Aircraft taxiing is a complex procedure, often involving multiple aircraft that are taking off, landing, loading passengers, and delivering them to their destination. It is important that there is safe and efficient movement of all aircraft throughout the aerodrome, and a means of aircraft being able to travel from the gate to the takeoff point. Many aircraft do not have the ability to even reverse, making movement from the gate near impossible. To solve this, a procedure known as pushback is used and is conducted by aircraft tugs.

An aircraft tug, or a pushback tractor, is a low profile vehicle that is able to fit under the nose of an aircraft and provides for the movement of aircraft from the gate. Even if an aircraft has the ability to reverse, there poses many issues with using it. Aircraft power is created by the engines, which in turn creates thrust. If this was used at the gate for reversing, it could pose a serious risk for personnel around the engine, possibly damage equipment and the gate, and cost a great amount of fuel. Using thrust at such a low speed for reverse could even damage the engine, creating another reason to not use such a method. With aircraft tugs, any aircraft can be safely and optimally moved around as needed anywhere in the aerodrome.

Aircraft tugs have multiple ways that they can be attached to an aircraft, and some of these include bypass pins that are installed into the nose gear, or by using a towbarless tractor which lifts the nose of the aircraft and tows it around. Israel Aerospace Industries has even designed a semi-robotic tug called TaxiBot which is controlled by the pilot and allows for quick and efficient taxiing to the takeoff point. This makes it so that the engine does not even need to be turned on until shortly before takeoff, saving a great amount of fuel. As pilots have poor reverse visibility, and reversing with the aircraft can prove to be dangerous or impossible, aircraft tugs prove to be an invaluable asset to aircraft taxiing.

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If you’re a frequent flier, then you’ve likely been on a variety of different aircraft, from small and cramped, to cramped and complex. Smaller aircraft are often less spacious with only two rows of seating, whereas larger aircraft typically have two or more rows of seating. However, the most significant difference between different aircraft is not the size of the aircraft, but the weight. The weight is especially crucial for pilots because they need certain ratings to be able to fly bigger aircraft. For both air traffic controllers and pilots, the categories are crucial in notifying pilots of dangerous conditions in the wake of heavy planes. For a more detailed description of the differences between large and heavy aircraft, read on below.

  • Maximum Takeoff Weight

A large aircraft is defined by the Federal Aviation Administration as one that has a maximum certificated takeoff weight (MTOW) that's more than 41,000 pounds and less than 300,000 pounds. This means that the aircraft is able to take off into flight at that weight range (41,000 lbs fewer would still be considered “large”). In regards to the MTOW of a heavy aircraft, the aircraft has to be 300,000 pounds or more. A medium aircraft has an MTOW that's 12,501 to 41,000 pounds. A small aircraft is one with an MTOW of 12,500 pounds or less.

  • Super Aircraft

The FAA recognizes two different types of very weighty aircraft and identifies them as being extra hazardous for another aircraft to fly behind. These types of aircraft, which are the Ukraine-built Antonov An-225 and the Airbus A380-800, are identified as super aircraft. The former has an MTOW of 1.41 million pounds and the latter has MTOW of 1.27 million pounds.

  • Pilot Certification

Pilots must have specific ratings in order to legally fly turbo powered or large aircraft. The rating can be obtained by passing a practical test called a checkride. On the checkride, the pilot must operate on a highly realistic simulator or an actual airplane, this test of which is preceded by months of training and instruction.

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Minimizing aircraft downtime and exploiting aftermarket opportunities are quickly becoming more of an important focus to Maintenance, Repair, and Overhaul divisions of aircraft companies throughout the years. Aircraft Health Monitoring Systems, or AHMS, are proving to be a promising business opportunity for OEMs and airlines as a way to enhance aircraft safety due to their ability of real-time data captured through sensors that are integrated on aviation parts. AHMS can also optimize company MRO costs by utilizing non-invasive inspections and testing that report on aircraft conditions. Through 2019 and beyond, there are a handful of industry-wide activities that will continue to develop the AHMS market.

One way in which the AHMS market is developing is through stakeholders in aerospace that are working with universities to explore technologies that enable them to precisely monitor aircraft health. Stakeholders are utilizing academia and start up companies as they are interested in the ability to detect flaws in coatings, surfaces, and materials. These detections will aid in sectors such as quality control, structural health, maintenance assurance, and product safety. Photonics to monitor conditions in real-time, structural health, and vibration of the aircraft and its components are also disruptive innovations that aircraft manufacturers and aircraft components suppliers are interested in for being implemented into future AHMS technologies.

Manufacturers are also looking to utilize open data platforms as a way to standardize the approach for AHMS across their global fleets. Corporations such as Airbus plan to evolve their data platform, Skywise, for it’s operators as an end-to-end health management solution. Airbus Customer Service digital suite and Airbus flight operations and maintenance exchanger tool would gain accessibility through this platform.

