Aircraft did not start off with tires, or even wheels, for that matter. The Wright Flyer did not use landing gear. Instead, the launching rail system consisted of four 15-foot two-by-fours totaling 60 feet.

“[In 1909] Goodyear developed the first pneumatic aircraft tire, which replaced the runners and bicycle tires on pioneer airplanes like the Wright Flyer,” the company said.

It wasn’t until 1983 that Goodyear made the first radial tire approved by the FAA.

Specifications

The OEMs specify the specific tire size, ply rating, and pressure requirements for each individual aircraft. These elements directly impact the taxi parameters and landing operation.

During tire changes, it is crucial to install only approved aircraft tires.

Several tools assist in selecting the appropriate aircraft tire for your specific application.

Goodyear Aviation Tires features an online application guide where you can look up tires by size, part number, or aircraft.

The Goodyear Aviation Data Book contains seven sections to assist you in navigating the aircraft tire space. This booklet presents specific data on the proper tire sizes for different aircraft main and auxiliary/nose gears, speed ratings, nominal inflation pressures, dimensions, and other data users need to obtain the maximum service from their aircraft tires.

Automotive company Michelin also produces a line of aircraft tires under its Aviator brand. It also has a line of downloads to assist in outfitting your aircraft with the proper tire. 

One way an aircraft component, such as a tire, gains approval is through a supplemental type certificate (STC) issued by the FAA.  Michelin’s General Aviation STC, for example, may be found here.

All parts installed on certificated aircraft must carry some form of approval. Some approvals, such as parts manufacturer approval (PMA) parts, designated engineering representative (DER) repairs, and STCs, are alternate means of approval, which means the OEM does not support them.

Hazards

Aircraft tires are at a greater risk of damage due to their exposure to the elements, extreme temperature fluctuations, and high friction operation.

Common defects include:

• Wear: Uneven or excessive tread wear indicates that your tires may be improperly inflated.
• Sidewall damage: Cracking or bulging in the sidewalls can result from underinflation or harsh environmental conditions.
• Flat spots: Occurs due to heavy braking during landings.
• Foreign object damage (FOD): Debris on the runway can puncture or damage tires.
•  Neglect: Failure to maintain aircraft invites Murphy to hang out on your flight line.

Be wary of extreme air pressure loss. Goodyear urges the following: “Any tire removed due to a pressure loss condition should be returned to an authorized repair facility or re-treader, along with a description of the removal reason.”

Maintenance

Aircraft tires play a crucial role in aircraft operation. 

“Inflation pressure is the most important thing for the tire’s life,” said Tim Wong, service leader at VSE Aviation. “Check tire pressure before the first flight every day.”

Also important are ply ratings.

“Ply rating relates to how much load the tire can withstand,” Wong said. “The higher the ply rating, the heavier the load. Also, ply rating is a ‘rating,’ not necessarily the number of layers in a tire.”

Retreads can also be a good value, according to Wong.

“If you’ve flown commercially, 90 percent of commercial aircraft fly on retreads,” he said. “You will benefit from the OEM casing and longevity of our rubber. It’s definitely a great value with no risk.”

Tire pressure is the single most impactful maintenance item for aircraft tires, according to Philip Weber, former vice president of sales for Bridgestone Aircraft Tire.

The OEMs design aircraft tires to lose pressure as they fly, on average 2-3 percent per landing, to vent gasses that build up between the rubber layers. Regular tire pressure monitoring and maintenance will ensure proper performance and maximize safety.

Sidewall deflection is the biggest determining factor of aircraft tire longevity. The more sidewall deflection, the more quickly the tire wears, and the casing becomes scrap. Higher ply ratings give the tire more sidewall stability, resulting in more carrying additional weight. In addition, some tires have layers of Kevlar to improve tire puncture and FOD protection.

Retreads perform as well, and often better, than the original new tire. Unlike semitruck tires, where the new tread is simply welded to the outer surface of the casing, aircraft tires go through a complete re-baking process every time they are retreaded. This process makes the retread tire like new again.

Additionally, the baking process stiffens and seats the tire bead, which creates tires that are often easier to install and pressurize. In some cases (Boeing 737NG as an example), a retreaded tire can have a deeper tread than the original tire, providing longer on-wing life.

The post Understanding Aircraft Tires appeared first on FLYING Magazine.

Are service documents mandatory? No. Are they a good idea to implement? It depends, but for the most part, yes, and you’ll soon discover why.

Corrosion comes in all shapes and sizes. It is a natural process in which metals deteriorate due to chemical reactions with environmental elements, such as oxygen, moisture, and pollutants. In aviation, corrosion can manifest in various forms, including surface, pitting, intergranular, and stress corrosion cracking.

Each type poses significant risks, potentially weakening the structural integrity of the aircraft and leading to safety hazards. We’ve recently seen how corrosion affects wing spars like with the Piper PA-28 and Cessna 177 and 210, for example. These started as Service Bulletins (SBs) to inspect for corrosion and escalated to mandatory compliance in the form of Airworthiness Directives (ADs).

• READ MORE: How Do I File a Pilot Weather Report Online?

The implications are severe. Corrosion can lead to structural failures, increased maintenance costs, and, in worst-case scenarios, catastrophic accidents. Once you have the basics and understand the theory, you are ready to progress to the next level.

That’s right, it’s aircraft maintenance time, and here’s one example.

Learjet 45

The Learjet is legendary among corporate aircraft—produced from 1964 to its unfortunate scuttling in 2021. Learjet became synonymous with business aircraft in the early days of private business travel.

“Learjet models are known for their exceptional performance, speed, and range,” said Sky Aircraft Maintenance. “Airframe issues can be a common maintenance concern for Learjet aircraft. Due to the high speeds and stresses placed on the airframe during flight, wear and tear can occur over time, leading to a need for structural repairs. This can include corrosion.”

On July 13, 2007, the Australian Civil Aviation Authority released AWB 57-004 Lear Jet Industries 45 Wing Corrosion. The agency said this correspondence was needed because “recent reports have been submitted indicating that corrosion has been found on the lower skin of both wings fitted to the Lear 45 aircraft. This corrosion resulted in the replacement of the entire lower-wing skins.”

Years later, in February 2019, Learjet, now owned by Bombardier, released a series of Service Bulletins addressing “wing spar inspection.” The reason? Corrosion had been observed on the lower-wing splice plates, requiring a more frequent interval to detect and correct protective coatings.

Remember our chat earlier about adhering to the manufacturer’s recommendations? 

• READ MORE: What Does It Take to Transition From a Jet to a Piston Airplane?

Fast-forward a bit and the series of Learjet bulletins are now the FAA’s AD 2021-23-08.

What prompted this escalation? According to the AD, exfoliating corrosion was found on a particular Lear 45 upper surface of the lower center-wing, midspar splice plate during unrelated maintenance. The corrosion appeared to extend halfway through the thickness of the splice plate. Since the initial report, the FAA has received 23 additional accounts of corrosion from Learjet.

Jerel Bristol, owner of SEAL Aviation in Hollywood, Florida, was not surprised when the call came in. Bristol is aware of the trouble that Learjets have with wing-spar corrosion and knows the AD well. His team deploys to aircraft or ​AOG situations for mobile fuel leak repair, nondestructive testing, and structural repairs anywhere in the world.

During the center-wing inspection, a SEAL technician identified corrosion on the center-wing splice plate. I spoke with Bristol, and he said that it is a common area to find corrosion past repairable limits, which requires the replacement of the forward and aft splice plates.

