Understanding Expendable Parts: A Comprehensive Guide

There are a number of different classifications of parts in the aircraft maintenance cycle that we have talked about over the course of our blog, from rotable parts to general aircraft parts procurement and logistics. In aviation maintenance, one of the more important types of aircraft parts are expendable parts. 

Expendable parts make up a pretty significant amount of the replacement parts used in aircraft maintenance and repair. These include all kinds of different part types like:

  • Gaskets
  • Seals
  • Bolts, washers, and assorted hardware

Any aircraft part that is disposed of after use rather than rebuilt, which is a lot. 

Let’s take a look at expendable parts, what XB3 means to the military aircraft maintenance mission, and a lot more. 

Definition and Classification of Expendable Parts

First off, let’s talk about the definitions and different classifications of expendable and consumable parts. There are a few different primary or core types of expendable parts that common to aircraft. 

Consumable Parts

Here are the three most common consumable part categories:

  1. Lubricants and oils. This one is pretty obvious, but it is a core category. All greases, hydraulic fluids, and, in certain applications (bombers and some fighters), cooling oils.
  2. Chemicals: chemicals are used all over the aircraft and are always classified as consumables. These commonly include adhesives, sealants, and de-icers. 
  3. Gaskets and seals are an entire category and are replaced routinely throughout all phases of maintenance. For example, every time a pump is removed or replaced, the gaskets have to be replaced, and this happens all the time. 
  4. O-rings and washers: While small in size, the importance of these can’t be overstated. The average military aircraft uses hundreds, if not thousands, of O-rings and washers to seal all kinds of parts. These are especially common on drain plugs used on accessory gear drive boxes, hydraulic pumps, and fluid filters (Delta-Ps). 

Fasteners

Fasteners are one most important expendable parts in the supply system. They are important for the overall airframe, along with individual aviation components. 

  1. Bolts and screws: it is extremely common for fastens to require replacement during all phases of maintenance. The heads get rounded or stripped, and threads are easily crossed or just destroyed in general. Replacing fasteners during maintenance is cheap insurance to ensure it is easy to remove the next time instead of leaving a problem for the next maintainer. 
  2. Nuts and rivets: while not the same thing, the same rules apply. Nuts get corroded, stripped out, and generally abused, so replacing them outright is good practice when they are removed for maintenance or repairs. Rivets are a one-time-use consumable part used in all aviation applications, so a good stock of rivets of all common kinds needs to be kept in bench stock. 
  3. Pins and clips: these are some of the most simple and basic maintenance materials commonly used. Clips and pins are used all over the aircraft to secure fasteners, especially in applciaitons like castle nuts, where the nuts is not held on by a high torque value but is instead relatively loose and held in place by a pin. Pins should discarded after one use, so they are a bench stock must-have. 

Filters

We talked about this briefly, but filters are a category consumable that is critically important for a bunch of different areas of the aircraft, particularly the powerplant and hydraulic systems. Filters are replaced at standard intervals for several different primary components.

Hydraulic systems use filters to extend the life of the components and the fluid. Engines and APUs are heavily reliant on consumable filters to maintain a high level of reliability, and again, filters = cheap insurance. Dirty or contaminated oil is the quickest way to destroy a multi-million engine short of FODding it out. 

Characteristics and Life Cycle of Expendable Parts

There are a few more categories of expendable parts that are used for the standard servicing of both aircraft and component materials, but those that we talked about are definitely the most common. 

What about their life cycles, though? It is important to understand the anticipated lifecycle of expendable parts. 

Understanding the Life Cycle

It is impossible to put a single figure to this because it varies so widely depending on application and the area of the aircraft that the consumables come from. 

For example, tires have a general life expectancy of anywhere 300-500 landings but this varies considerably. Asphalt runways and Portland Concrete Cement (PCC) runways have substantially different wear characteristics, and predominantly coral runways (found in the pacific) substantially increase the wear rates. 

Brake pads are similar in terms of variation. A good rule of thumb is anywhere from 500 -2,000 braking cycles, but this is almost impossible to accurately predict. For flight safety, brake wear indicators are checked during every throughflight, postflight, and preflight inspection. This is even more difficult to predict because it relies heavily on the tendencies of each pilot, whether the aircraft has thrust reversing capabilities or a drag chute, and especially average runway length. If the home station for the aircraft uses a long runway, brake wear should be less than at a station with shorter runways.  

Applications of Expendable Parts

Consumable parts are used all over every aircraft and are almost too numerous to mention. 

Every light bulb, fuse, relay, and a good number of switches are consumable parts. Batteries are another essential piece of equipment that needs to be replaced on regular cycles before failing (at least, that’s the idea). 

Importance in Aircraft Maintenance

With so many consumables, it’s easy to understand how they play a critical role in not only overall maintenance but also flight safety in general. 

Consumable filters keep all kinds of nasty little contaminants from getting into the engines through fuel, oil, and hydraulic systems. Keeping lubricants clean is imperative for the longevity and overall effectiveness of the fluid, which translates to the longevity of the component as a whole.  

Managing Expendable Parts

So, how can you manage your expendable parts?

Most expendable parts are kept in bench stock, although not exclusively. This is due to their high consumption and common demand. Of course, this doesn’t apply to large consumables like tires, brakes, and batteries. But gaskets, hardware, fuses, adhesives, and sealants are routinely kept in bench stock for ease of access. 

Since consumable parts are so common and used often, keeping a strong supply of them is critical. Even though they are simple, a missing or defective O-ring or gasket will red X an aircraft instantly. Sometimes, the smallest parts can have the biggest impact on aircraft. 

Supply Chain and Inventory Management

Greenwood Aerospace is the supply chain and inventory management specialist you need to partner with for all of your consumable demands. We have spent over forty years setting up reliable partnerships with industry leaders to source consumable and expendable parts for your military aircraft mission. 

We have the capability to establish supply chains and even warehouse your parts on demand. 

Final Thoughts

Consumable aircraft parts are one of the most critical categories of aircraft parts, even though a lot of them don’t look like much. O-rings and gaskets cost cents but can and will ground an airplane if they fail. 

Greenwood Aerospace will make sure you don’t end up grounded because of consumable parts issues. We have the connections to get you the parts that you need. Give us a call at (580) 762-2580 to see what we can do for you, or if you know what you need, start an online quote right now!