AHMS continues to promise growing opportunities for service providers working in the aviation vertical by increasing the aerospace involvement of Engineering Service providers. When aircraft near the end of their life, they warrant a significant amount of MRO investment before they are able to fly regularly as well as need intensive checks in-between flights. OEMs are searching for a way to revamp old aircraft to improve their functionality and AHMS provides propositions to these service providers as a solution.

Along with these activities and more, AHMS can create quicker maintenance operations and reduce the downtime of aircraft for next generation predictive analytics algorithms, as well as join various cross vertical services pertaining to chemical materials, mechanical and structural engineering, and information and communication technologies. AHMS provides a solution and opportunity as fuel prices continue to rise and machine learning methods evolve, creating an interest for manufacturers that are searching for aftermarket services.

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To explain the federal supply classification system, we must first understand what a National Stock Number is. National Stock Numbers or NSNs, are 13-digit serial numbers assigned to all standardized items within the federal supply chain. All components that are used by the U.S Department of Defense are required to have an NSN, the purpose of which is to provide a standardized language of naming components. Also known as NATO stock numbers, NSNs are recognized by all NATO countries. NSNs are assigned by the Defense Logistics Agency  and are typically in the format XXXX-XX-XXXXXXX.

NSN are  broken down into smaller subcategories, each providing individual information about the component. To begin, the first four digits of the NSN are known as the Federal Supply Classification Group. The FSCG determines which of the 645 subclasses an item belongs to. The FSCG is further split into the Federal Supply Group (FSG) and the Federal Supply Classification (FSC). The FSG is made up of the first two digits of the NSN which determines which of the 78 groups an item belongs to. The second 2 digits make up the FSC, which determines the subclass an item belongs to.

In the aerospace industry a key federal supply group is FSG 15: Aircraft and Airframe Structural Components. The Department of Defense produces a cataloging handbook known as the H2, which lists all the current federal supply groups and their subclasses. It is a handy reference guide for the classification of any NSN. Fixed wing components for use on aircraft are found under Federal Supply Group 15 and Federal Supply Class 10. If you are looking at a seemingly incomprehensible list of NSNs, you can simply look at the first four digits and you will at least know what commodity area the item belongs to.

The remaining 9 digits of the NSN are made up of the 2-digit country identifier followed by the 7 National Item Identification Number (NIIN). The US for example,  has the country identifier, 00. Unlike the FSCG, the NIIN is unique to the item itself.

The federal supply classification system is designed to help make the parts supply chain more accessible and uniform. Without FSGs, FSCs, or NSNs, it would be difficult for manufacturers and suppliers to determine what exactly they were buying and selling. A common place hardware components, manufactured in the millions, may be called one thing by one manufacturer, while having an entirely different name somewhere else. This is why the DoD moved to implement a complete naming and classification system. 

At ASAP Distribution, owned and operated by ASAP Semiconductor, we have a wide-ranging list of NSNs, FSCs, and FSGs  for you to source parts from. Our helpful search engine lets you type in the exact NSN you need. As a premier supplier of parts for the aerospace and defense industries, we’re always available and ready to help you find all the parts you need. For a quick and competitive quote, email us at or call us at +1-702-919-1616.

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The magnetic compass is the most common device found in the pilot’s cockpit; however, it is also known as the faultiest device. During times of turbulence, the compass can become increasingly difficult to read and be subject to incorrect acceleration and turning errors. Its inaccuracies can make it difficult for the pilot to fly by safely. To come to the rescue of frustrated pilots, the Heading Indicator (HI) is a gyroscopic instrument that maintains alignment with the magnetic compass. This tool makes for more accurate flight paths by eliminating severe acceleration or turning errors.

There are a few mechanical factors, mainly attributed to friction, that may cause the HI to drift off the original alignment with magnetic north. This is referred to as mechanical drift. The rotation of the earth can also affect the HI. If you imagine a line running north in space it will forever be changing because of Earth’s constant rotation. This is referred to as apparent drift.

However, these errors can be fixed with a simple solution. The HI is able to be realigned to the magnetic compass found in all aircrafts when corrections need to be made. The pilot should be sure to check the power source is active and that the correct turns are being indicated on the HI prior to entering air travel. Every HI has a “slaving knob” that enables the pilot to realign the HI, correcting for both the mechanical and apparent drift. This should be made a routine alignment by the pilot every 10-15 minutes.

Here are some tips to manually align the HI with the magnetic compass if these errors occur: First, choose a reference point directly ahead of the plane, aim on that point, and fly steady and straight. Maintain the plane’s heading toward this reference point and adjust the HI to match the magnetic compass readings. Ensure that the plane has remained steady and straight on its heading toward the reference to finish the realigning process.

