Fixed Wing - Make D to Z: Feedback - Canadian Aviation Service Difficulty Reports

Transport Canada Comments:

Most of the time, it’s impossible to detect if fluid lines are deteriorating. These fuel lines are on-condition, however, they should still be carefully inspected during inspections.

Transport Canada Comments:

When inspecting hydraulic lines, make sure that areas that are tight, or areas where lines may come in contact with other lines or structure, are protected from chafing.

Transport Canada Comments:

A reminder when inspecting cables, ensure the entire section of the cable including areas that are hard to see are inspected properly. Keep in mind that the control cable has to last safely until the area is inspected again and in this case there was an expectation for this cable to last 2500 hours before re-inspection.

Transport Canada Comments:

Recently, a number of different aircraft models have reported broken main wheel tie bolts. Always deflate the tire before removing a wheel since broken tie bolts can cause the rim to separate and has been known to seriously hurt the person working on the wheel. In this case the tire had deflated on its own but that is not always the case.

Transport Canada Comments:

It is unknown what caused the feeder cables to short and burn the firewall, however, these images show the kind of damage that can be caused by large cables shorting and burning. On high current cables, sometimes the damage is already done by the time the protection devices trip and the power to the affected circuit is cut. Loose connections on these cables can cause overheating of the terminal blocks and should be checked for proper torque during inspections.

Transport Canada Comments:

An in-flight shutdown and damage to the parts was caused by improper maintenance. It is important that maintenance personnel follow instructions published by the manufacturer and take time to inspect the work. There is no evidence that this incident was caused by human factors, however it reminds us that the person doing the work could be distracted, fatigued or pressured to get the work done.

Transport Canada Civil Aviation (TCCA) recommends having someone inspect your work before close up in order to minimize the risk of faulty workmanship.

Transport Canada Comments:

The operator inspected other aircraft in the fleet and found the identical cannon plug corroded on the left and right side wing root of other aircraft. These cannon plugs are covered by heat shrink, which by orientation of the wiring harness, is letting humidity penetrate the wiring harness. Trapped humidity seems to be the cause of the corrosion.

In order to reduce the number of recurring defects, operators should adjust their maintenance schedules when they find issues that may be caused by the environment they operate in.

Transport Canada Comments:

Due to high starter-generator loads, operators should consider adjusting appropriate component overhaul intervals based on reliability data to prevent failures between overhaul intervals.

Transport Canada Comments:

Proper inspection techniques should be able to identify these worn parts during scheduled inspections before they fail in service. Access to the area where these parts are located requires a man lift or a work stand because the aircraft has a T-tail and makes it harder for maintenance staff to work in the area. Availability of proper equipment is important to ensure that the inspection tasks can be properly completed.

Transport Canada Comments:

Upon further inspection, both mounting hole ears have fractured. DA20-A1 and DA20-C1 share a similar design, although this failure mode has not been reported in the past. It is important to recognize that higher time aircraft may require special attention to areas that undergo stress on a regular basis, particularly flight control systems. Owners, operators and maintainers are reminded to submit a Service Difficulty Report if any similar defects are found.

Transport Canada Comments:

The root cause of this failure is not entirely clear. Incorrect torque during the installation of the control horn bolt, and/or horizontal stabilizer water drain hole obstruction in combination with freeze/thaw cycles may have contributed to this failure. Maintainers are reminded to refer to the appropriate fastener installation torque values. In cases where specific torque values are not defined, standard torque values should be referenced.

Transport Canada Comments:

Incorrect installation of worm drive clamps in the induction system can lead to engine power loss. Owners, operators and maintainers are reminded to be aware of the most current instructions for continued airworthiness (ICA) available for their specific product.

Service Information Letter SI 40NG-007 dated 10 May 2011 was issued by Diamond Aircraft Industries GmbH informing customers on the installation of worm drive clamps. The information in this letter has since been incorporated into the DA 40 NG’s maintenance manual. See document number 6.02.15 Revision 3, section 20-70-00.

