What Are Rotable Parts and How to Manage Them

This is the second in our series on rotable aircraft parts. A few different types of parts are commonly used in the aviation maintenance industry, and rotable parts are among the most important parts on aircraft. 

So, what is a rotable part, and why are they so important? Let’s take a look at rotable parts, what they mean for your military or government mission, and how you can manage them. 

Rotable Vs. Repairable Aircraft Parts

There is some confusion about whether or not rotable parts and rebuildable parts are the same thing.

Rotables and repairables are not the same thing. 

Here are some of the distinctions between aerospace rotables and repairable parts:

  • Aircraft rotable parts are the components of an aircraft (fixed or rotary-wing) that are intended to be removed at certain, specified periods of time and then rebuilt and reinstalled on the same aircraft or a like aircraft. 
  • Generally speaking, rotable parts are critical to safe and reliable flight operations. 
  • A few of the common rotables are some text
    • APUs
    • Engines
    • Gearboxes 
    • Avionics
    • And a lot more
  • Rotable parts are often managed through exchange programs where air carriers work with MROs and other repair facilities to swap out parts due for rebuild. In return, they will get a fresh rotable unit to install on the aircraft. 

By contrast, repairable parts

  • Repairable parts are rebuilt upon becoming unserviceable. These are not necessarily rotable items, although rotable parts are usually repairable. 
  • Repairable parts undergo maintenance and repairs to restore them to a serviceable condition. 
  • The big difference is that repairable parts are not necessarily those with a specific timeframe for replacement like rotable parts, but they are able to be repaired and placed back in inventory. 

A wheel is one of the best examples of a repairable part. It has to be inspected and often repaired whenever a tire is replaced. However, it is not rotable because there are no mandatory replacement cycles for tires and wheels.  

What Are Some Rotable Parts Aircraft Examples?

The best examples of rotables are the engines. Engines must be taken off and fully inspected at intervals. Generally, an identical engine is put on the aircraft out of the rotable stock during this time. Then, the removed engine will go back into the inventory pipeline after it is inspected. 

Engines also have overhaul cycles, so no matter how well the engine operates, it must be removed and fully overhauled. 

The other more common rotable items are APUs, parts of the avionics suite, hydraulic actuators, and parts of the landing gear assembly. 

How Are Rotables Different From Other Spare Parts?

Rotable parts and spare parts are similar but not exactly the same thing. Spare parts may or may not be repaired, as well as repairable parts. A lot of spare parts and what are known as expendable or XB3 parts. 

Spare parts are parts that are expected to be used, i.e., high-use items that routinely need to be replaced. Tires are a common spare part, and they are also a hybrid because, in military circles, there are two items with every tire issued: 

  1. The tire is a spare part and is sort of expendable (if it hasn’t been capped, it is turned in for a recap). 
  2. The wheel is a rebuildable part unless damaged beyond repair. Depending on the aircraft, it may be rotable (all aircraft in the military inventory have different requirements).

Windows and windscreens are another good example of spare parts that are not rotable or repairable. When the window or windscreen is damaged or delaminated beyond limits, it must be replaced and discarded. 

Examples of Airframe Rotable Parts

So, what are some of the most common airframe rotable parts? 

Let’s take a look. 

Line Replacement Units

According to MIL-PRF-49506:

“An LRU is an essential support item that is removed and replaced at the field level to restore the end item to an operational-ready condition. Conversely, a non-LRU is a part, component, or assembly used in the repair of an LRU / LLRU when the LRU has failed and has been removed from the end item for repair.”

What does this mean? 

An LRU (and the other similar downstream items) are built to specifications so that multiple manufacturers can build them to the same specifications. Avionics boxes are some of the most common LRUs, so keeping them available is important. 

Greenwood is not only your procurement expert for LRUs, but we can also warehouse them for you and package them in accordance with all MIL-SPEC guidance. 

Engines

The engines are another primary rotable part. They are designed to be easily and quickly removed from the aircraft and transported to a repair facility. Usually, the replacement unit can be installed in a shift, assuming there is no damage to the fire detection loop or any other pylon parts.

When an engine is pulled from an aircraft for detailed inspections or an overhaul, it won’t necessarily go back on the same aircraft. But that doesn’t matter; it is compatible with any other aircraft of the same MDS, so it can go into the supply chain once it is inspected or overhauled. 

Auxiliary Power Units

A close cousin to engines is the auxiliary power unit (APU). These are nothing more than a very small turbine engine that provides two things for the aircraft:

  1. Electrical power through an attached generator.
  2. Bleed air for engine starts.
  3. On some aircraft (the B-1B, for example), they are also in line with the hydraulic pumps, so the APUs actuate airframe components like the rudder, stabs, flaps and slats, etc. 

An APU is another rotable part that must be removed for inspection at regular intervals and repaired or overhauled. 

While much smaller than an engine, APUs must be packaged and shipped according to MIL-SPEC packaging requirements. Greenwood Aerospace is your trusted expert in MIL-SPEC packaging and aviation logistics. 

Can You Lease Rotable Aircraft Parts?

Finally, can you lease out rotable parts?

This is really something more aligned with commercial air carriers, as different rules govern military aircraft supply chains and are not used for profit. But for the civilian aviation markets, yes, rotables can absolutely be leased. It is very prudent for a commercial air carrier to lease out their supply of engines rather than just having them sitting in storage, especially if they have a surplus of engines or LRUs but not enough to sell. 

Greenwood Aerospace Is Your Answer

Greenwood Aero has been in the business of procuring parts, storing parts, and handling military and government aircraft logistics for over four decades. We know the market and have forged relationships with the best parts suppliers and MROs in the business, saving you a ton of time and money. 

If you are ready to start saving time and money procuring rotables or any other parts for your supply chain, give us a call, and one of our seasoned specialists will get you set up!