Auxiliary power units are engines, motors, and power units that provide vehicles with energy for functions other than propulsion. They are used in larger vehicles, such as aircraft, marine vessels, and some larger land vehicles to perform tasks such as starting main engines, heating motor blocks, and charging batteries. They can provide power in electric, pneumatic, and hydraulic forms.

In aircraft, APUs assist in starting the primary engine or engines, generate power for the aircraft during pre-flight checks, and energize cabin amenities such as lights and heating while the engines are off. APUs come in various different types, serving different purposes, and draw power from multiple kinds of sources, including batteries, hydraulic accumulators, and combustion engines.

APUs consist of three basic sections. The first is the power section, which is typically a gas generator for producing the device’s shaft power. Next is the load compressor, a shaft-mounted compressor that provides pneumatic power (some APUs extract bleed air from the power section compressor). Lastly is the gearbox section, which transfers power from the main shaft of the engine to a generator for electrical power. Power is transferred from the gearbox to the fuel control units, lubrication modules, and cooling fans.

Auxiliary power units in commercial airliners take the form of a small turbine engine, usually mounted in the tail. The APU functions just like the turbine engines that provide thrust for the jet, but unlike them, the APU does not provide thrust to the aircraft. The engine drives a generator, which in turn powers the electrical systems onboard like lights and heating while the aircraft is on the ground. In flight, power for these systems is provided by the main engines, and the APU is shut off to save on fuel.


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While functionally and chemically similar to the gas used in automobiles, aviation fuel is  different in several important ways. Like gasoline, aviation fuel used by aircraft is made up of numerous different hydrocarbons. The longer the hydrocarbons are and the higher the molecular weight of these compounds, the more chemical parameters such as melting point or smoke point differ. Gasoline, for instance, typically has seven to eleven carbon atoms with hydrogen atoms attached, while aviation fuel ranges from twelve to fifteen carbon atoms with attached hydrogen atoms. These chemical parameters can have an enormous influence on the quality of the fuel, with one of the most important for quality control being the viscosity.

Fuel purity is of course vitally important for the aviation industry. If the fuel is contaminated by water, ice can form in the fuel tanks and fuel lines while flying at high altitudes, which can disrupt the flow of fuel to the turbines and cause them to shut down. To prevent this from happening, the American Society for Testing and Materials (ASTM) develops and publishes standards for fuel purity based on viscosity. These standards are recognized and used around the world and cataloged in ASTM D1655 and ASTM D7566.

When fuel’s viscosity is too high, the injection nozzles in the turbines will struggle to spray it. This effectively shortens the working lifespan of the nozzles, which leads to higher maintenance costs and makes re-ignition more difficult if the engine fails mid-flight. The viscosity also affects the pressure drop in the fuel lines, with the greater the viscosity the higher the pressure drops. The fuel pump then has to work harder to ensure a constant flow rate so that the turbines can continue to function. On the other hand, when the viscosity is too low, the lack of lubrication in the system can lead to a total engine failure.

Fortunately, instruments called viscometers can easily check the viscosity and density of aviation fuel to ensure the fuel is within proper parameters before it is pumped into the aircraft, and numerous procedures are taken throughout storage and fueling to prevent water contamination.

At Sourcing Streamlined, owned and operated by ASAP Semiconductor, we can help you find all the fueling equipment for the aerospace, civil aviation, and defense industries. We’re always available and ready to help you find all the parts and equipment you need, 24/7-365. For a quick and competitive quote, email us at sales@sourcingstreamlined.com or call us at 1-763-401-8616.



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The FAA is responsible for noise reduction policies. The FAA program, The Continuous Lower Energy Emissions and Noise (CLEEN) encourages the creation of aircraft noise reducing equipment. The program aims to achieve environmentally friendly goals for newer aircraft models, and also encourages the retrofitting of older aircraft.  

Due to rising complaints and concerns involving loud aircraft noise, in February 2013, the International Civil Aviation Organization (ICAO) introduced a new global noise reduction standard.  Chapter 14- which applies to jet and propeller driven planes- is a more stringent standard compared to the previous standard, Chapter 4. The standard applies to newly designed aircraft operating after 2017.

The ICAO introduced a set of stages to help implement the new noise reduction standard. For an aircraft to be airworthy, an aircraft manufacturer must be compliant with the stage in which their aircraft is classified into. There are four sound stages for civil aircraft, with 1 being the loudest and 4 being the quietest. To move up a category, therefore reducing noise, an aircraft can be retrofitted with noise reduction technology. Two examples of aircraft noise cancelling systems are flap side edge liners and landing gear door liners.  Good time to introduce what those technologies are then transition into descriptions

Acoustic liners are essentially a buffeting system. As an aircraft comes into landing, the level of noise increases due to the engine running on full throttle during descent. This sparks complaints from surrounding civilian communities who live around the airport or under a flightpath.  NASA has developed two new acoustic liner systems that can be fitted to noisier aircraft that are not part of the NextGen of aircraft.