With the use of these flight instruments in conjunction with one another, pilots should experience a more reliable tool to help them accurately navigate the sky.

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Landing gear is a critical component for any aircraft, as it allows the aircraft to takeoff, land, and taxi safely on the ground. However, the way landing gear is designed and arranged on the aircraft can affect its weight distribution, center of gravity, and handling characteristics on the ground. Most modern civilian small aircraft are built in either the tricycle or tailwheel configurations.

In the tricycle configuration, two main wheels are located on either side of the fuselage, with a third wheel directly underneath the nose. This configuration is identical to the children’s toy, thus giving it the name. Tricycle landing gear has three main advantages: firstly, it allows for more forceful application of the brakes during landings at high speed, gives the pilot better visibility during takeoff, landing, and taxiing, and helps prevent ground looping or swerving while taxiing. This is because the aircraft’s center of gravity is forward of the main wheels, keeping it moving in a straight line rather than wavering.

Tailwheel landing gear also has two wheels on either side of the fuselage attached ahead of the aircraft’s center of gravity, which support most of the aircraft’s weight on the ground. A third wheel is placed in the rear of the fuselage directly under the tail, thus giving the configuration its name. This arrangement means that the plane is slightly tilted back when on the ground and has all three wheels on the ground, which provides greater clearance between the aircraft propeller and the ground. This in turn means that a larger propeller can be installed on the aircraft, and allows it to operate from rougher, unimproved airfields. However, with the center of gravity located behind the main landing gear, directional control of the aircraft is more difficult, as it is more likely to swerve during taxiing. The lack of forward visibility while the tailwheel is on the ground is also a major issue, and one that requires specific training for the pilot to adapt to.

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There are two main approaches to the construction of the outer shell of an aircraft fuselage: monocoque and semimonocoque. Monocoque systems were employed in early aviation, starting in 1918, but semimonocoque methods are the most widely seen approach in modern aviation. The main differences between the two approaches is in their designated support structures.

Monocoque is a French term that means “single shell”. Similar to the concept of the surface of an aluminum can, the fuselage is wrapped in a layer of stressed aluminum alloy. The monocoque system does not have a second support structure behind its outer layer, so it is completely dependent on the construction of the outer layer to distribute stress and load. To add strength to the skin of the fuselage, it is sometimes fortified with stiffeners. This approach becomes very strong, as twisting and bending stresses can be distributed through the external skin. However, this method is not tolerant to any type of surface corrosion or deformation. When stiffeners are added, it increases the weight of the monocoque. As such, monocoque approaches have been widely phased out in favor of semimonocoque structures. Automobiles still use the monocoque approach, and some smaller aircraft, such as helicopters. This is because a one-layer system allows for more space in the interior of an aircraft.

Semimonocoque methods utilize part of monocoque technology, as the name suggests, but add a partial “inner skeleton”. It is essentially a dual layered construction. A semimonocoque fuselage uses a substructure that consists of bulkheads and formers which reinforce an outer skin layer. The second layer of support reinforces the outermost layer by assuming part of the applied load, therefore stress is evenly distributed across the fuselage. Due to the extra layer of support, the fuselage shape is able to stay intact, and has better longevity than a monocoque approach.

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Have you ever wondered how air conditioning works on a commercial aircraft? Air cycle air conditioning is the most widely used process in commercial aviation. This system uses engine bleed air to pressurize the aircraft cabin. By manipulating bleed air through a few important components, this system is able to provide comfortable air flow to the cabin during flight.

Bleed air is too hot to pump directly from the engine system into the cabin. In order for the incoming air to begin the cooling process, it is routed into a primary heat exchanger, which reduces the temperature of the air by ducting controlled ram air through the exchanger. Ram air is provided by the aircraft pneumatic system.

The cooled air is then directed into an air cycle machine (ACM), or refrigeration unit, where it is compressed before flowing to a secondary heat exchange. The secondary exchanger works the same as the primary, and air is mixed with more ram air and cooled further. Meanwhile, excess cool air is fed from the secondary exchanger back to the ACM, where it drives the expansion turbine and cools the unit.

 As the temperature of the air changes, air molecules cannot hold as much water as before. A fiberglass water separator is necessary to remove water from the air flow before it enters the cabin. Lastly, air at the proper temperature adjustment is delivered to the cabin through an air distribution system.

It is worth mentioning the following component parts, as they are integral to the air cycle process: a pack valve, bleed air bypass, and refrigeration turbine unit (ACM). A pack valve serves the same function as a supply shut off valve. It regulates pressurized bleed air entering the system and can open or close depending on the needed air flow. This part also operates as a redundancy measure for overheating and will shut off air supply if necessary. A bleed air bypass removes some pneumatic air and mixes it with cold air so that air enters the cabin at a comfortable temperature. The bypass is controlled by an auto temperature controller.

