports of impulse coupling broken rivets and stop-pins liberating and potentially entering the gear train, which could contribute to seizure of a magneto. The failed magneto in this event appears to still have the pin in place but it is difficult to determine if the rivets were a factor due to the damage.

Transport Canada continues to monitor for these types of failures. Maintainers, owners, and operators of these products are encouraged to continue reporting similar events through TCCA’s Web Service Difficulty Reporting System.

Transport Canada Comments:

As explained in the problem description of this Service Difficulty Report (SDR), the Approved Maintenance Organization (AMO) followed receiving procedures, and all documentation was verified against the cylinder pack prior to installation. However, upon installation, it was discovered that one cylinder assembly was not correct, and all cylinders from the set were subsequently removed.

The tapered and parallel cylinder assemblies are very similar in appearance and therefore, it is understandable that the incorrect cylinder may have been mistakenly included with the rest of the cylinder set in a moment of inattention.

Further investigation found that the subject cylinder was incorrectly labeled during packaging at the manufacturer’s location and then shipped, and consequently, the packaging procedure is being reviewed.

Transport Canada Civil Aviation (TCCA) would like to bring this event to the attention of all maintainers and operators. The importance of product certification and verification of eligibility in accordance with the Canadian Aviation Regulation (CAR) 571 during receiving or installation cannot be overstated. Always confirm part and serial numbers of the components and never assume packaging labels are correct. TCCA commends the AMO for the professionalism shown in this event since this cylinder could have inadvertently been installed if it had not been for the attention of the maintainer prior to installation.

Transport Canada Comments:

This is a familiar occurrence for many operators receiving aeronautical products from overhaul. The expectation is that overhauled components are serviceable and ready to be installed with minimal maintenance required to return to service.

The root cause of the missing spacer may have been due to inattention during assembly, unclear or confusing procedures in the Instructions for Continued Airworthiness (ICA), poor quality assurance practices or inadequate training programs to name a few.

Fortunately, the good maintenance practices of this service facility, during the incoming ground run-up and visual inspection, detected the leak and may have prevented what could have been an engine fire and possible loss of life or loss of the aircraft.

Transport Canada Civil Aviation (TCCA) commends the proactive procedures of these maintainers and encourages that such actions be taken by all operators and maintenance personnel.

Transport Canada Comments:

Without further investigation such as a lab analysis, it would be difficult to determine the root cause of these sheared rocker cover studs. Unless corrosion is present or some kind of impact damage is evident, a visual inspection usually does not reveal any findings.

We normally attribute these events to metal fatigue and eventual failure. A manufacturing quality escape, a defective or improperly installed stud or heli-coil as well as poor maintenance practices such as not verifying proper torque for the stud installation may also be contributors, which could result in a serious occurrence such as inflight shutdown and emergency landing.

Transport Canada Civil Aviation (TCCA) would like to make operators and maintainers aware of this event and urge everyone to pay particular attention when working in these areas, and to look for similar problems. Please report any such occurrence by submitting a Service Difficulty Report (SDR).

Transport Canada Comments:

Although the sump screen performed as intended and prevented metal from entering the oil system, it may have been much worse had the nut backed off the connecting rod. Maintainers must be thorough when performing maintenance and adhere to Canadian Aviation Regulations (CARs), Instructions for Continued Airworthiness (ICAs) or standard industry practices (AC43-13-1B) as applicable. The cause of this cotter pin’s failure was not identified, however repetitive use, improper size or incorrect installation procedures are known contributing factors to broken cotter pins. Never reuse cotter pins and ensure you have the proper size for the application by verifying the correct part number from the Illustrated Parts Catalog (IPC).

Transport Canada Comments:

Continental Motors has released Service Bulletin SB17-06 that deals with this issue. It can be found at the following URL:

http://www.continentalmotors.aero/support/service-bulletins.aspx

Transport Canada Comments:

Although it is not known exactly when the cotter pin was incorrectly installed or perhaps omitted, Transport Canada Civil Aviation would like to remind maintainers to be vigilant when conducting work.

