Aiming for Blue Skies

When is an Aircraft too Old? What Determines an Airplane’s Lifespan?

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You may be aware that there are many old airplanes still flying in today’s skies. Are you aware of how the lifespan of an airplane is determined? The subject is an interesting one, and the answer is not as simple as you may have thought.

Pressurization Cycles Determine Aircraft Age

aircraft-life-spanFor an airplane, it’s not the absolute number of years that contributes to its age. Instead, the airline industry uses a concept known as “pressurization cycles” to keep tabs on the effective lifespan of aircraft. The term refers to the amount of time that the aircraft is kept under pressure from flight. The pressure of flight stresses the fuselage and wings. Over time this stress effects the airplane’s structure which makes flight increasingly more dangerous.

  • The lifespan of aircraft is determined by the manufacturer.
  • The age is calculated based on pressurization cycles. As a rule of thumb, each cycle involves “takeoff/landing.”
  • Fuselage and wings suffer stress from pressurization, including on “short hauls.”
  • Airlines follow manufacturer’s directions for “trouble free” maintenance.
  • Nondestructive evaluations (NDE) are used during the life of the airline to inspect for damage.

Airlines have to make a decision on how long their aircraft is used based on balancing the needs for profitability and public safety. There are no hard and fast “rules” concerning the exact age or number of cycles when a company would retire an airplane. If repairs came due that were prohibitive in cost, that would hasten the decision to retire the aircraft.

Economic Factors Decide on Airplane Life

Airplanes often are upgraded based on economic reasons and the changing tastes of consumers. There are planes that are capable of flying for decades, but it’s doubtful that commercial airline passengers would be willing to pay top dollar to fly them, especially with more modern options being available. Airplane manufacturing makes new models that offer more features and higher chances of profitability in the hopes of convincing airlines to upgrade their fleets. Airlines with the newest planes tend to have more customers flying at any given time because of the increased comfort.

Even though it’s not completely accurate, the most basic explanation of determining aircraft’s lifespan is this: the number of takeoffs and landings ultimately decide how long an airplane lasts. The more an aircraft is used, the more pressure the structure endures and the closer the craft gets to reaching its maximum service. The good news is that a plane that has had a lot of takeoffs and landings, it’s assumed, will have earned a hefty profit over the course of its lifetime.

Preparing to Store Your Aircraft for Winter

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You may be prepared for winter, but is your light aircraft also ready? Chances are that when temperatures plummet and the snow moves in you’re not going to be flying in a hurry. The aircraft at greatest risk are those that are parked outside, and those along the coast or close to lakes and rivers where corrosion damage is a major risk. Those facing minimal risk are the ones that are in the few dry parts of the country where industrial pollutants are not an issue.

While the best solution is to store aircraft indoors, in a hangar, this isn’t always possible. But whether it is or not, there are steps that owners can take, including removing engines from the body of the aircraft for the winter months.

Small Aircraft Engine Care

US engine manufacturer, Lycoming warns that active corrosion can be found on the cylinder walls of new engines that haven’t been operated for even short, two-day periods of time. On the other hand, those that have been used for at least 50 hours acquire a kind of “varnish” that protects them from corrosion, and they can be left inactive for weeks without any danger of corrosive damage.

Engines that are not going to be used for flight need to Winter | Aircraft | Storagebe stored or preserved in some way to minimize any possibility of corrosion. Acceptable methods are aimed at preventing moisture and other agents that might cause corrosion from affecting the metal surfaces in the engine.

Lycoming also warns that engines should not be pulled through by hand to minimize corrosion and rust because the rings have the effect of wiping oil from the walls of cylinders and reducing the lubrication needed for other parts of the engine including the cam and cylinders. The company notes that pulling the prop before starting the engine is a different issue because it does lubricate the parts. It also has the effect of checking valve condition.

Preservation of Engines That Will Not be Active for a Month or More

It is essential to “preserve” engines that will not be active for more than a month, particularly when the aircraft is located in a humid environment or somewhere close to salt water.

Of course the process that should be followed will depend on the engine make and design, and the manufacturer’s instructions should always be followed. These will normally include a basic procedure including:

  • Draining lubricating oil from the sump and replacing it with a preservative oil
  • Operating the engine to “normal” temperatures before shutting down
  • Removing spark plugs, spraying the holes with a preservative oil mixture, and then replacing the spark plugs
  • Installing dehydrating agents (desiccants) and moisture-impervious material to protect intake and exhaust passages
  • Tagging the propeller so that anyone with access to the aircraft knows that the engine is “preserved” and that they must not turn the propeller

While corrosion-preventive compounds do effectively work as insulators from moisture over fairly long periods of time, they can dry out when solvents evaporate. For this reason, if engines have been removed from aircraft, they should be stored in containers that are airtight, and the containers should be packed with dehydrating agents and sealed. Adding cobalt chloride to silica gel (which is the most common desiccant) can be very effective because the bright blue color from the cobalt chloride will show low moisture levels. If the blue gets lighter (changing from lavender to pink and even white), this indicates higher humidity levels. The ideal is that when the color remains blue the conditions for storage are safe and dry.

