As you gaze into the sky and look about the horizon, an ascending airplane catches your eye— you marvel in its magnificence and can’t help but to feel inspired by the wonders of flight. The aircraft travels so effortlessly from afar, almost as if it can fly forever. As flawless as it might seem, there comes a time when every plane must be decommissioned. So, what determines the lifespan of a plane? Where do they go after they can’t fly anymore?
The determined aircraft lifespan is established by the manufacturer. It is not measured in total years of service; instead, it is calculated by the amount of pressurization cycles it endures. This refers to the amount of time that the aircraft is kept under pressure from flight, and the amount of stress put on the fuselage and wings. Short-haul flights often grant shorter lifespans while long-haul flights allow for longer lifespans. Shorter flights lead to more pressurization cycles, shortening longevity. A Boeing 747 can withstand approximately 35,000 pressurization cycles—roughly 165,000 flight hours. Airlines must decide on when to retire an aircraft based on profitability and public safety.
Airlines are continuously upgrading their aircraft due to changing tastes of consumers. There are planes that are capable of flying for several decades, however, commercial airline passengers wouldn’t be willing to pay top dollar for them without integrated advancements. Manufacturers commonly offer upgraded features which leads to a decrease in demand of older model aircraft, which also contributes to its lifespan. Airlines with the newest planes tend to have more customers flying at a given time because of increased customer satisfaction.
Decommissioned aircraft eventually make their way to the southwestern American desert that includes parts of California, Arizona, New Mexico, and Texas. Massive aircraft storage sites house these planes in arid climates which slow down the rusting process, allowing the spare parts to be used or sold later. Secondhand aircraft parts are hot commodities as most of them still function and are significantly cheaper than new ones. Almost every part of an airplane can be recycled for use in newer planes.
Engines are in high demand because their turbines contain rotating blades that must be swapped out regularly to stay in compliance with safety regulations. Trading out these blades for used ones can cost upwards of two million dollars, roughly half the price of buying new parts. Once an aircraft has been stripped of all of its usable parts, the metal frame is melted down and used as scrap. In some cases, the raw materials are repurposed. Multiple recycling operations in the US and Europe specialize in this processing. The next time you drink from an aluminum can, consider that what you’re holding may have flown across the skies at one point!
There are five basic types of Army/Navy (AN) connectors used on aircraft: Class A, Class B, Class C, Class D, and Class K. Class A-D connectors are made of aluminum while Class K is made of steel. Class A is a solid, one-piece back shell connector and is general-purpose. Class B back shell separates into two parts along the length and is used where it’s important that the soldered connectors are readily accessible. Class C is a pressurized connector and has inserts that are not removable. They are used on walls or bulkheads of equipment that is pressurized. Class D are moisture and vibration resistant and have a sealing grommet in the back shell. Class K is a fireproof connector and is usually longer than other connectors.
When frequent disconnection is required, connectors facilitate maintenance. Connectors are susceptible to corrosion because of condensation within the shell. Because of this, waterproof features have been developed. If a connector is not waterproof, it may be treated with a waterproof jelly.
There are about four steps to assembling a connector to a receptacle. The first step is to locate the proper position of the plug to the receptacle. The second is to create a slight forward pressure to start the plug into the receptacle. The third step is to push the plug in and tighten the coupling ring. And the fourth step is to use connector pliers and tighten the coupling rings. It’s important to not use force to mate connectors and receptacles; don’t use a hammer to force a plug into the receptacle and don’t use a torque wrench or pliers to lock coupling rings. Doing so can cause irreparable damage to the connectors.
And there are about three steps to disassembling a connector. The first step is to use connector pliers to loosen the coupling rings. The second step is to pull on the plug body and unscrew the coupling ring. And the third step is to protect the plugs and receptacles with caps or plastic bags; this will prevent debris from entering the items.
A conduit is a tube that protects electric wiring and is used in aircraft to protect wires and cables. It comes in metallic, nonmetallic, rigid, and flexible forms. Many installers will account for ease of use for maintenance and leave some room for possible circuit expansion in the future. Fittings are used at the end of a conduit to make it less vulnerable and if a fitting is not used, the conduit end should be flared. This will prevent wire insulation damage. It’s important to pay close attention when installing a conduit because it shouldn’t be located where it may be used as a handhold or footstep. Installers need to provide drain holes at the lowest point in a conduit run. And, the conduit needs support to prevent chafing and avoid stressing its end fittings. When a conduit is damaged, it should be replaced as soon as possible so the wires do not get damaged.
There are three kinds of engines that power most aircraft: piston engines, jet engines, and rocket engines. Each of these have the same basic principles; the engine mixes fuel with an oxidizer in a combustion chamber, the mixture is ignited, the burning mixture creates hot, expanding gases, and these gases will either produce thrust directly or are used to push a piston or drive a turbine. There are different variations of a jet engine, also known as a gas turbine. Most have the same five key parts: an inlet, a compressor, a combustion chamber, and a turbine with a driveshaft running through them.