After pulling the affected parts off the airframe, the SEAL team quickly repaired the area and replaced the damaged parts. The pictures reveal a sea of cleco fasteners. 

The guys buttoned up the Lear, and the owner was wheels-up again. 

The Cause

The big question remains: What causes corrosion?

One follower commented on a SEAL Aviation webpage post about the Lear 45 repair, stating that brine used for deicing could have contributed to the corrosion. He is not far off. Environmental elements can contribute to aircraft corrosion.

These factors include:

• Humidity and moisture, particularly in coastal regions.

• Temperature fluctuations which can cause condensation.

• Exposure to deicing fluids and other chemicals.

• Poor maintenance practices and infrequent inspections.

The environment is not the only player in the corrosion game. According to Aviation Devices and Electronic Components (Av-DEC) in its article “Causes of Corrosion,” industrial pollutants are equally harmful and can be difficult to protect against.

These include several contaminants such as:

• Ozone (exposure from high altitude, motors, and welding)

• Carbon compounds (exposure from combustion engine exhaust)

• Sulfur dioxide (exposure from engine exhaust, smokestacks, and acid rain)

Operators and GA aircraft owners alike are well advised to take heed when an SB shows up in the mailbox. A recommended inspection, especially when it can be coordinated with other scheduled or unscheduled maintenance, may help ultimately reduce the total cost of ownership and down time if/when an issue becomes an AD.

Perhaps the best reason to take a closer look is personal safety and peace of mind through identifying a problem before it manifests in something tragic.

This column first appeared in the September Issue 950 of the FLYING print edition.

The post Corrosion 101: What Causes It? appeared first on FLYING Magazine.

That statement is precisely what one does not wish to hear when test-running an aircraft following a maintenance event. The situation worsens when the aircraft is a $109 million F-35A Lightning II fighter. In January, Stars and Stripes reported that on March 15, 2023, “a hand-held flashlight left inside an F-35 engine by maintainers at Luke Air Force Base last year caused $4 million in damage.” It seems that after using a flashlight to inspect the poorly lit intake of the F-35, the maintainer failed to clear the tool before test-running the engine.

During the post accident investigation, investigators found a flashlight missing from one toolbox. The 56th Fighter Wing aircraft suffered an excess of $4 million in damage to the engine. Thankfully, no one was injured in the accident, but the engine could not be repaired locally.

This is a classic and all-too-common case of foreign object damage (FOD).

This Is FOD

FOD can be categorized as foreign object damage or debris based on the context one is referencing. FOD is a broad term that applies to just about anything. The FAA defines in Advisory Circular (AC) 150/5210-24 Airport Foreign Object Debris (FOD) Management that FOD is “any object, live or not, located in an inappropriate location in the airport environment that can injure the airport or air carrier personnel and damage aircraft.”

FAA AC No. 150/5380-5B Debris Hazards at Civil Airports addresses FOD and the ramifications of such. One key highlight states that “foreign objects on airport pavements can be readily ingested by aircraft engines, resulting in engine failure.” The FAA lists several possible FOD objects, many of which you will instantly identify as commonplace in aircraft operations. In section B of the AC, the FAA calls out “aircraft and engine fasteners (nuts, bolts, washers, safety wire, etc.); mechanics’ tools; flight line metal (nails, personnel badges, pens, pencils, etc.); stones and sand; paving materials; pieces of wood; plastic and polyethylene materials; paper products; and ice formations in operational areas.” 

FOD-Related Accidents

Just how bad is the FOD problem? One might say that the issue is an epidemic. The FAA devotes quite a bit of attention to it, and rightly so. FOD is hazardous and can negatively impact operations.

The FAA website cites the Current Airport Inspection Practices Regarding FOD (foreign object debris/damage) report, stating that FOD exists in many forms, comes from many sources, and can be found anywhere in an airport’s air operations area (AOA). The report explains how damaging FOD can be to aircraft, puncturing tires, punching holes in airframes, and nicking turbine blades or propellers. And in extreme cases, engine failure. Damage is not isolated to just aircraft or equipment. Airport employees are also susceptible to FOD-related injuries. Errant bolts or other foreign objects on the ramp could be propelled by prop wash, jet engine blasts, or helicopter rotors, turning them into mini-missiles.

• READ MORE: Breaking Down Sudden Stoppage Inspections

The report states that FOD costs the U.S. aviation industry $474 million annually. The global aviation industry’s losses are an estimated $1.26 billion annually. These totals include direct and indirect costs, such as flight delays. The FAA is asking for airports, airlines, and the general aviation community’s assistance in documenting the occurrence of FOD and submitting data to the FAA FOD database.

Despite all the awareness campaigns and actions taking place, FOD is still a significant problem that may be growing. A recent Air Force Times article states that “foreign object debris was one factor that led the number of ground accidents to nearly double from 11 in 2022 to 21 in 2023.” If anything, rates of occurrence are headed in the opposite direction. In March, USA Today reported that United Flight 1118, a Boeing 737 taking off from Houston’s George Bush Intercontinental Airport (KIAH) ingested bubble wrap into the engine, causing a midair fire. Thankfully, the incident did not result in injury.

Unfortunately, the losses are not solely in physical damage. One of the more infamous FOD-induced incidents did not fare so well. On July 25, 2000, Air France Flight 4590 departed Paris Charles de Gaulle Airport (LFPG). Prior to rotation, Concorde struck a piece of metal with its right front tire, causing it to explode and rupture the integral fuel tank. Fuel leaking from the ruptured tank ignited, creating a loss of thrust in engines 1 and 2. The aircraft lifted off momentarily but crashed into a hotel, killing all nine crew, 100 passengers, and four people on the ground. 

The Bureau Enquêtes-Accidents (BEA) report identified the FOD as a Continental Airlines DC-10 thrust reverser door wear strip that had fallen off after maintenance. 

FOD awareness and prevention deserves our attention. These examples and others illustrate that there is seemingly no end to stories of FOD causing significant property damage and loss of life, including one instance of a self-inflicted fatal FOD accident. Columbia STS-107 was lost and its space shuttle crew perished upon reentering the atmosphere while returning from a mission. According to NASA, a loose insulation panel dislodged and damaged the carbon heat shield material on the orbiter’s left wing, eventually causing the craft to succumb to the extreme heat of reentry.

FOD can come from a variety of sources, and not all incidents are the result of negligence—nature can be equally culpable. Most people are familiar with the story of Captain Chesley “Sully” Sullenberger and the “Miracle on the Hudson.” On January 15, 2009, US Airways Flight 1549 departed New York’s LaGuardia Airport (KLGA) bound for North Carolina’s Charlotte Douglas International Airport (KCLT). Approximately six minutes into the flight, the Airbus 320-214 ingested a flock of Canada geese, disabling both engines. Thankfully, Sullenburger’s skill saved the lives of all souls on board by safely ditching in the Hudson River. 

Even smaller flying objects can cause huge problems. Andrew Warwick and Blake Love recently reported to KJWN in Nashville, Tennessee, for a service call. A Challenger 350 experienced a dual-engine, nonstart condition. They arrived to find the APU inlet packed with dead cicadas. It appears that cicadas are drawn to the APU’s warmth and noise. Operators in heavy cicada areas like this are advised to run their APUs sparingly and check for FOD frequently.

FOD Prevention

To begin a FOD prevention program, start with the following:

• Identifying causes.

• Establishing an FOD awareness program.

• Establishing a maintenance program.