A refrigeration turbine unit, also referred to as an ACM, is the main cooling system. It is essentially a compressor that is driven by a turbine. Air from the primary heat exchanger flows to the compressor area of the unit. The air is then sent to the secondary heat exchanger for a second cooling process. The highly pressurized air allows for an easier exchange of heat energy when mixed with ram air. Excess cooled air is then directed from the secondary heat exchanger to the ACM to cool the turbine.

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Among the various types of aircraft landing gear, all are currently sorted into two main categories: fixed and retractable. Fixed landing gear simply refers to gear that is permanently attached to the airframe. Retractable landing gear refers to a system that allows landing gear to be extended and retracted from the aircraft as needed. The use of both arrangements primarily relies on aircraft speed and internal volume.

If you regularly fly on commercial airlines, you are likely familiar with retractable landing gear to some degree. This configuration is the most commonly used setup on standard commercial aircraft. Large aircraft retraction systems customarily rely on hydraulics for operation. A landing gear parts supplier, and/or a landing gear parts distributor, can expect to encounter conventional hydraulic systems components. These include, but are not limited to priority valves, actuating cylinders, and selector valves. Another vital part in the retractable gear layout is the gear door. Gear door operations and arrangements vary by aircraft. Most arrangements retract the landing gear into the fuselage, if there is space. This is typical in aircraft such as the Boeing 747 and Airbus A340. If space is not available, extra space is built extending from the fuselage.

Though the retractable configuration is the most common among commercial aircraft, fixed landing gear is still in production. It is most frequently seen on relatively small, light-weight, single engine aircraft. On occasion, it is also seen in light-weight twin engine planes. In a fixed arrangement, the landing gear parts are attached to the airframe, which exposes it to the slipstream in flight. This creates what is referred to as parasite drag. This occurs due to the extension of the landing mechanics outside of the airframe. As long as the aircraft is relatively slow, it will benefit more from having a fixed landing gear system. This is due to the fact that retractable landing parts are quite heavy. Induced drag is drag created simply due to the added weight of retractable landing gear parts. Overall, in order for fixed landing gear to be more beneficial to an aircraft, the potential parasite drag must amount to less than the potential induced drag of retractable mechanisms.

Landing gear arrangements have changed drastically over time. Leonardo Da Vinci is believed to be one of the first conceptualize a formal landing gear system for his “flying machines”. Fast forward to the 1920’s, fixed landing gear was positioned, statically, under the fuselage. It was not until 1927, that research found a considerable amount of fuselage drag was contributed by fixed landing gear. Aircraft enthusiasts might also be familiar with the 1930’s Boeing Monomail, which is one of the first planes credited with the initiation of retractable landing gear. Nearing a century after the birth of commercialized retractable landing gear, both fixed and retractable forms are still in use.

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An aircraft actuator is a type of motor that moves mechanisms and systems using hydraulic fluids and currents. They produce linear, rotary, or oscillatory motions. Actuators have applications in many fields and can be used in many kinds of machinery. Many of our common household items, such as printers and disk drives, have actuators. They can even be found in cars! But, because they have so many uses, and each is subject to its own specific conditions, there are considerations to be had when deciding on which actuator to use. The four main types are:

  • Hydraulic actuators require a cylinder which applies hydraulic power to start the mechanical routine. It takes more time to gain speed and slow down because liquids are incompressible. The hydraulic actuator can also be operated manually, like a hydraulic car jack .

  • Pneumatic actuators are very similar; however, they use compressed gas instead of liquid. The compressed gas is moved into a linear or circular motion, depending on the type. The pneumatic actuator is used more in main engine controls because it exhibits a quicker start and stop from the source. It is also used in projects where cleanliness is a priority, because unlike the hydraulic actuator the gas will no spew liquids or spill. However, this type of actuator is generally larger and louder.

  • Electric actuators convert electricity into torque. This actuator is used to create motion for machines that require multiple valves, such as gate or globe valves. Electric actuators are often installed into engines, where the actuators open and close the valves. This is also another relatively clean option because it does not require any fluids.

  • Mechanical actuators convert the circular motion into linear motion. This type of actuator is commonly used in larger sized machines. Devices like rails and pulleys are used in order to convert the motion.

ASAP Distribution, owned and operated by ASAP Semiconductor, should always be your first and only stop for all your hard-to-find actuator. ASAP Distribution is the premier supplier of hydraulic actuators, pneumatic actuators, electric actuators, mechanical actuators, and more! Whether new or obsolete, we can help you find all the parts you need. ASAP Distribution has a wide selection of parts to choose from and our dedicated staff are available and ready to help 24/7x365. If you’re interested in a quote, email us at or call us at +1-702-919-1616.

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