Other Safeguards for Your Aircraft

If you are planning to store your aircraft engine, it really should be coated with a compound that will prevent it from corrosion. Close or plug holes and treat propeller shafts or wrap them with a suitable barrier paper. Purge fuel systems.

This said, there are different recommendations for different aircraft, and it is essential that you familiarize yourself with specifics. For example if your plane has rubber-type flexible fuel bladders, it is best to keep the tanks full to ensure that the membrane doesn’t crack.

Returning Aircraft to Service

Once winter is over, all seals, tape and desiccant bags must be removed and any residue from tape must be cleaned. Any dehydrator or spark plugs that have been used should be removed. Preflight checks are also critically important for safety reasons.

Long-term engine preservation can result in large quantities of oil being trapped in the cylinders. The oil should be drained before the engine is rotated otherwise you risk piston, crankshaft or other damage.

If you are in any doubt, contact the manufacturer of the aircraft and/or the engine.

The Importance of Aircraft Maintenance and Service

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All aircraft, big and small, must be serviced regularly, according to the specifications provided by the manufacturer. But there are different types of service and maintenance checks, and also different ways that service is scheduled.

Additionally, all planes should be regularly inspected before each flight.

While individual manufacturer requirements do differ, light planes generally need an annual inspection to check the condition of the plane, as well as service maintenance after a specified number of flying hours.

Service and Maintenance Checks

It should be obvious, but the more you fly your plane, the more frequently you will need to have it serviced. This is why manufacturers commonly specify flight hours rather than timeframes for service and maintenance checks. So, for instance, an annual condition check carried out to ensure that the plane conforms to the airworthiness “type” certificate issued when it was originally inspected after manufacture might be required more frequently (perhaps every 100 hours) if the plane is used often, or for commercial purposes. For this check, all access plates are normally removed, and everything that can possibly be checked, is checked, including retractable landing gear and related mechanisms, as well as engine compression.

More frequent maintenance service checks would include checking of critical bolts including those that connect the propeller to the engine, as well as replacement of engine oil. Oil changes could be required as frequently as every 25 hours flying time.

Aircraft tires, like those used for automobiles, must be replaced when the rubber tread begins to wear. Generally this will be determined by the friction caused between the tires and airfield surface, which in turn will be directly affected by the number of landings made in the plane.

Visual Aircraft Inspections

airplane-service-inspectionAll light aircraft should be inspected visually before each flight. Typically the pilot or co-pilot will check fuel levels, engine oil level, cable connections and internal parts, and generally look out for any damage that might have occurred. It is always good to check the area below where the plane has been parked to make sure there isn’t evidence of leaking fluids.

Federal Aviation Administration (FAA) Requirements for Airworthiness

While FAA maintenance checks are more stringent for airlines carrying passengers, as well as commercial planes, and military aircraft, the types of checks followed provide additional insight into how often aircraft should be serviced. These do not preclude the checks and inspections required by the manufacturer.

FAA checks are commonly referred to as A, B, C and D checks, D being the most comprehensive.

A checks are done after 125 flight hours, depending on the type of aircraft and aircraft cycle of takeoff and landing, and take between 20 and 50 man hours to complete. A checks on airliners are usually performed at the airport gate, overnight.

B checks are performed, on average, every six months. They take between 120 and 150 man hours to complete, and are usually executed in the aircraft hangar.

C checks are commonly performed every two years, or according to the flight hours defined by the manufacturer of the aircraft. This is an extensive check and involves the inspection of most of the aircraft components. It can take one to two weeks to complete, and as many as 6,000 man hours. These checks are generally performed in hangars located at a dedicated maintenance base.

D checks are comprehensive and sometimes referred to as a “heavy maintenance visit.” They are done every six years or so and involve thorough inspection and a complete overhaul. They can take as many as 50,000 man-hours over a period of two months to complete. Because these checks are so expensive, many airlines prefer to phase their craft out instead.

Where to Go to Service Your Aircraft or Buy Parts

While many service centers specialize in maintaining specific types of aircraft, there are also companies that specialize in the repair, supply and overhaul of a wider range of fixed-wing planes. Some, like Prime Industries, also supply quality parts and components for a wide range of rotary and fixed-wing aircraft.

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