The AC mentioned earlier then breaks down each of the above actions with detailed guidelines to help one succeed in the fight against FOD.

• READ MORE: 5 Things You Can Do to Help Prevent Foreign Object Debris

Another resource the FAA makes available is its Foreign Object Debris Program. The website (faa.gov/airports/airport_safety/fod) reveals several tools, resources, and technical publications for managing a successful FOD program.

Marcela White, co-owner of Tavaero Jet Charter, knows FOD is serious business. When asked who was responsible for FOD risk mitigation at Tavaero, White’s simple response was—everyone.

“Pilots, mechanics, and airplane cleaners are all trained to check for any FOD damage on the airframe or in the engines,” White said. “Pilots are the last line of defense and perform their preflights with a sharp eye. Anything beyond obvious visual damage gets escalated to the maintenance department. The job is not over after the flight either. The pilots go back through everything during post-flight inspections. Crewmembers follow an extensive checklist that includes servicing the aircraft fluids, cleaning the windows and windshields to ensure no chips are found, checking oxygen levels, and checking the airframe and engine blades for FOD.”

I met John Franklin, the head of safety promotion at the European Union Aviation Safety Agency (EASA), during the T-C-Alliance online coffee chats early in 2020. I asked Franklin about his legacy of fighting FOD.

“In terms of FOD, it’s where I started my safety career, as the U.K. Defense FOD Prevention Officer, or the ‘Fodfather’ as it was called at the time,” he said with a smile.

Franklin broke down the steps EASA is taking to raise FOD awareness. 

“From our side, we are trying to promote the topic wherever the opportunity arises,” he said. 

“Every year, the EASA team participates in the annual FOD Walk at our local airport at Dusseldorf [Germany]. This provides a great opportunity to promote the importance of active FOD prevention. After the FOD Walk last year, we published an article on our Air Ops Community website [easa.europa.eu/community/topics/fod-prevention].”

Even with all EASA’s efforts, more work remains, especially with regard to getting the word out. 

“We also promote FOD, particularly when we have other promotional events and webinars on maintenance safety and airport ground handling,” Franklin said. “From our analysis, these certainly seem to be the communities that have the largest role in stopping FOD from causing a safety issue to an aircraft. Additionally, we promote the topic of clean cockpits to airlines having had some occurrences with FOD jamming flight controls or causing other problems to avionics.”

Much like a 12-step program, Franklin recognizes that awareness of the FOD problem is only the first step. One must put in parameters to stop FOD at the source.

“It’s also important to have a FOD analysis program to further identify the sources of FOD, so you can manage them at the source,” he said. “There is no point just continually cleaning away FOD without thinking where it is coming from and how to stop it.”

How the Experts Stop FOD 

FOD control begins with attention to detail, tool control, and housekeeping. There are solutions designed with this in mind. FODS LLC, located in Centennial, Colorado, provides FODS mats to prevent any material from entering the airfield by clearing the tire treads before entering the airport. They recently completed a project at Terminal 5 at Chicago O’Hare International Airport (KORD).

I asked some of the top names in the industry to help me map out strategies to deal with FOD. James Logue, the director of maintenance at Latitude 33 Aviation in Carlsbad, California, told me how his team approached the FOD issue, and provided a new perspective.

“It’s important to think about FOD proactively,” Logue said. “Think about an object and its placement in terms of how it might become FOD. I’ve seen large water bottles in a galley cabinet leak out, causing water to get under the floor and into the belly, then freezing in flight, causing a fuel valve cable to become jammed. Consider what can happen if an item breaks, spills, moves in flight, where it might migrate to, what holes it could fall in, etc.”

Despite best efforts, FOD will eventually find its way to the airport. But once you identify an object as FOD, how do you dispose of it? 

Foreign Object Debris is a company specializing in FOD receptacles. According to its website (foreignobjectdebris.com), the firm “educates the community about FOD in hopes of helping to save a loss of money and potentially lives.” If you visit the site, check out its series of FOD blogs.

Jon Byrd, executive director of aviation and TCSG state aviation program adviser for Georgia Northwestern Technical College (GNTC) in Rome, contracts with Shark-Co Manufacturing to build custom foam molds that incorporate the minimum tool list and fit them into the student’s toolbox. This could have helped out the F-35 maintainer with the missing flashlight.

Speaking of tooling, Snap-on now sells a line of FOD prevention tools. I recently read about its quarter-inch Drive Dual 80 Technology Standard Handle Foreign Object Damage Ratchet design online and how it helps to prevent FOD in sensitive work environments. The cover plate and reverse lever are permanently affixed to the ratchet head with rivets to prevent debris from small parts. The tool meets FOD and foreign material exclusion (FME) program conformance.

Duncan Aviation is the world’s largest privately owned business jet service provider. I recently met with the team and inquired about Duncan’s FOD efforts. Darwin Godemann, the team leader of the Technical Education Center, offered the following insights: FOD can be anything—a wrench, pen, eyeglasses, or even rocks and stones, and i originate in many ways—objects falling out of pockets, a wayward tool, dirt and debris, or a pilot spilling their coffee.

FOD does pose a significant threat to aircraft, one that can cost the operator tens of thousands of dollars and compromise the safety of the aircraft and its function. For example, debris can result in improper stress and wear on a wire, causing an electrical fire. Coffee spilled six months ago can drip into nooks and crannies and cause corrosion. A tool left where it shouldn’t be can shift and jam a flight control. Debris from an airfield can be sucked into an engine.

Here are some examples of Duncan Aviation’s program:

• Tool control policies require shadowboxing all toolboxes and the end-of-work inventorying of tools

• Regular FOD awareness and training with a clean-as you-go policy. If you see something, pick it up.

• Double-inspection systems. Before it puts a panel back on or closes an area of the aircraft opened for work, a second set of eyes checks it out. In addition to a QA check, this ensures there is nothing in there that doesn’t belong.

• Awareness campaigns companywide. The line department tugs have magnets under them that pick up magnetic objects as they drive on the ramp.

Here are Duncan’s best practices implemented to develop an MRO FOD program:

• General housekeeping: A clean-as-you-go mentality is the most important first step in FOD prevention.

• Effective tool control system: Account for all tooling regularly and at the end of a job. Inventory lists or tool shadowing make this task much easier.

• OK to close inspection: Inspecting all areas where maintenance was performed to ensure nothing unwanted is left behind.

FOD control is potentially everyone’s problem, so it’s also everyone’s responsibility. Safety is mission critical in aviation. Failure to control FOD could be deadly.

This feature first appeared in the July/August Issue 949 of the FLYING print edition.

The post Fight Against FOD Never Ends appeared first on FLYING Magazine.

While Delta provided few details about the explosion, which is under investigation, here is what we know. Mechanics removed the tire from a Boeing 757 and transferred the wheel and tire assembly to the wheel and brake shop. I walked past that shop hundreds of times during my stint at TechOps, and to think about a tragedy of this magnitude is quite surreal.

• READ MORE: Two Killed in Delta Aircraft Tire Explosion

“It is a little bit alarming because this stuff doesn’t happen every day or every week or even every month,” Kyle Bailey, a former FAA safety expert and aviation analyst, told Atlanta Fox affiliate WAGA-TV. “These things explode, these things malfunction, people make mistakes. But sadly, in this case, two people were killed.”

I can attest that I have been an A&P mechanic for over 30 years, and 99 percent of things go off without a hitch. Unfortunately, when things go wrong in aircraft maintenance, they go terribly wrong.

