Parts is Parts!

July 6, 2007
Learning how to manage aircraft parts can make you more efficient and keep you out of hot water

The purchase, installation, and approval for return to service of the installed aircraft parts, combined with inspections, is the heart of the aircraft maintenance function. The regulations that govern replacement parts (short of FAR 43.10), have not changed appreciably since the conversion of all regulations from CAR to FAR as part of the Aviation Act of 1958.

FAR 43.10, “Disposition of life-limited aircraft parts,” was added as part of Amdt. 43-38, Eff. 4/15/2002 to clarify what a life-limited part is and provide some long needed instructions on how to handle them. In this article we will discuss parts and the handling of parts in detail, including life-limited parts.

What makes a usable part?

A usable part is one that has been through at least one FAA-approved quality assurance process and has successfully passed the inspection criteria of that process.

As a maintenance organization, certificated repair station, or individual, you are responsible for ensuring that all parts installed during maintenance meet the certification requirements of 14 CFR Part 21.303 “Replacement and modification parts.” Following are the five possible certification methods for NEW parts.

  1. PMA — Parts Manufacturing Approval applies only to specific part numbers and is usually associated with an STC or a direct replacement (non-OEM) part.
  2. PAH — Parts manufactured under the production certificate or the holder of the type certificate for that aircraft.
  3. TSO — Technical Standard Order applies to a specific FAA approved design. The organization manufacturing the TSO parts must hold TSO authorization from the FAA.
  4. Standard parts — Parts that are manufactured in accordance with an industry recognized standard such as AN, NAS, MS hardware and certain nonprogrammable electronic devices.
  5. Owner-produced parts — Parts produced by the aircraft owner (or his agent) for a specific purpose and for the repair of his aircraft. It is important to point out that owner produced parts are not exempt from FAA approval for complex fabrication.
    Although 14 CFR Part 21 addresses certification methods for new replacement parts, a certification method is also required for used parts. The certification of a used part is identified by its approval for return to service under 14 CFR Part 43 (Reference Part 43.13 and 43.9).

An approved vendor list

The first step is to develop a simple list of parts vendors that you have determined will send you approved parts when you order from them. Providing and enforcing such a list to your purchasing agent will ensure that only good parts are ordered in the first place, thus beginning the quality assurance process before the parts actually get to your doors.

Additionally, you should develop a procedure that enables the purchasing agent to approve and enlist a new vendor source. The best way is to develop a checklist and provide it to purchasing personnel to be used to help check out and verify a new vendor is worthy of being called approved. Then, follow through with close quality assurance inspection and verification when the part arrives. Set up a process by which vendors are placed on the list, audited regularly, and when necessary, removed from the list. It is a good idea to make a separate list and audit program for “outside service” vendors simply due to the difference in the type of regulations that service organizations are required to follow. An audit of service vendors will be quite different than one created for a parts supplier.

Types of suppliers

Anyone can sell you parts. At present, there is no regulation covering the sale of parts. Current rules regulate the installation of parts — not the sale of parts. This is why your company, as the parts installer, holds the responsibility of ensuring that the parts are approved. The best practice is to require your suppliers to include a statement of conformity with each order. A statement of conformity will help you hold the supplier liable; however, it will not eliminate your liability.

As a maintenance organization, you purchase parts to be installed on an aircraft in one of two distinct ways:

  1. Parts vendors — From a supplier or vendor who sells either new or used parts.
  2. Outside services vendors — From a supplier who actually repairs parts and returns them to you.

New parts do not have to come directly from the aircraft manufacturer; however, your supplier should be able to provide you with evidence (documentation) that the part has been through one of the five certification methods and made it through successfully. The documentation that you accept needs to be more than just a promise, it should include some concrete evidence from the FAA-approved manufacturer of the part.

In order to ensure that used parts are eligible for installation, we must make sure that they have “traceability.” What a word. Simply stated, the history of the parts must be traceable back to the most recent certification method. If it comes with a Part 43.9 maintenance sign-off from an agency that is properly qualified and authorized to certify the quality of the part, that is sufficient. A Part 43.9 sign-off is a proper 8130-3 or serviceable tag. Also, it just makes good business sense to establish solid long term relationships with good vendors.

Inventory management

Management of inventory is important in all types of business. When parts are purchased and not rotated out (sold), the unusable inventory becomes more of a liability than an asset. Even though it is on the books as an asset, your inventory can be tying up your liquid assets.

You may have heard the term just-in-time (JIT) inventories. This type of inventory management refers to purchasing the parts and materials so that you receive them “just-in-time” to use them right away. The whole philosophy is based around the truth that inventory that is sitting and not being moved is a bad use of the company dollars.

In the service business, JIT does not work as well — some say it does not work at all. Here, JIT inventory might mean getting the part just in time to put it on the airplane while the pilot is performing his pre-flight to leave the shop. Not good!