Aircraft Maintenance Engineers, non licensed technicians and apprentices are all capable of having a ‘bad day’ and miss a step in an assembly procedure or incorrectly install a component. There are rules in place to help minimize these risks such as those listed in Canadian Aviation Regulation (CAR); 573.08, 576.06 and 576.07. In addition to the above regulations, maintainers must also have at their disposal any relevant technical data related to the task(s) they are to perform. This includes manufacturers’ instructions for continued airworthiness (ICA’s) and standard practice information. (For example: correct cotter pin installation can be found in U.S. advisory circular 43.13-1B and in the Aviation Maintenance Technician Handbook.) Maintainers must also keep in mind CAR 571, Standard 571.02 which states in part: “Persons who perform maintenance or elementary work are required to follow the manufacturer’s recommendations, or equivalent practices. Where the recommendations of the aircraft manufacturer are incompatible with those of the engine, propeller, or appliance manufacturer, the recommendations of the aircraft manufacturer shall be used. Where the manufacturer has not made specific recommendations, standard industry practices are to be used.”

Transport Canada Comments:

It is unusual that the magneto was functioning normally when this discrepancy was discovered. This example illustrates the need for regular inspections and follow up action when an unusual finding is discovered.

Transport Canada Comments:

Transport Canada was informed that this cylinder is affected by FAA Airworthiness Directive (AD) 2016-16-12 and was scheduled to be complied with within the prescribed time frame. Operators are reminded that it is important to inform their local airworthiness authorities of such events so that the effective dates of ADs can be evaluated and if necessary be amended.

Transport Canada Comments:

Safran Helicopter Engines conducted an investigation of the engine chip event, and found that the debris came from the front bearing of the fuel pump drive intermediate gear. The front bearing has a metal “stamped” separating cage. The root cause of the engine chips was revealed to be fragments of metal coming from the “stamped” separating cage. Safran has since published Service Bulletin (SB) 319 75 4090 to introduce a modification to the front bearing. The modification is a change to the design of the bearing separating cage, from “stamped” to “riveted machined”. Transport Canada, Civil Aviation (TCCA) recommends that operators and maintainers of the Arrius 2R model engine review SB 319 75 4090, and consider incorporating this modification for increased reliability of the engine.

Transport Canada Comments:

Transport Canada is bringing attention of this event to operators and maintainers of the Williams FJ44-3A and similar models.

The photos attached show the extent of several failed components of the power turbine temperature sensor system. The electrical connector plug P20 may have disconnected because of the damaged threaded bezel fracturing therefore not being secured to the receptacle J20, however why it fractured could be the result of the sensor itself which appears to have overheated and distorted its shape. This distortion may also have caused the mounting bolt and grommet to pull out of the mounting bracket.

TC would like to remind operators and maintainers to pay particular attention to this sensor and connector when inspecting in this area and note of any findings by reporting them through their SDR reporting system.

Transport Canada Comments:

With the vast assortment of monitoring and indicating systems on aircraft engines, an electrical harness may contain numerous electrical connectors of different applications and sizes. As well, these connectors have multiple fastening features, from the standard threaded connector, to quick disconnect bayonet connectors, to name a few.

In this event, the arcing of the contact in the connector may have been caused by an internal failure, or damage to the connector sealing grommets, or a foreign object shorting between contacts, or shorting by corrosion from moisture ingress, as examples. From the photos provided, it appears that the keyways are serviceable, which would rule out misalignment of the connection.

Commonly, the repair and maintenance of electrical connectors is carried out in accordance with either the manufacturer’s principle Instructions for Continued Airworthiness (ICA) or Advisory Circular (AC) 43-13, which provide a wide range of standard practices. Transport Canada would also like to highlight that many manufacturers now publish specific electrical standard practice procedure manuals for their products. These procedures have useful information specific to connector care, as well as recommended products used to protect from moisture or other liquids when environmental protection is needed. When performing tasks on or around electrical wiring or hardware, remember to consult the manufacturer’s specific connector care publications, if provided.