Keep Your Head on a Swivel

In navigating the dangers of aircraft maintenance, it’s critical to maintain situational awareness, or “keep your head on a swivel,” according to the National Aviation Academy.

When my father worked for United Beechcraft at Fulton County Executive Airport/Charlie Brown Field (KFTY) in the early 1990s, a mechanic called for help holding a breaker bar so he could break down a King Air wheel and tire assembly. Having neglected to deflate the tire, it exploded, resulting in the death of a helper. 

Deflation is a vital step in changing a tire, according to a tip sheet compiled by industry professionals and circulated by the FAA. 

“Remove the air from the tire,” it says. “Warning: The tire will be deflated even though the size will not change. Deflate first to avoid any hazards. This is to be accomplished before the wheel is removed from the aircraft.

California Department of Public Health’s Occupational Health Branch case report 19CA002 offers some insight into what happens if technicians attempt maintenance on an inflated aircraft tire:

A stationary engineer working at an airport died when the tire and wheel he was disassembling exploded. The employees on the previous shift removed the tire and wheel from an airport passenger boarding bridge and placed it in the airport maintenance shop. The victim and a co-worker were removing the nuts and bolts that held the wheel together when the tire and wheel assembly exploded, striking the victim in the head and neck. The valve stem was not removed from the tube within the tire to release the air pressure.

The CA/FACE investigator determined that to prevent similar future incidents, employers with workers who change multi-piece tires should:

●      Implement policies and procedures as part of a safety program to ensure that tires are deflated before wheel disassembly.

●      Remove all pneumatic tires and replace them with solid rubber tires.

●      Consider providing employees with certified commercial tire service (CTS) training or hiring companies with CTS technicians.

The FAA-H-8083-31B Aviation Maintenance Technician Handbook—Airframe offers this caution: “Deflate the tire before starting the procedure of removing the wheel assembly from the aircraft. Wheel assemblies have been known to explode while removing the axle nut, especially when dealing with high-pressure, high-performance tires.”

Shop Safety Considerations

The No. 1 reason accidents happen is the failure to follow procedures, according to John Goglia, an airline mechanic and former National Transportation Safety Board (NTSB) member.

“The best way to prepare an aircraft maintenance team is through structured training,” Goglia said. “On-the-job training is one thing, but what if the guys in the shop have been doing it wrong for years? For example, aircraft tires are a lot easier to roll when inflated, even though they are supposed to be deflated when removed from the aircraft.

“Another thing to consider is that in some instances, mechanics work outside their skill, perhaps on loan from another department due to a surge in workload. Those are particularly at risk.”

In my maintenance days, the entire facility went on lockdown for training if we suffered an incident. We called it a safety stand-down, and nothing happened until we completed the task. 

Human factors, such as stress or complacency, directly contribute to many aviation accidents, the FAA said in its Aviation Maintenance Technician Handbook.

Admittedly, we do not precisely know what happened last week at the Delta TechOp shop. AMTs share a common bond and generally look out for each other.

Accidents happen, and sometimes with tragic consequences. We are duty-bound to understand what went wrong so we can correct it for future generations.

The post Deadly Tire Explosion at Delta Facility Highlights Risks in Aviation Maintenance appeared first on FLYING Magazine.

When this occurs, owners are hit with a double whammy: They cannot fly their airplanes, and the work will cost them money. Now, some might come away from the down time with a shiny new Garmin gadget or a candy pearl, glossy paint job. And those lucky enough to accomplish engine maintenance may feel a little bump in the throttle, but it is a small consolation prize.

Prepping for Aircraft Maintenance

How do you plan for maintenance?

Last year we followed a local owner-operator as he maintained his 1966 Cessna 172 Skyhawk, detailing how cost, time, and scope factored into his maintenance planning.

Under the scope, consider the point complexity. If someone is putting their plane down for an extended period of time, wouldn’t it make sense to maximize the maintenance and knock out multiple upgrades at one time? For example, if the engine is going out for overhaul, should one also do the propeller? 

Downtime is downtime. Why not combine evolutions? Cost factors into that, but with mandated limits set forth by the original equipment manufacturer (OEMs), it could make sense to just comply now rather than later. Time remains constant, and scope and cost increase, but that saves time later down the line.

There is a common misconception that negotiating an aircraft maintenance evolution is like an episode of Pawn Stars. It is not, or it is not supposed to be. 

Initial Quote

Years ago, I won a sudden-stoppage inspection bid because I was more than $3,000 higher than every other bidder.

When I took the call and gathered the information, I inquired about the serial number of the engine. When the caller recited the number, I learned it ended with an “E,” indicating roller tappet bodies, which are mandatory for Lycoming after a prop strike. I was the only one who mentioned that and, therefore, kept the customer from an expensive surprise during the inspection.

JD Kuti of Pinnacle Aircraft Engines takes a similar approach when quoting engine overhauls.

“We front load the quote as much as possible,” Kuti said. “I do not like to ask the customer for more money during a build, so we lay out the worst-case scenario during the initial discussion.”

According to Kuti, some key points include:

• A new camshaft and tappet bodies on every engine overhaul.
• Full OEM factory new to start. Once the engine is in house the team will explore parts manufacturer approval (PMA), designated engineering representative (DER), and used serviceable material (USM) options, and pass those savings along to the client.
• Supply chain constraints. Right now, manufacturing is struggling to keep up with surging demand. Have you seen the lead time for the factory-new cylinders?

A tougher conversation on the front end makes for smoother sailing later.

Closing the Deal

Once the parts arrive at the MRO, the fun is just beginning. It is inspection time.

To Kevin Allen of Aircraft Accessories International (AAI), this is the best part of repair quoting.

“At AAI we like to be upfront and transparent with the customer,” Allen said. “I will break down the different practices and try my best to educate the customer.”

According to AAI, the process of quoting landing gear overhaul work falls into one of two categories, standard work and above and beyond.

Standard Rate

For landing gear, AAI quotes standard rate inspection that includes all the necessary labor and parts to disassemble, clean, inspect, reassemble, and test.

Once the landing gear is inspected, there may be items that are considered “above and beyond” standard overhaul.

‘Above and Beyond’

Items that may be considered “above and beyond” standard overhaul include:

• Corroded parts such as piston tubes and trunnions;

• Bent, broken, or missing parts; 
• Parts that require replacement due to airworthiness directives or service bulletins. 

AAI’s price breakdown, according to the company, provides customers “price-saving options of being able to choose between DER repairs, PMA, or OEM parts.”

Keeping Everything Straight

Aircraft maintenance software company EBIS assists MROs in keeping their ducks in a row.

“Historically, we see MROs using some combination of spreadsheets, Word documents, and historical invoices to build a quote,” said Chris Heine, senior manager of customer and partner experience at EBIS. “For years, it’s been the fastest and simplest way they knew how to build a high-level quote and get it to the customer ASAP. You’re going to send out a quote that isn’t very accurate for the sake of speed. That doesn’t always lead to a great customer experience down the road.”

There is a better way, Heine said.

“MRO software and automation can help centralize data, run complex calculations in real time and quickly generate pre-formatted quotes,” he said. “For example, one can leverage software to build quotes for recurring events [i.e. annual inspections] with all the labor hour estimates, parts markup calculations and customer-specific billing rates in about 30 seconds.”

Jets MRO in Dallas shares the EBIS work order dashboards with its customers during the quote building process and throughout the entire maintenance event. Its lead technicians serve as both sales engineers and project managers, which allows them to inform customers about project status, actuals versus estimates, and any changes to the original quote.