Turbojets are the basic jet engine. They produce a steady amount of power and are useful for low-speed jet planes that do not have high payloads. Air passes through an inlet, is compressed to 3 to 12 times its existing pressure, fuel is added and ignited in a combustion chamber, and the hot air then passes through a turbine and is expelled past a nozzle. The turbine extracts energy and powers the compressor. An afterburner may be used to increase the temperature of the gas ahead of the nozzle, which results in the capacity for higher speeds.
Turboprop engines have the same components but transfer energy from the gas to the turbine which will then turn a shaft that drives a propeller. Thrust is produced from the rotating propeller instead of expelled gas. It has better propulsion efficiencies at speeds below 500 mph. Turboshafts are similar to turboprops, but instead of driving a propeller, it provides power to a helicopter rotor.
Most modern airliners use turbofans because they are quieter and have better fuel efficiency. They operate the same way as the previous two engines however, they have a large fan at the front of the engine. A portion of the air will pass through the gas generator and the remainder passes through the fan and is ejected directly into the jet stream or mixed with the gas-generator exhaust. This is called a bypass system and increases thrust without increasing fuel consumption.
Ramjets are in the shape of a rapidly tapering nozzle. This shape naturally compresses the incoming air, so ramjets do not have compressors or turbines. They require an assisted takeoff and are used for guided-missile systems and space vehicles. The difference between a ramjet and a scramjet is that a ramjet compresses the air and reduces it to subsonic speeds while a ramjet allows the airflow to remain supersonic and the plane can go much faster.
Although tow bars are essential equipment for aircraft emergencies, tow bar maintenance is often overlooked. Just like with any other piece of equipment, tow bars should have a brief daily inspection and routinely scheduled thorough maintenance in order to ensure full functionality. Because there are many types of tow bars, it’s best to at least become familiar with some of the more common tow bar parts to ensure inspection goes smoothly.
Shear pins should be one of the first parts to be inspected because they carry the majority of the load when the aircraft is being pushed or towed. They are designed to have a breaking point, reducing the possibility of damage to the aircraft in the event of too much strain. The pins should be removed and checked for any sign of stress, indents, cracks, or other irregularities. The pin should be immediately replaced if any signs of strain are observed.
The head mechanism includes many moving parts which should be inspected on a regular basis. Each moving part should be carefully inspected and checked for lubrication. Improper lubrication can lead to premature wear and tear.
The tow bar body should be inspected regularly for any cracks. If any damage is observed, it should be taken to a certified welder for repairs following proper protocols and procedures. If there is any other severe damage to the body, the unit should be taken out to be serviced or replaced right away. Continued use will only result in further complications.
The wheels are typically not something that you might consider as needing inspections. The wheels have specific parts which could inhibit movement, so it’s important to make sure the lug nuts are tightened and checked for any cracks on the wheel. If any irregularities are noticed, it should be brought to attention and remedied.
Jet engines are complex pieces of machinery that propel giant metal contraptions tens of thousands of feet in the air. They’re a type of combustion reaction engine that discharge fast-moving streams of fluid and generate thrust by propulsion. They’re made of different parts: a fan, compressor, combustor, turbine, nozzle, and exhaust.
The fan, or the air inlet, is a large spinning fan made of titanium that sucks in a large quantity of air. After sucking, it speeds up the air and splits it into two parts: one that goes through the core part or through the center of the jet engine where it is acted upon by other engine components, and one that “bypasses” the core and goes through a duct that surrounds the core and produces much of the force that propels the airplane forward.
The compressor is the first component of the core. It’s made up of fans with many blades attached to the shaft and has many different stages, each consisting of rotating vanes and stationary stators. As air goes through the compressor, the heat and pressure increases, the energy is derived from the turbine and passed along the shaft, and then the compressed air is forced into the combustion chamber.
In the combustor, there are as many as 20 nozzles to spray fuel into the airstream, and the mixture of air and fuel catches fire. The fuel and oxygen burning produces hot expanding gases, leading to high temperatures and high-energy airflow.
The high-energy airflow leaves the combustor to spin the turbine, a series of bladed discs that act like a windmill. The turbines are linked by a shaft to turn the blades in the compressor and to spin the intake fan at the front. This process takes some energy from the high-energy flow. In some turbine engines, additional energy is used to drive things like the propellers, bypass fans, and rotors.
The last part is the nozzle and exhaust, where the thrust is actually produced. The hot energy-depleted airflow that passed through the turbines and the colder air that bypassed the core converge and exit the nozzle, exerting a force that propels the aircraft forward.
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