What we can do in the service business is learn from what we are moving, what parts are selling. We need to be able to capture the information as parts are sold, and then use that information to evaluate and plan purchases. Good data will help the parts manager order the supplies and materials that are used on a regular basis in volumes that make sense. Even then, there are always parts that come up that are not in stock and that need to be ordered — many times at the expense of higher freight and AOG charges. The goal is to plan well enough that the list of things we AOG is very small and the parts we stock are rotated through just about as fast as they are ordered. Develop a means of tracking what you sell and how often.


The receiving person, commonly called a receiving inspector, acts as a sentinel of sorts to prevent the entry of bad parts into your system. This job is very important and the person needs to be trained well in order to do a complete job in the receiving area. The receiving inspector must:

  • Check the content of a box with the packing list to verify that everything was included.
  • Check that the contents of the box were not damaged during shipping.
  • Verify that the part has with it the appropriate paperwork supporting its traceability.

If the receiving inspector finds something that is questionable, he or she needs to know what to do with the parts. It is a good idea to have an area set aside in or near the receiving area where these parts are placed in quarantine until a quality control manager can be brought in to help out.

Life-limited parts

Part 43.10, Disposition of Life-Limited Parts, speaks to this specific type of part. The regulation uses the following words to define life-limited parts. “Life-limited part means any part for which a mandatory replacement limit is specified in the type design, the Instructions for Continued Airworthiness, or the maintenance manual.” In other words, aircraft life-limited parts are those parts identified by the aircraft manufacturer or production certificate holder as having a total mandatory life limit of some increment counted in hours, cycles, landings, or by calendar.

The technician installing a life-limited part is responsible for, and should be held accountable for, recording all of the pertinent information regarding the life-limited part and its replacement in the appropriate maintenance records.

Receiving inspectors should pay particular attention to the type of life-limited parts that have a limited shelf life, or a limit to the period the material’s usability after its container’s seal has been broken (useful life).

Parts that have a specific shelf life — a limit as to how long they are eligible to be used — must be identified when they are received in some fashion to ensure that they are not used in the maintenance of aircraft after their expiration date.

Examples of shelf life-limited materials are adhesives, solvents, sealants, O-rings and other rubber products, and fire extinguisher squibs. Proper control over these items means purging them from the inventory before their shelf life has expired.

When these types of materials are received, they should be identified by the receiving inspector in an obvious way. Repair stations have many different ways of identifying shelf life-limited parts. One simple way might be to attach a brightly colored dot to the container and write the expiration date in the dot.

Limited useful life

Limited useful life items are those that must be used within a certain timeframe from when they are opened. Here, we need to mark the material when it is opened, not when it is received. The marking of these materials would then take place when they are taken from the parts store to the shop floor. The most effective procedure I have seen is to mark those material containers with a colored dot just like shelf life items, (using a different color dot) when they are received and then train the parts distribution personnel to mark the date in the dot when the material is checked out or removed from the parts store.

Materials lost in your toolbox

Items that have a specific shelf life must be removed from the production floor once their life has expired. A trap that is easy to fall into is to keep what is left over from one job for the next job. This usually results in a toolbox or cabinet full of half-used materials that have a life limit. A process should be in place that ensures the removal of these types of materials on a regular basis. Usually, someone from within the company will go around once a month or so and gather up all the old materials and dispose of them. Don’t forget about OSHA rules on the disposal of hazardous materials. It can be much more costly to be fined by OSHA for improper disposal of hazardous materials than to just pay to ensure proper disposal.

Traceability — After the fact

There will be a time when you will be asked to show the traceability for a part that you installed on an aircraft that has already left the facility.

Generally, company purchase orders (POs) are assigned a unique number and are filed in order by that number. This means that our parts purchase, storage and distribution system must be smart enough to know the purchase order for parts installed on a particular work order. We need to be able to go to the work order and from there identify each part that was installed on that aircraft for that visit and then identify the PO number for each of the parts installed. This is the cleanest type of traceability and is most desired. Often, once the part has been issued to the aircraft, there is no connection back to the purchase order. The best that many companies can do is show the last X-number of vendors that a particular part number was purchased from. In this case, direct traceability is non-existent but we can at least verify that the part was purchased from an approved source and that the PO includes appropriate certification evidence.

Aircraft interiors

Aircraft interior materials have a particularly unique traceability issue. When a lot of fabric or leather comes in for use, it must be burn tested or “certified” for usability in the aircraft. Many repair stations send pieces of these articles out for testing and certification. Maintaining a link between the material and the certification paperwork can sometimes be difficult. Once we start cutting up the material to be used, we no longer have the certification paperwork attached to it.

The best solution is to isolate the materials to be used for a particular aircraft and keep the certification paperwork for all of the material for that aircraft in a binder. That way, if there is ever a question regarding the burn certification for those materials, you can easily go to the binder and find the appropriate paperwork. It is also recommended that you provide a complete set of burn certification paperwork to the owner as well as keep your own copy in the work order package when the aircraft is approved for return to service.