The same automation that underpins streamlined quoting is also what solves most MRO challenges around generating invoices and collecting payments. 

The post Quoting MRO Work appeared first on FLYING Magazine.

Like everything else in aircraft maintenance, it depends. 

The truth is something can be FAA approved and still not recognized or authorized by the aircraft’s OEM. Often, owners and maintainers will use alternate means of compliance to achieve airworthiness. These solutions include, but are not limited to, a parts manufacturer’s approval (PMA), designated engineering representative (DER) repairs, and STCs.

• READ MORE: Cirrus Service Advisory Throws Fuel on G100UL Maintenance Debate

GAMI applied, and the FAA awarded STC approval for G100UL. Its unleaded gasoline is an alternative to 100LL avgas. An STC, although legal, still raises questions for some. 

What Is an STC?

The FAA issues an STC to approve a significant change or modification to an airframe, engine, or propeller operating with a current type certificate.

The FAA defines it as follows: “A supplemental type certificate (STC) is a type certificate (TC) issued when an applicant has received FAA approval to modify an aeronautical product from its original design. The STC, which incorporates by reference the related TC, approves not only the modification but also how that modification affects the original design.”

For complex design modifications, the Aircraft Certification Office may ask that you follow the Original Design Approval Process.

When Is an STC needed?

One needs an STC to make a major change to the airplane, such as installing new technology, changing the engine, or updating the interior. One must ensure that these changes meet safety standards.

An STC is required in these instances:

• Avionics upgrades, such as adding updated navigation or communication systems
• Engine conversions, such as switching to a different engine for better performance or efficiency
• Interior refurbishments, such as modifying seating arrangements or adding new features

When an applicant embarks on the STC path, they must adhere to strict criteria outlined in the FAA’s Application to Issuance process. The 17-step process ensures only the best viable solutions obtain STC approval. Ultimately, the FAA states that an STC will be issued only if:

• Pertinent technical data have been examined and found satisfactory
• All necessary tests and compliance inspections have been completed
• Alteration has been found to conform with the technical data

Great, but what does that mean?

It means that someone decided to alter the OEM design, thereby changing how the aircraft performs, introducing a new technology, or changing its mission. STCs come in all shapes and sizes, and most fly undetected under the radar.

However, in the case of G100UL, this issue is front-row center of the headlines. Why? Because in the aviation aftermarket, change is scary.

Importance of an STC

Longtime readers  will know that we stick to the book at Maintaining Your Airplane. You will note I did not mention the OEM.

Although essential, there are other means of airworthiness compliance. It all starts with documentation: logbooks, flight records, and FAA forms. The STC documents the alterations made to the aircraft, which is essential for safety and compliance.

The STC accomplishes three main objectives:

• Standardization: Ensures that modifications meet FAA safety standards
• Airworthiness: Keeps your aircraft legally safe to operate
• Documentation: Provides a formal record of the approved alterations

Be wary of individuals who perform any work but fail to document it. Paperwork is the easiest part of maintenance—you don’t even have to get dirty. Some mechanics may fight me on that, but my concern is, if they skimp on that, what other shortcuts will they take?

STCs in the Field

There is a misconception that only third-party entities develop STCs for the aftermarket. This is not true. Times change and often aircraft are modified to adapt to that change.

For example, many Boeing 747 jumbo jets have been retired from passenger flying, but some have a new mission in cargo. Boeing has an STC to convert passenger 747 airliners into cargo carriers.

Would it surprise you that Boeing and its affiliates/partners have 159 STCs recorded in the FAA STC database? Airplane manufacturers sometimes need to update their type-certificated aircraft, and in some instances, the STC route is the most efficient.

Of course, most of the STCs available in the aftermarket are from third parties. 

Duncan Aviation is the world’s largest privately owned business jet service provider. It also has a well-stocked STC library, which is searchable on its portal. The website went live in 2019, and within the first three weeks, the company had 20 STC requests for quotes.

One solution currently making STC headlines is Starlink.

In March, AeroMech announced the issuance of an STC for Starlink on King Air 200/300 Series aircraft. It did not stop there, and Wednesday announced an STC for Citation 560XL Series aircraft.

As STCs are aircraft-specific, each model adding Starlink requires a new STC.

The post What to Know About Supplemental Type Certificates appeared first on FLYING Magazine.

The issue of what is legal (in FAA terms) and approved (by manufacturers) puts maintainers in a sticky situation. On one hand, the FAA issues a supplemental type certificate (STC) allowing for products to deploy on aircraft, but the engine and/or aircraft manufacturer may not approve or recognize the STC as something permitted for use under the terms of their warranty. 

Whether an aircraft owner or operator chooses to use the alternate fuel or not is a matter of choice. The fuel has been approved by the FAA and is perfectly legal to use in the SR series aircraft. The dilemma for the maintainer arises upon returning a Cirrus aircraft to service even for something as routine as an oil change. 

• READ MORE: Identifying Corrosion in All Its Forms

Consider this scenario. The pilot opted to refuel with G100UL or the aircraft arrived with G100UL in the tank. This alternate fuel is a drop-in replacement, so 100UL could have been added to 100LL already in the tank. Granted the maintenance action in this case did not involve fuel, but the maintainer is signing for the entire aircraft to be returned to service. If they sign the repair IAW OEM guidelines, this includes Service Advisories (including one that prohibits the use of G100UL fuel). Consequently if the aircraft is carrying G100UL, then this could be an issue because the aircraft is not being returned to service IAW this Cirrus SB.

Of course, as with any guideline, the issue of signing for an aircraft is subject to interpretation. I know mechanics that will only work on aircraft they have personal history with and do not want to return to service an inherited unrecognized maintenance action.

In the advisory (SA24-14) “Transition to Unleaded Fuel and Use of Non-Cirrus Approved Fuel in SR Series Aircraft” released June 18, Cirrus said it was committed to the industry’s transition to unleaded fuels, which is underscored by its collaboration with stakeholders such as the Aircraft Owners and Pilots Association (AOPA), General Aviation Manufacturers Association (GAMA), FAA, and Eliminate Aviation Gasoline Lead Emissions (EAGLE) industry initiative.

Aircraft and engine manufacturer’s are extremely risk averse. They historically do not recognize alternate methods of airworthiness, and this includes STCs, parts manufacturer approval (PMA) parts, and designated engineering representative (DER) repairs.

There is a commercial element to this since any aftermarket PMA part procured from a third party is a revenue lost for the OEM. It appears the reason for the SB in this specific case is Cirrus’ concern about the breakdown of a fuel tank sealant that was seen in an isolated (one) aircraft known to have been fueled with G100UL.

The company will need to vet this against other aircraft in the fleet to ascertain if the perceived breakdown is an isolated outlier related to the drop-in fuel, or if the dislodged fuel tank sealant was a manufacturing defect unrelated to the use of G100UL. 

• READ MORE: 5 Attributes of a Top-Notch Maintenance Provider

“While some aspects of the initial Cirrus testing of the GAMI G100UL fuel are encouraging, other areas, including materials compatibility, remain inconclusive,” the advisory said. “At this time, Cirrus does not approve the use of GAMI G100UL fuel in Cirrus SR Series airplanes. Per Continental and Lycoming, only approved fuels may be used for an engine to be covered by warranty.” 

According to the FAA, G100UL is safe to use, hence the STC approval. This took years of testing to clear the milestones. In fact GAMI uses the fuel in its company SR22..