Flap side edge liners are perforated attachments that capture the noise generated by the interrupted airflow. The surface of the flap side edge liners trap the air and channel it through various vessels. The vessels are of differing lengths, therefore forcing the sound to bounce off the channels. The flap side liners can be outfitted with a stuffing such as foam, which can be tailored to absorb the sound. In a similar design to the flap side edge liners, landing gear door liners are porous in design. The liners are constructed of numerous spaces that entrap the noise generated from the air disturbance. In an added design benefit, both the flap side edge liners and the landing gear door liners adjust the boundary conditions. In doing so, the reduction liners also reduce the amount of noise being produced.

With the introduction of the ICAO standard, noise reducing technology will become more standard. In turn, the number of people who are affected by loud aircraft noise will be reduced.



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When frigid cold weather occurs, most headlines suggest that below freezing temperatures result in grounded flights. You might be surprised to hear that aircraft actually run more efficiently in relatively cold weather—here’s why.

Most commercial aircraft are designed to withstand varying temperature changes in their flight cycle. At 35,000 feet in the air, the temperature can range anywhere from -40 to -70 ?. Jet fuel freezes at about -40 ?, but redundancies on an aircraft are designed to keep all components running smoothly. As long as the aircraft systems are kept heated at minimum temperature specifications, they have no problem operating in extremely cold weather.

An aircraft engine system is also more efficient in lower temperatures. This is because the air is denser and less humid. There are more oxygen molecules readily available in a given space than during warm or hot weather. The engine is able to utilize a larger mass of air and fuel mixture, giving it more horsepower, shorter and faster take offs, and better overall performance. On hotter days, less fuel can be burned because the air is less dense and therefore not as readily available for use, therefore causing the engine to burn inefficiently and potentially cause unnecessary engine wear and tear.

Instead, the cause of flight cancellations during cold weather is often due to the presence of ice or snow on the aircraft, and at the airport itself. Ice and snow can change the pattern of airflow over the surface of an airplane, and this is especially harmful to the aerodynamics of an aircraft wing. This causes longer take off rolls and a higher stall speed in flight. Lastly, the methods needed per aircraft during icing conditions are time consuming and expensive.

For airports, cold weather can be extremely detrimental to daily operations. Flight crew and maintenance workers can only stay outside in low temperatures for a short amount of time. While the aircraft is equipped to keep itself warm, aircraft maintenance equipment is not, and can freeze easily. Ice on the tarmac results in dangerous conditions for both the airport staff and for standard takeoff and landings.

Overall, it’s not cold temperatures that cause flight cancellations. The associated dangers of icing conditions and the necessary changes in airport operations are the main contributors flight complications faced during cold weather.


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The atmospheric conditions at the typical cruising altitude of an airliner are not at all suitable for humans. Cabins are pressurized to regulate air density at those altitudes, but what protects us from the cold? At 30,000 ft., the air temperature may be approximately -47.83 ?. Imagine flying through the sky at that temperature without a cabin or a heating system. It would not work out well. There are several systems utilized by an aircraft that provide heat to the cabin.

Fuel fired heaters are mounted or portable space-heaters that obtain fuel through piping from a fuel tank, or by tapping into an aircraft’s fuel system. There are two fans in a fuel fired heater; the first fan blows air into the combustion chamber to be ignited and the second fan blows warm air into tubing directed towards the inside of an aircraft. Fuel fired heaters require electricity and are compatible with 12-volt and 24-volt electrical systems. Gas heaters need to be vented in order to prevent them from leaking dangerous gases into the cabin.

Exhaust systems may be used as a heat source for the cabin and carburetor, and are used on most light aircraft. However, defective exhaust heating systems have a few associated risks such as carbon monoxide poisoning, a decrease in engine performance, and an increased risk of a fire. Maintenance personnel need to carefully inspect the various components of this system in order to reduce the risk of the assorted dangers.

Combustion heaters are commonly used to heat cabins in larger, more expensive aircraft. Fuel is ignited in a combustion chamber or tube and the air flowing around the tube is heated and directed to the cabin. Carbon monoxide then exits the aircraft through the heater exhaust pipe. It is unlikely for carbon monoxide poisoning to occur in this type of heater. There are safety redundancies that also stop this heater from creating other dangerous situations.

Bleed air heating systems are used on turbine-engine aircraft. Compressor bleed air is transferred to a chamber and is mixed with ambient or recirculated air— the air cools off and is then routed to the cabin for heating. There are many safety features involved in this system including temperature sensors, check valves, and engine sensors.