Temporary Revision AMM-TR-MÄM 40-901 dated 9 November 2017 was issued and includes the following:

“Worm drive clamps are for single use only. Replace clamp with a new clamp every time the clamp is loosened or removed. Secure each worm drive clamp with safety wire once they are installed and tightened to the appropriate torque (see Paragraph D. Tightening Torques for Worm Drive Clamps).

Caution: Reuse of worm drive clamps can lead to a failure of the clamps and may cause loss of engine power.”

Transport Canada Comments:

This incident occurred during flight with an engine failure. Unfortunately, the error wasn’t discovered during post-maintenance ground runs.

It is possible to mix up the fuel supply line and return fuel line connections on both left-hand and right-hand wing root connection points, although the part numbers are unique. This is also possible on DA 40 D and DA 40 NG model aeroplanes.  Transport Canada Civil Aviation reminds maintenance personnel of the importance of labeling hoses / fittings during disassembly.

Transport Canada Comments:

The quick reaction and persistent approach the flight attendant took in this case prevented what could have been a very different outcome. It can sometimes be difficult to pinpoint the source of electrical fires/smoke like in this case. Often, electrical components are buried behind sidewalls or under floor. During routine maintenance, a thorough inspection of these components could prevent inflight emergencies.

Transport Canada Comments:

Had it not been for an attentive pilot performing the usual pre-flight walk around or an eager AME performing the same old 150-hour inspection, these snag may have gone unnoticed. Remember the dirty dozen and avoid complacency.

“Today is the day I will find something!”

Transport Canada Comments:

This interesting event shows how a component can fail for many reasons. Control valves will typically fail mechanically or electrically. The backing out of a set screw shows a possible assembly error at overhaul or manufacture.

Maintainers and operators are asked to watch for even the less apparent faults.

Transport Canada Comments:

Cooling turbine bearing failure often results in seizure, and multiple service difficulty reports (SDRs) suggest that this is accompanied by smoke/oil mist in the cabin. Other indications of failure have been described as: smoky haze, white smoke, or acrid smell in the cabin/cockpit. Cabin temperature rising, while not responding to temperature controller or manual temperature control, has also been reported.

It is important to reiterate that inspection and servicing outlined by the manufacturer should be completed correctly and during the suggested interval. In addition, SDR data suggests that high oil level, or a blockage in the air delivery system may contribute to cooling turbine failure.

Australian Transport Safety Bureau (ATSB) covered a similar occurrence: AB-2018-033. The following picture from this report illustrates the result of a typical cooling turbine bearing failure.

Transport Canada Comments:

Additional reports of failure have been discovered after experiencing ECS anomalies in flight. Low airflow to the cockpit, inability to maintain selected heat settings and reports of cabin pressurization loss have been described by flight crews.

Learjet has noted that adequate cabin pressurization is available regardless of a rupture in the muffler assembly. It may cause the cabin air not to be routed through the operator’s desired duct locations, but it will still reach the cabin, and with additional ECS ducting through the bulkhead, safe cabin pressure levels will be maintained.

This area is routinely accessed during a 300 hour hydraulic filter replacement. Damaged or loose outer insulation wrapping around the muffler or insulation material located near the hydraulic manifold is a good indication that the cockpit ECS muffler may be cracked.

Transport Canada Comments:

Loss of hydraulic fluid can lead to complete hydraulic failure. Main and Auxiliary Hydraulic systems share the same reservoir, loss of fluid may render both unserviceable. As well, cavitation can damage hydraulic pumps which can be very costly. Learjet Service Bulletin (SB) 45-29-17 was issued in 2010 and is currently at revision 2. The SB subject matter recommends replacing low pressure switches in the main, auxiliary and spoiler systems. Transport Canada Civil Aviation (TCCA) recommends that operators follow the manufacturer’s recommended Service Bulletins.

Transport Canada Comments:

The cause of the arcing damage is not currently known. The damage is quite significant and is in an inspectable area, therefore TCCA would like to highlight this service difficulty report to promote industry awareness.

Transport Canada Comments:

As highlighted in previous Feedback articles, this area of the passenger door is prone to water ingress and corrosion which can lead to cracked and broken bolts. In this case, along with broken bolts the operator found cracks in the door fittings.