Parts segregation and protection

The parts room should be separate from the maintenance shop work environment. FAR Part 145 requires that repair stations protect parts from contamination. “Each certificated repair station must provide: Space sufficient to segregate articles and materials stocked for installation from those articles undergoing maintenance, preventive maintenance, or alterations.” Proper protection also applies to the work being accomplished in the maintenance shop. “Each certificated repair station must provide: Sufficient work space and areas for the proper segregation and protection of articles during all maintenance, preventive maintenance, or alterations.”

It is important to cover opened areas of aircraft, engines, and components. The same holds true when using portable drills, grinders, and sanders. Machining tools such as drill presses, grinders and stationary sanders should be located in a back shop area if possible to reduce the possibility of contamination.

Parts tagging

Repair stations use a parts tagging system to ensure that parts are properly identified while in the repair station, and inform others as to the status of removed parts both inside and outside of the repair station. There are generally four types of repair station tags.

  1. Serviceable tag (or 8130-3)
  2. Repairable tag
  3. Unairworthy tag
  4. Identification tag

Serviceable tags are used to identify a part that is, of all things, “serviceable.” Two situations that create a part worthy of a serviceable tag:

  1. A part that has been removed from an aircraft but is known to be in fine shape with no discrepancies. Note: If the part is a life-limited part and its total used life is not known, the part must NOT be tagged as serviceable, but as unairworthy.
  2. The repair station has performed work on the part and the part is going to be returned to the customer instead of being installed on the aircraft (although many repair stations issue serviceable tags and also install the part).

The information on these tags should include at a minimum, the exact requirements found in FAR 43.9 since the serviceable tag is essentially a maintenance record entry. FAA Form 8130-3 has become an industry standard replacement for the old serviceable tag. Although Form 8130-3 began as an export document for Class II and Class III parts, repair stations are now authorized to use the updated document to approve for return to service following maintenance.

Repairable tags are attached to parts that have been removed from an aircraft and are in need of maintenance or repair before they can be re-installed. An example would be parts that have been removed and sent to an overhaul facility for overhaul. The basic information that should be on a repairable tag is the part description including part number and serial number, the reason the part was removed, and a description of the work needing to be done in order to make the part serviceable.

Unairworthy tags are used on parts that have reached their life limit or have been determined to be in need of repair or service and the repair or service that would need to be accomplished is not possible. The information to be placed upon the unairworthy tag is the part description, including part number and serial number, and the reason for removal. Unairworthy tags should only be issued by persons designated by the repair station as an authorized inspector.

The identification tag is used on parts that are not in need of repair or service, but are removed from the aircraft to facilitate other maintenance. Many times, a repair station will use an identification tag to identify a table or work bench that is being used to temporarily hold the disassembled parts of the aircraft. Identification tags do not require any specific signature or authorization but are primarily for the purpose of organization of parts removed.

Recording the maintenance

Once work is completed, one of the most critical steps in the process is the generation of the entry for the maintenance logbooks. The reason the logbook entry is important is more than just the fact that it is required by regulation. The aircraft logbook is the place that history of maintenance and inspections performed is permanently kept. What this means is that if you forgot to write it down, essentially it did not get done. The evidence of completion of the work is the mechanic’s signature in the logbook with a description of the work accomplished. FAR 43.9 contains the required content for entries made upon completion of maintenance and should be referred to for guidance.

Maintenance record requirements are found in FAR 91.417. This is where we find the details of the maintenance history that the owner of the aircraft is expected to be able to produce when asked by the FAA or a prospective buyer. The requirements of FAR 43.9 and 43.11 are a little vague unless you understand the desired result, found in 91.417.

A maintenance logbook entry needs to be easy to read. Most are created now using a computer and in doing so, we should take advantage of all the tools that are available such as sorting the items that were accomplished in a way that makes sense. The content needs to be clear and concise. When replacing a part, the entry should clearly state what part number was installed and if the part is serialized, what serial number was removed in addition to the serial number installed. Reference should always be made to any work performed by another agency even if it is only by reference to the other agency’s serviceable tag.

Using these guidelines as a framework will help you build a parts management process that will ensure the efficient use of approved parts as well as to develop satisfied customers. The evolution of the maintenance organization from the two-man shop to the 1,200+ person certified repair station has many stages, but these basics apply regardless of shop size.

Joe Hertzler is the CEO and co-founder of Avtrak Inc., provider of the industry’s first Internet-based and compliance-focused maintenance tracking service — Avtrak GlobalNet. Avtrak has announced, within the past two years, alliances with Gulfstream, Raytheon, and Sikorsky that have each selected Avtrak’s GlobalNet technology for the next generation of their factory-provided maintenance tracking services, Gulfstream, Raytheon FACTS, and Sikorsky Helotrac II.