It’s crucial to follow any original equipment manufacturer (OEM) specifications on maintaining heating systems since they can cause various dangerous situations. The safest heating systems are combustion heaters and bleed air heating systems because of their safety components.


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Though it seems inherent to include human factors in cockpit design, this notion has changed considerably since--. Today’s pilot is familiar with the presence of adjustable seats, reach envelopes, control locations, and other crucial amenities within a cockpit. This was not, however, always the case. From the U.S. Air Force to commercial jets, aircraft design was not always based on human safety and comfort.

At the dawn of its designs, cockpit layouts and infrastructure were considered incredibly unsafe. In the 1940’s, United States Air Force pilot fatalities while manning an aircraft were at a record high. At the time, and for decades to follow, the statistics used in cockpit design included only the physical measurements of a few hundred male pilots. This was also during a scientific period where personality traits were considered to be linked with physical attributes— a notion no longer deemed valid.

It wasn’t until the 1950’s, that a more reflective demographic of the pilot community was measured by the Aero Medical Laboratory at Wright Air Force Base. The results marked a new era in cockpit design and history. The findings helped advance design parameters to those used today, which are based between the 5th and 95th percentile of the average human build. These advancements have led to the inclusion of anthropometry, the science of measuring human individuals, in aviation cockpit design. It essentially includes measurements of the body when it is in movement and when it is still. The science is now a fundamental part of ergonomic design within an aircraft.

Another important human motivated innovation in cockpit design is Eye Datum, or Design Eye Reference Point (DERP). The FAA defines this as the ability to view all main cockpit instruments while maintaining a reasonable view of the outside world with minimal head movement. Identifying a design eye position is one of the first steps in the procedures used in cockpit. The modern flight deck is designed around this indispensable detail.

With these advancements in design, the modern cockpit uses a “human centered” mentality. The layout is specifically modeled on safety, comfort and organization. From display screens, to shapes and colors used, most mechanical details and parts now cater to the pilot, whomever they may be.


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As the winter season begins, it’s important to know how to preheat your plane. But first, you might ask, when should one preheat their airplane? Most experts say when the temperature hits below 32 degrees Fahrenheit, it's usually a good idea to preheat. But, if the temperature drops below 15 degrees Fahrenheit, you should definitely preheat. Preheating is essential to maintaining your aircraft, especially considering the parts for aircraft are very expensive— it is best to prevent unnecessary damage and fatigue. Airplane maintenance professionals say starting up a cold aircraft engine without preheating can cause up to 500 hours of wear on the piston.

The first option is to preheat through a forced air preheater. These are convenient and usually powered by some type of fast-heating fuel. However, there are a few downsides to this method. The forced air will not evenly heat up the ending which can result in the different temperatures throughout the airplane. This is potentially problematic because it may cause some parts to contract more than others and lead to more wear.

The second technique is to use an electric heater. This is the generally better option, but it must be installed onto the aircraft. The heating process begins once it is plugged into an outlet. It usually takes six hours to reach “thermal equilibrium” which is the when the engine is heated evenly all throughout.

The last and best method is at a heating hangar. This is an excellent method of preheating because the entire aircraft heats up to the same temperature, including the seats and oil, all at once! This method takes the longest at around 8 -12 hours, but it is the best method around. The only downside is they are not always available, but if you are able to get to one with a space availability, it is your best option.

Sourcing Streamlined, owned and operated by ASAP Semiconductor, should always be your first and only stop for all your hard to find aircraft heaters. Sourcing Streamlined is the premier supplier of forced air preheaters, electric heaters, and more! Whether new or obsolete, we can help you find all the parts you need, 24/7x365. If you’re interested in a quote, email us at sales@sourcingstreamlined.com or call us at +1-763-401-8616.


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If you’ve ever seen the back end of an airplane, you’ve probably noticed what looks like a large black dot or hole at the end of the fuselage. It’s the exhaust pipe for the small “extra” jet engine known as the APU. But what is an APU?

An APU, or Auxiliary Power Unit, is the small turbine engine used to provide additional electrical energy and normally used to start one of the main engines on larger airliners. APUs start the engines by generating auxiliary “bleed air” when there is no ground pneumatic source available. First, an electric motor starts the APU, once up and running, the APU generates bleed air which is routed to the pneumatic starters on the airplane’s main engines to spin the engine compressors for starting.

In addition to starting the engines, APUs are used to run aircraft systems on the ground when the main engines aren’t running and no ground electrical power is available. The APU can power things like onboard lighting, galley electrics, cockpit avionics, and environmental systems for pre-cooling and pre-heating. By negating the need to start the main engines while waiting for passengers to board, using the APU saves on fuel and money.