These, as well as previously reported corrosion and bolt breakage events have been assessed by the design approval holder and determined to pose minimal safety risk provided the recommended inspections and standard aircraft maintenance practices are respected. The area is the subject of a lengthy inspection interval and the maintenance instructions do not require the removal of the bolts to inspect for corrosion. Aircraft operated in roles where the door stairs are used frequently in harsh environments may wish to consider preventively replacing the bolts during the inspection to provide additional reliability and prevent in-service failures and their associated operational delays.

Transport Canada Comments:

After consultation with the service difficulty report (SDR) submitter, Transport Canada Civil Aviation (TCCA) understood that the area was inspected in accordance with Service Bulletin (SB) 80-0444. No other occurrences have been reported to TCCA. Operators and maintainers of these aircraft are reminded, that whenever performing maintenance in this area, to remain vigilant and observant for this reported condition. If the condition of loose jam nuts is found, please submit an SDR accordingly.

Transport Canada Comments:

This Feedback Article aims to raise awareness in the PC 12 community of potential undetected corrosion being present under specific bushings of the yoke fitting assembly. It is suspected that this corrosion weakens the bore in the yoke fitting which can cause the separation of the lug from the rest of the yoke assembly. This specific aircraft was positioning for takeoff at the end of the runway when the lower trailing link broke away. The gear assembly is presently with Pilatus in a Swiss lab for investigation.

Pilatus specifies in their MLG Component Maintenance Manual (CMM) that up to “25,000 flying hours or 30,000 landings (whichever comes first), the overhaul of the MLG is done 'on condition' and requires the disassembly, cleaning, check, repair (if necessary) and assembly of the component”. The overhaul consists of an examination and dimensional check of the bushings, but removal is optional.

Transport Canada Civil Aviation recommends that operators pay extra attention to these bushings during all routine maintenance checks for signs of corrosion. The Pilatus MLG CMM provides specific instructions for the subject bushings' removal, inspection, repair and reinstallation.

Transport Canada Comments:

The SRM repair mentioned by the submitter is Rudder Upper Hinge Fitting Repair RM06299 (Installation of an aluminum bushing). This repair has the operator increasing the top bolt hole to a larger size to accommodate a bushing, adding strength and preventing play-inducing wear.

Pilatus offers another repair, Rudder Upper Hinge Attachment Repair RM05387 (Replacement of the nutplate with a self-locking nut and washer). This repair replaces the anchor nut with a self-locking nut and washer. This repair also adds an inspection panel to access the lower portion of rudder rib 6.

Play in the rudder attachment fittings is checked while performing Pilatus Task: Rudder Inspection Check - 12-B-55-40-00-00A-313A-A. Operators are asked to keep this defect discovery in mind when finding play in the rudder upper hinge fittings of PC-12 aircraft.

Transport Canada Comments:

The operator provided the following additional information:

A hole was found in the L/H wing fuel line part number (P/N) 528.24.12.173A caused by a chafing wire from the belly beacon P/N L78B18/l79A18N, which chafed through the insulation, exposing the bare wire, and had arced on the fuel line, causing the leak. The wire was able to chafe due to a rotated Adel clamp and standoff, which held the two beacon wires.

The aircraft was defuelled, the fuel line was removed, the wire was repaired with Raychem in accordance with standard practices, silicon fusion tape was applied to the hydraulic line, which the Adel clamp was attached to, and the Adel clamp was attached/reinstalled on the tape and positioned away from all lines. The Adel clamp cannot rotate due to friction from silicon tape. A new fuel line P/N 528.24.12.173B was then installed in accordance with standard practices.

The aircraft was refuelled, and the line was pressure tested with the boost pump. The engine run was completed; no further faults were found, and the aircraft returned to service.

This operator was fortunate that this difficulty did not progress into something much worse. A fleet campaign was initiated to inspect for proper clamp and wire position to ensure for necessary clearance between the two wires and fuel lines. No further findings were reported.

Clearance must be maintained between wires and adjacent components and structures. Please be vigilant for these types of dormant failures.

Transport Canada Comments:

The flight crew of this aircraft was fortunate that the bellcrank failed during taxi and not in the air. Inspection by maintenance found that the bellcrank did not appear over-stressed or bent. The aft flange of the cracked portion seemed to have distorted as the bellcrank was in the final stage of failing. Black residue in the area of the forward cracked pieces was also noted.