According to GAMI, the fuel has undergone substantial testing and displayed no issues on other aircraft. The company also disputes Cirrus’ claim that using G100UL voids the warranties on engines supplied by Lycoming and Continental, however, the engine manufacturers have confirmed its use could affect warranty claims, according to AVweb. 

Tim Roehl, president of GAMI, indicated that his team is drafting a formal response to Cirrus Service Advisory SA24-14 to be posted on its website. Roehl also said that the sealant Cirrus references is not the polysulfide sealant more commonly used in the industry but a polythioether sealant. Roehl stated that G100UL has been in service since 2010 on one wing of the company’s Cirrus SR22, using the same polythioether sealant Cirrus uses, with zero incidents.

The FAA does not comment on specific OEM warranty policies but the agency has reiterated that GAMI’s G100UL does have the STC approval. This is not uncommon as the FAA routinely approves alternate solutions without the buy-in from OEMs. The burden is on the third-party solution provider to prove airworthiness—i.e. STC holder, PMA manufacturer, or designated engineering representative for DER repairs.

What This Means for Maintainers

This fuel issue places aircraft maintenance professionals in a bit of a quandary. On one side, you have the FAA approval for G100UL, but at least one aircraft manufacturer, Cirrus, and one engine manufacturer, say they are not approved via service advisories.

The FAA typically steers clear of airframe/powerplant OEM issues until they become an airworthiness directive (AD). To assist in clearing any confusion, the agency issues periodic documents to help owner/operator/maintainer stay abreast of the situation. One such publication is the FAASTeam service bulletins.

When asked if service bulletins are mandatory, the FAA says: It depends. 

Here is a quick agency ruling: “If you are operating your aircraft under 14 CFR part 91, a service bulletin is advisory, and compliance is not mandatory unless it is included in an Airworthiness Directive.”

Another resource is FAA Advisory Circular AC 20-114, which addresses manufacturers’ service documents: “Service documents should be neither treated nor represented as the official FAA approval documents, unless either a letter of design approval from the FAA or a record that compliance has been determined by an FAA designee is on file for recommended actions indicated as FAA-approved in service documents.”

That said, service documents are beneficial and transmit a wealth of knowledge. When returning aircraft to service, it is critical to list if the action is in accordance with OEM information or another alternate form of maintenance. This comes into play when installing PMA parts, or an STC like G100UL.

The post Cirrus Service Advisory Throws Fuel on G100UL Maintenance Debate appeared first on FLYING Magazine.

As aircraft progressed, so did the enemy. Corrosion identification, prevention, and treatment is an ongoing battle.

• READ MORE: An Introduction to Aircraft Inspections

According to an EAA Sport Aviation article that makes a clear distinction about corrosion on wooden aircraft: “Lest you think corrosion is something that only happens to metal, wood can also develop a sort of organic rust. Known as dry rot, this fungus is caused by too much moisture content and can render wood unusable.” 

Corrosion will look slightly different in wooden ribs, spars, and longerons.

When it comes to inspecting structural wood, late vintage aircraft restorer Ron Alexander, who wrote about managing, flying, and maintaining aircraft for Experimental Aircraft Association’s (EAA) Vintage Aircraft Association, said there is a lengthy list of items to check.

According to Alexander, some of the things to look for include:

• Signs of mildew, which occurs due to excessive humidity and heat and potentially leads to dry rot

• Loosening of nails, which may be evidence of adverse movement of the spar
• Moist or wet wood
• Erosion of varnish or finish that could lead to the growth of fungus within wood fibers
• Any observable stains, which are accompanied by rot

What Is Corrosion?

Corrosion presents altogether differently in metal aircraft. But what exactly is it? 

According to the FAA Advisory Circular AC No: 43-4B, corrosion is the “electrochemical deterioration of a metal because of its chemical reaction with a surrounding environment.” That’s a fancy way of saying rust.

• READ MORE: How to Care for Your Lycoming Camshaft

Corrosion is a natural process that affects metal through chemical or electrochemical reactions, transforming it into compounds like oxides, hydroxides, or sulfates. Unlike erosion, which damages materials through mechanical action, corrosion occurs as metals seek to revert to their natural state, the FAA said.

For corrosion to take place, four specific conditions must be met:

1. Presence of an anode or a metal that will corrode
2. Presence of a cathode, a dissimilar conductive material that has less tendency to corrode
3. Presence of an electrolyte, a conductive liquid
4. Metal-to-metal contact or a fastener that usually makes electrical contact between the anode and cathode

Elimination of any one of these conditions will stop corrosion. 

More Than an Airframe Problem

Corrosion is the silent killer of aircraft, and if left undetected, it could wreak havoc on your equipment and operation.

When most of us think about corrosion, it is typically in a highly exposed environment that is unprotected from the elements, like wheel wells. However, corrosion can occur anywhere on the aircraft, including, but not limited to, propellers, avionics, and engine parts.

The FAA outlines methods, techniques, and practices acceptable for inspecting, preventing, controlling, and repairing corrosion on avionics systems and equipment in its advisory circular AC 43-206.

“Studies have shown that 20 percent of avionics equipment failures are a direct result of corrosion,” the FAA said. “Even minute amounts of corrosion can cause intermittent malfunctions or complete equipment failures.”

Another critical area of concern for corrosion is propellers. According to legacy prop maker Hartzell Propeller, the different versions of propeller corrosion include uniform surface corrosion, pitting corrosion, intergranular corrosion, and stress corrosion/cracking.

“Keep in mind that the forms of corrosion vary with the type of metal involved, the age of the aircraft, atmospheric conditions, and the length of time that the aircraft is exposed to corrosion,” the company said.

The post Identifying Corrosion in All Its Forms appeared first on FLYING Magazine.

Diving deeper into the world of aviation spark plugs, we will pull back the cowling and affix our inspection mirror to discuss the types commonly used in different aircraft models, insights into their maintenance, and recommendations for their replacement. 

Understanding the Basics

At their core, spark plugs are devices that deliver electric current from an ignition system to the combustion chamber of an engine, igniting the compressed fuel/air mixture by an electric spark. Properly functioning spark plugs are essential for smooth engine operation and optimal performance.

Types of Aviation Spark Plugs

“The two major types of electrodes in today’s spark plugs include the dual nickel alloy massive electrode and the single Iridium fine-wire electrode,” saidAlan Woods, sales manager for piston and power at Champion Aerospace in Liberty, South Carolina. “The nickel alloy electrode design allows for a long-lasting spark plug [300 to 500 hours] at an affordable price. The Iridium fine-wire electrode design offers TBO life [2,000 hours plus] but at a higher cost due to the high cost of Iridium [$4,000 per ounce].”

Massive Electrode Spark Plugs

Massive electrode spark plugs are the most commonly used type in general aviation. They feature large electrodes designed for durability and extended use.

• READ MORE: Intro to Aviation Spark Plugs

Massive electrode plugs are critical features in terms of durability. They can withstand significant wear and tear, making them ideal for aircraft that undergo frequent and long flights. Massive electrode plugs are also cost-effective. They are generally more affordable than their counterparts, the fine-wire spark plugs. Another attribute is their ease of maintenance. Due to their stout construction, massive electrode plugs are easier to clean and maintain.

There are a few downsides to massive electrode plugs. Over time, massive electrode spark plugs can suffer from performance issues due to electrode wear and increased gap size, leading to less efficient combustion. They are also heavier as the larger electrodes add to the weight, which can be a minor concern in aircraft performance calculations.