While most of an APU’s purpose is on the ground, in some instances the APU can be used an emergency electrical power source while the aircraft is airborne. But, in most cases, the APU is shut down before takeoff and reignited when the aircraft clears the runway after landing. It’s also not very accurate to say that the APU is an extra jet engine since the turbine exhaust from the APU is vented overboard, which doesn’t really help propel the aircraft forward.

Today, APUs are commonly found in medium-sized and larger civil and military jets, some turboprop aircraft, and a handful of military fighter jets. Smaller civilian jets like those used for private charters don’t have APUs because the extra weight can have much a more significant impact than it would on a larger jet.


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Imagine flying a plane, not just being a passenger, but actively flying an aircraft 35,000 ft in the sky. For a lot of people, that would be a dream-come-true. Unfortunately, most of us will never actually get the chance, but we can simulate it.

Aircraft simulators, or flight simulators, are anything that can replicate and reproduce the experience of flying an aircraft, from games to full-sized cockpits mounted on hydraulic actuators.

Simulators go all the way back to WWI. Wartime meant that pilots had to be trained en masse and quickly to fly and operate machine guns. In 1929, the Link Trainer, with a pneumatic motion platform capable of simulating pitch, roll, and yaw, was introduced. In 1948, Curtiss-Wright introduced the first complete simulator, with no visual displays or motion but an entire working cockpit. In 1954, General Precision Inc. introduced a motion simulator with 3 degrees. By 1982, the Rediffusion Company introduced simulators with seamless displays like we are used to today.

Now, there are different types of simulators to choose from. System trainers teach how to operate various systems, cockpit procedure trainers (CPT) teach crew checks and drills, full flight simulators (FFS) teach the use of motion in all six degrees of freedom, and part task trainers (PTT) teach simple avionics equipment usage that can be upgraded and compounded on. These different types of simulators also have many different uses.

In addition to training pilots to fly, flight simulators can be used to train flight crew personnel in normal and emergency flight operating procedures, crew and resource management, and threat and error management. Simulators aren’t just good for teaching and training, they’re also used to evaluate for errors and improvements, and test technical modifications before they’re implemented. Teaching flight crew how to deal with failures and malfunctions is crucial, but to do so in a real aircraft can not only be expensive, but dangerous. As a result, flight simulators are more preferable. They save time and money while increasing safety. Using even the most expensive simulator is still only 1/40th the cost of training in a real Boeing 747.

At Sourcing Streamlined, owned and operated by ASAP Semiconductor, we also want flight crews to be safe and prepared. So, as a premier distributor of aviation parts, we make sure to stock up on not only cockpits and actuators, but all kinds of flight actuators of the highest quality. Visit us at www.sourcingstreamlined.com to get started.


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Aviation inspection is very important as a preventable measure for minimizing potential problems. The inspection process eliminates the possibility of human error on the aircraft parts and components. Regular inspections include manual checks and visual examinations to determine the conditions of the components and aircraft parts. Maintaining the aircraft is critical to avoid any kind of failures that could be hazardous in causing an accident. The FAA, Federal Aviation Administration states regular inspecting acts as a preventative measure for maintaining and assuring “airworthiness”. The value of regularly inspecting provides a reduction in possible malfunctions, human error and operating failure because it detects minor defects and depletion at an early stage. This allows for the maintenance team to keep proper records logged to retain any history of issues that have occurred or may arise. There is also a very detailed preflight inspection which depends on aircraft and operations being conducted, this final inspection acts as a last-minute check prior to aircraft flying. In most cases, calendar inspections are common however inspections based on flight hours for scheduling is preferred.

The FAA provides guidelines for inspection of the aircraft, logbooks must be reviewed, and the entire maintenance record checked. This continuous procedure of being aware is essential in aircraft maintenance. The FAA also advises for numerous checklists which relate to each aircraft parts such as fuselage and hull, cabin and cockpit, engine and engine house, landing gear, wing and center section of aircraft, propellers, and much more. Each of these parts is checked for any possible failures and reporting of conditions. Applying each step and taking part in the due diligence of inspecting will mediate any possible issues or failures that may induce any complications.

Critical Safety Items (CSI) due to it relating to government contracts, demands more rigorous inspections because they relate to defense agencies and military services in the US. They are specific about any issues that could cause catastrophic failures, injury/death, or any accidental engine shutdowns.

Sourcing Streamlined, owned and operated by ASAP Semiconductor, should always be your first and only stop for all your hard to find or urgent aviation component needs. Sourcing streamline is the premier supplier of engine parts, aircraft landing gear and more! Whether new, old or hard to find, they can help you locate it. Sourcing streamline has a wide selection of parts to choose from and is fully equipped with a friendly staff, so you can always find what you’re looking for, at all hours of the day. If you’re interested in obtaining a quote, contact the sales department at sales@sourcingstreamlined.com or call +1 (763) 401-8616.


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