After removal, the failed bellcrank was sent to Pilatus headquarters in Stans Switzerland for failure analysis. Preliminary findings point to a very small corrosion spot as the starting point of the crack/fracture.

The subject aircraft at 29 959 hours air time is of particular importance as it has been running on an airframe life extension program since nearly 10 000 hours air time.

At this time, Transport Canada does not recommend operators modify their maintenance schedule as the investigation by Pilatus is ongoing.

Transport Canada Comments:

The crew of this aircraft was fortunate that the component bolt failed on the ground and not while in-flight.  Pilatus has no lubrication schedule set for this bolt but has set a 600hr inspection interval for the steering components.

This submission is an excellent example of a Service Difficulty Report (SDR).  
From the Canadian Aviation Regulations (CARs)  Part 1, Subsection 1, Interpretation 101.01:

Service difficulty means a failure or malfunction of, or defect in, an aeronautical product;
Reportable service difficulty means a service difficulty that affects or that, if not corrected, is likely to affect the safety of an aircraft, its occupants or any other person

Please consult the CARs Part 5 Division IX for reporting requirements and timelines.  You may also reference Advisory Circular (AC) 521-009 available as a link on Web Service Difficulty Reporting System (WSDRS).  The AC is an excellent tool for guidance on SDR submission.

Transport Canada Comments:

This special inspection proved its worth. Sometimes routine maintenance can seem mundane and uninteresting. This particular maintenance staff was able to find the exact issue the inspection was calling out. Following procedure and being attentive during inspections can save a crew from an inflight failure.

Transport Canada Comments:

This is a good reminder about landing gear electrical components and the effects that our Canadian climate can impose on them. Extra care should be taken when inspecting this area of the aircraft. If necessary, remove heat shrink and coverings to get a closer look.

Transport Canada Comments:

The temperatures on the ground at the time of this event would have been above freezing. No mention was made if the aircraft had been washed or if it had been left out in the rain. Water will turn to ice as aircraft climb into colder temperatures at altitude. Care must always be exercised to ensure that aircraft systems such as aileron controls are not left wet prior to flight. In this situation, water had made its way into the bell crank bearing; it could have been external water or condensation that built up over time.

Many manufacturers use sealed bearing assemblies with no prescribed lubrication interval. Depending on the aircraft’s operating environment, operators should be aware that they may need to go over and above what the manufacturer recommends. The use of manufacturer approved moisture displacing lubricants is a great way to prevent this type of occurrence. (Maintainers must always use only manufacturers’ recommended products as listed in the approved publications)

Transport Canada Comments:

TCCA has recently received information about a similar incident involving another Piper PA 30 aircraft, wherein the landing gear collapsed, resulting in significant damage to the aircraft. Positive gear retraction/extension can be problematic when push-pull (conduit) cable function has been degraded, or otherwise described as stiff. The cable assembly is an integral part of the normal extension/retraction and emergency gear extension system. Degraded function of this cable may negatively affect any emergency gear extension.

Warning signs that may indicate a stiff push-pull cable include:

• Circuit breaker trip during operation;
• High electrical load;
• Gear extends slowly, especially in cold weather;
• Gear motor unusually warm/electrical odour present.

FAA published AD 77-13-21 related to Piper Service Letter (SL) 782A, and Special Airworthiness Information Bulletin (SAIB) CE-08-50 which promotes the importance of SL 782B. TCCA discussed this topic in Feedback issue 2010/3 without noting the related FAA AD. Owners, operators and maintenance personnel should pay particular attention to the published recommended maintenance practices and subject matter of SAIB CE-08-50, and continue to complete the reoccurring requirements of AD 77-13-21.

Transport Canada Comments:

Piper Aircraft published service letter (SL) 1263 due to MLG piston tube fatigue cracking. Shortly thereafter, an accident (National Transport Safety Board report WPR21LA117) involving the separation of a R/H MLG occurred. The root cause was identified as failure of the landing gear strut piston tube due to fatigue cracking from corrosion pitting.