Fine-Wire Spark Plugs

Fine-wire spark plugs are designed with thinner electrodes, often made of precious metals such as platinum or Iridium, to provide superior performance and longevity.

The fine-wire plug offers improved ignition over massive electrodes, giving the fine-wire electrodes a more concentrated spark and leading to better combustion and engine performance. They also last longer because they are constructed using durable materials, such as platinum and Iridium, reducing the frequency of replacements. Fine-wire plugs are also lighter than massive electrode plugs, contributing to overall aircraft efficiency.

• READ MORE: Breaking Down Sudden Stoppage Inspections

These enhanced attributes come with a cost. Aircraft fine-wire spark plugs are substantially more expensive than massive electrode spark plugs. They also require careful handling during maintenance to avoid damaging the fine electrodes.

Choosing the Right Spark Plug 

The choice between massive electrode and fine-wire spark plugs often depends on the specific requirements of your aircraft and your flying activity. Massive electrode spark plugs might be more suitable if you fly frequently and cover long distances due to their durability and cost-effectiveness. Fine-wire spark plugs could be the better choice if you prioritize engine performance and are willing to invest in premium parts due to their enhanced ignition efficiency and longevity.

Fine-wire plugs provide a more efficient burn rate and last longer at a much higher purchase price, according to Vince Bechtel, director of aftermarket sales at Tempest Aero Group, which entered the aviation spark plug market in 2010 by acquiring the Autolite brand. A relatively small niche market, the company represents about 10 to 15 percent of the aviation aftermarket. Turbocharged aircraft flying at higher altitudes favor fine-wire plugs, according to Bechtel.

• READ MORE: Servicing Cessna 172 Stuck Exhaust Valves

Maintenance and Replacement Recommendations

Proper maintenance and timely replacement of spark plugs are crucial to avoid engine misfires and ensure smooth operation. Some tips:

●      Regular inspections: Conduct routine inspections every 100 hours of flight time or as your aircraft’s manufacturer recommends. Check for signs of wear, fouling, or damage. Common issues include carbon buildup, oil fouling, and electrode erosion.

●      Cleaning: Use an approved spark plug cleaner to remove carbon deposits and debris. Be cautious with fine-wire spark plugs to avoid damaging the delicate electrodes.

●      Gap checking: Ensure the spark plug gap meets the manufacturer’s specifications. A correct gap is crucial for optimal spark plug performance. Adjust the gap if necessary using appropriate tools.

●      Replacement: Replace spark plugs at the manufacturer’s recommended intervals or if significant wear or damage is observed during inspections. Always use spark plugs that meet the specifications of your aircraft’s engine model.

“Honestly, the biggest issue I see is over-cleaning,” Bechtel said. “Individuals and shops tend to clean plugs until they look brand new out of the packaging. The only thing this does is wear out your electrodes and insulator faster, preventing you from getting the full life out of a set of plugs.”

Troubleshooting Common Spark Plug Issues

Even with regular maintenance, spark plug issues can occur. Some common problems and their potential causes include:

Engine Misfire

• Caused by worn electrodes, incorrect gap, or fouled plugs.
• Solution: Inspect, clean, or replace the spark plugs as needed.

Hard Starting

• Often due to spark plug fouling or improper gap.
• Solution: Check and clean the spark plugs and correct the gap.

Poor Engine Performance

• Can result from degraded spark plugs or incorrect heat range.
• Solution: Verify that you are using the correct type and heat range of spark plugs for your engine.

The introduction of fired-in suppressor seal technology, or FISS, is a recent advancement in aircraft engine spark plugs.

“This technology eliminates the high-voltage silicon resistor, which is prone to resistance value increases over time,” Woods said. “The FISS technology incorporates fired-in conducting and suppressor glasses that establish the resistance value of the spark plug. This means that the end user has a stable resistance value over the entire life of the spark plug. With the introduction of electronic ignition, spark plug designs will evolve with wider gaps to handle the increased energy being produced.”

Understanding the various types of aviation spark plugs and their benefits and limitations can help you make informed decisions about aircraft maintenance. Whether you choose massive electrode spark plugs for their durability and cost-effectiveness or fine-wire spark plugs for their superior performance and longevity, regular maintenance and timely replacements are critical to engine operation. 

Please consult your aircraft’s technical publications and an A&P mechanic to ensure your spark plugs are in an airworthy condition.

The post Keeping Current With Aviation Spark Plugs appeared first on FLYING Magazine.

As many of you know, I owned and operated an aircraft engine shop for more than a decade and consistently handled sudden stoppage inspection cases. The jobs were so common that we even had T-shirts printed with the phrase, “Things get hot when the big fan stops.” Sometimes, humor can help take some of the sting away. Like the late Jimmy Buffet sang, “…if we couldn’t laugh, we would all go insane.” Aircraft ownership and maintenance will do that to you. This is why we all gather here to swap stories, support each other, and maybe learn a little something along the way.

Disclaimer: Today, we are discussing air-cooled reciprocating engines. The criteria are different based on engine type.

Defining a Propeller Strike

As with many things in aviation, the definition of propeller strike is hotly debated. The same is true of what maintenance evolution is applicable after determining if a prop strike occurred. More on that later. First, let’s determine what a propeller strike is.

The FAA sets the bar high by including a sudden stoppage question in the FAA-S-8081-28A Aviation Mechanic Powerplant Practical Test Standards. Part C on engine inspection, drawing on the references from 14 CFR Part 43; AC 43.13-1B and FAA-H-8083-32, states the objective is to determine that the applicant can demonstrate “knowledge of an inspection required after a potentially damaging event, including but not limited to any of the following: sudden stoppage, over speed, or over temperature.” Even among A&Ps, there is a wide disparity in interpreting the definition, with subsequent actions also in question.

Some A&Ps are jacks-of-all-trades, while others are highly specialized. Based on experience, I recommend dealing with specialists regarding critical components such as avionics, powerplants, and propellers.

• READ MORE: 5 Attributes of a Top-Notch Maintenance Provider

What constitutes a propeller strike? Let’s check with the experts and see what the OEMs say.

According to Service Bulletin SB96-11B, Continental Aerospace Technologies defines a propeller strike as: “(1) any incident, whether or not the engine is operating, that requires repair to the propeller other than minor dressing of the blades as set forth in Part I, B of this Service Bulletin or (2) any incident while the engine is operating in which the propeller makes contact with any object that results in a loss of engine rpm.”

Our friends in Lycoming County, Pennsylvania, in their Service Bulletin No. 533C, define a prop strike as:

• Any incident, whether or not the engine is operating, where repair of the propeller is necessary.

• Any incident during engine operation where the propeller has an impact on a solid object. This incident includes propeller strikes against the ground. Although the propeller can continue to turn, damage to the engine can occur, possibly with progression to engine failure.

• Sudden rpm drop on impact to water, tall grass, or similar yielding medium where propeller damage does not usually occur.

How It Happens

During my engine shop days, I can say with certainty that no two sudden stoppage inspections were alike. Scratch that. We did have one client who cranked his Cessna’s engine with the nosewheel tow bar still attached to the aircraft not once, but twice. True story: The first incident occurred, and the owner dutifully called the shop for an estimate. We bid the job, won the business, and carried out the maintenance action to get the good doctor (he was an oncologist) airborne once again. Or so we thought.