It was noted in a subsequent Service Difficulty Report (SDR) 20210806009, that Piper has produced a replacement strut assembly, part number (P/N) 67037-006 (also referenced in the above SL), which appears to have a notable design improvement in the affected area of the lower fork.

Transport Canada Civil Aviation (TCCA) recommends compliance with SL 1263. Additionally, paying special attention to the area of the fork identified in this SDR is also recommended. High cycle aircraft, such as those used in a flight training role, may be particularly susceptible.

Transport Canada Comments:

Owners, operators, and maintainers are reminded to always follow the appropriate instructions for continued airworthiness (ICA). In cases where clarity of assembly cannot be positively ascertained, the type certificate holder should be contacted for assistance.

Although the outcome of this occurrence was likely burdensome on many levels, it was not catastrophic. Service Difficulty Reports (SDRs) should continue to be submitted for occurrences related to assembly / installation lack of clarity. The potential for mistakes and resultant consequences are not always apparent while completing complex tasks, especially if these tasks are new to the Aircraft Maintenance Engineer.

Transport Canada Comments:

The engine power loss occurred during flight in the right-hand engine when the pilot selected the inboard fuel tank, as the outboard fuel tank capacity had been exhausted. An emergency was declared with the intention to land as soon as possible. While troubleshooting, the electric boost pump was turned on with no effect. The pilot utilized the fuel cross-feed system from the left-hand engine, which provided fuel supply and returned the right-hand engine power back to normal. The aircraft landed safely shortly thereafter.

The Federal Aviation Administration (FAA), the State of Design for the product, published Airworthiness Directive (AD) 80-18-10, which requires inspection of all fuel selector valve control cables using 10x power magnification each 100 hours. Piper Service Bulletin No. 507 has been referenced within the AD for specific inspection locations, highlighting all swivel fittings.

Although the fuel selector valve control cable had been recently inspected prior to the incident, the defect was not uncovered at that time. The fuel selector valve control cable inner wire fractured under the crimping cup of the swivel fitting.

It is important to remain vigilant and avoid complacency when completing all maintenance, with special attention to the requirements of an AD.

Transport Canada Comments:

The Service Difficulty Report (SDR) submitter is correct, Piper SB 1131A and SB 1179 both focus on the upper torque link attachment point. For Piper PA-28 and PA-32 series aircraft that operate in a flight-training role, experiencing hard landings, or where many takeoff and landing operations are performed routinely, it is recommended to pay special attention to the lower stub axle lug as a possible failure point.

A cracked stub axle lug may be partially hidden from view by the inner wheel half when installed. The use of a 10x power magnifying glass, as described in Chapter 32 of the Maintenance Manual, to visually inspect the radii may assist in identifying a cracked stub axle lug. Transport Canada Civil Aviation (TCCA) encourages owners, operators, and maintainers to continue reporting any defects noted.

Transport Canada Comments:

The occurrence aircraft had undergone maintenance just prior to the incident flight. It was determined that the emergency exit window assembly was not installed correctly, possibly due to a lack of clarity of the instructions in the maintenance manual (MM).

In addition to the above occurrence, there could be a link to an accident in 2019 where the emergency exit window assembly could not be opened. It was impossible to determine the exact cause of this failure, as the assembly was completely destroyed by the post-impact fire.

Link to Transportation Safety Board of Canada (TSB) Air transportation safety investigation report A19Q0091

“A post-impact fire broke out. Given that the fire was burning near the right wing, on the side where the main door was located, the pilot and the passenger-instructor went to the back of the aircraft with the intention of opening the emergency exit window on the left side, but they could not get it open. They were still able to evacuate the aircraft through this window because the plexiglass had been shattered on impact.”

Piper Aircraft completed a thorough review of the MM instructions relevant to the emergency exit window assembly used on the PA-23-250 model. The applicable MM, part number (P/N) 753-564 has been revised, dated 31 July 2021. This latest revision provides clear, detailed instructions for the removal and installation of the emergency exit window assembly.

Transport Canada Civil Aviation (TCCA) strongly suggests owners, operators and maintainers review and adopt the latest publication of Piper Aztec MM P/N 753-564.