Twas less than a fortnight before he rang the shop again. After installing the engine, the mechanic reconnected the baffling, linkage, and appropriate hoses, instructing the owner to crank it up—yes, with the towbar once again still attached. At least the parts bill of materials (BOM) was easy to create. In fairness, his ground support person should have alerted him that the tow bar was in place. As with most aircraft incidents, it was a breakdown of systems, communication, and practices mixed with bad luck.

• READ MORE: Servicing Cessna 172 Stuck Exhaust Valves

We also saw plenty of the traditional ways propeller strikes occur. Taildraggers are in danger of ground looping. Tricycle gear aircraft brake too hard and dip the nose or hit a depression on a grass field and catch the propeller. Once, a client called to say they approached their aircraft to do a walk-around and found shattered glass from a blue taxi light lens in the cowling during the preflight inspection. There was nothing in the logbook about this. I had one customer taxi into a hangar door and another into a second aircraft.

One of the pricier inspections we accomplished was a Piper Navajo that landed gear up. Upon tearing down the engine, we found special H5 Lycoming connecting rods. There was no way to know this during the estimate phase, and we had to tell the client that his bill had just gone up. All of this is to say propeller strikes are more common than one might think.

There is one other hazard that causes prop strike concerns for pilots—wildlife. Most everyone knows the story of Captain Sully and the “Miracle on the Hudson.” Did you also know that according to the FAA Wildlife Strike Database, about 272,000 wildlife strikes with civil aircraft were reported in the U.S. between 1990 and 2022? That is a lot of damaged aircraft.

The encounters are only sometimes birds. Some pilots report striking white-tailed deer and even elk in the northern states. The FAA launched the Wildlife Hazard Mitigation program to help counteract the effects of wildlife on airports. On the program website, the FAA states that “during the past century, wildlife-aircraft strikes have resulted in the loss of hundreds of lives worldwide, as well as billions of dollars in aircraft damage.”

Incident Confirmed—Now What?

As certified aircraft mechanics, the FAA mandates we operate with the highest degree of safety conscience, and demand the same of those we work with. An excerpt from the Mechanic’s Creed states, in part, that “I shall never knowingly subject others to risks which I would not be willing to assume for myself, or for those dear to me.” In layman’s terms, we often ask ourselves, would you fly behind it? Once you qualify the occurrence as a propeller strike, what happens next? There are three distinct camps in this regard. So as not to sound inflammatory and stir emotions, let’s designate them as teams A, B, and C.

Strictly for identification purposes, let’s say Team A equals “all good, keep flying,” Team B “better do the minimum,” and Team C “conscientious.” This division stems from misconceptions about what to do after a propeller strike. The major engine manufacturers, Lycoming and Continental, are clear on the action needed in their respective service bulletins. For Lycoming applications, some have attempted to circumvent this by their interpretation of AD 2004-10-14. Team B will point to the statement: “Remove the existing gear retaining bolt and lockplate from service, and install a new bolt and lockplate, in accordance with steps 6 and 7 of Lycoming MSB No. 475C.” It believes this is the bare minimum needed. It argues that an Airworthiness Directive (AD) takes precedence over a service bulletin. However, this AD references SB475, not SB533C. Are you confused yet?

• READ MORE: Testing the Hardware After a USM Retrofit

Like every other aircraft maintenance evolution, the bottom line is comfort. Are you comfortable accomplishing the bare minimum and avoiding the messiness and expense of an engine teardown? Just know that we have found cracked crankshafts before when doing the magnetic particle inspection. When asked about potential damage on its website in an article entitled “Prop Strike: What’s Next?” Hartzell Propeller said, “Even if there’s no visible damage to the propeller, there may be hidden internal damage to the propeller, governor, crankshaft, and other components that can cause engine failure later in the engine’s life, if not immediately.” That sounds definitive to me.

A chance to perform maintenance, like that following a prop strike, is also an opportunity to find other issues. Some argue that mechanics cannot unsee issues, which will increase the repair cost. Dare I say there is no such thing as too much maintenance? I recall an instance when a Beechcraft Baron B58 operator suffered a propeller strike and contracted us to perform the inspection. The engine was a Continental IO-550-C model configured with a front-drive alternator. During disassembly, our technician noted the lock tabs of the face gear hardware were not bent, locking the bolt in place. Subsequently, this caused a crack in the crankshaft ring gear mounting flange. It scrapped the crankshaft. This customer operated a fleet of Barons, and we sent word to them to inspect the remaining aircraft.

This issue is just one example of many we found through engine maintenance. Another common squawk involves camshafts going bad. Typically caused by corrosion, the camshaft will begin to wear abnormally and spall the lifter. While the charges for the parts to repair these discrepancies fall outside the scope of maintenance for the sudden stoppage inspection, the labor is covered and, therefore, essentially free. A real bargain. Another key point I highlight to my clients: Do you want to find out about that issue in the shop or at altitude?

Tap into Knowledge

The aircraft reciprocating engine business is a tight-knit group of folks quick to help each other out. That’s what I love about this industry. This is especially important since, while most information is easily accessible, there are some things that are either not readily available or just industry tips one picks up through the years.

For example, did you know that your dry air vacuum pumps require replacement after a propeller strike? Consult Tempest Service Letter SL-008, with an opening statement that reads: “When a Tempest engine-driven air pump is subjected to sudden engine stoppage (for example, propeller strike during a gear up landing), the rotor and vanes of the pump may sustain damage. This damage may not be evident by rotating the pump or by visual examination.” What about Rapco? Same story. Refer to Service Letter RASL-003, which states: “When a Rapco Inc. pneumatic pump has been subjected or is suspected of having been subjected to sudden engine stoppage or propeller strike event, it is mandatory to replace the affected pneumatic pump before further flight, in accordance with the procedure outlined below.”

What about magnetos? Champion Slick Service Letter L-1363 states that “magnetos must be overhauled after a lightning strike on the aircraft, a sudden engine stoppage, prop strike, or immersion.” Are you picking up on the pattern yet?

Here is a fun fact: Lycoming has a surprise for the newer model engines. Earlier, we mentioned Lycoming Service Bulletin No. 533C. Reading through the SB, you will see “NOTICE: Roller tappets, counterweight rollers, and bushings must be replaced.” You read that correctly: Replacing roller tappets during a sudden stoppage inspection is mandatory.

How is someone supposed to keep all of this straight? You’re not. Aviation is a team sport. Do your homework and trust the professionals. Most engine shops are willing to go the extra mile to help you. Ensure you work with one with high standards. The rules are constantly changing. In years gone by, Lycoming allowed certain repairs for a bent propeller flange on engine crankshafts. With the publication of Service Bulletin No. 201F, this is no longer the case. The SB reads, in part: “Lycoming Engines no longer allows bent crankshaft flanges to be ground or repaired to restore maximum run-out. As per Service Bulletin 533B, if the crankshaft is bent, it must be replaced.” A good shop will help you decipher this.

Hidden Problems

I wanted a firsthand account of the “to tear down or not tear down, that is the question” debate, so I checked in with JD Kuti from Pinnacle Aircraft Engines in Silverhill, Alabama. When asked if his team ever found issues during teardown after a propeller strike, Kuti responded with a resounding: Absolutely!

Here are the common issues discovered:

• Crankshaft flange bent

• Crankshaft cracked at flange or slinger ring

• Crankcase cracked

• Gear teeth cracks

This feature first appeared in the April 2024/Issue 947 of FLYING’s print edition.

The post Breaking Down Sudden Stoppage Inspections appeared first on FLYING Magazine.