What makes a part airworthy?

Parts is Parts

What makes an aircraft part airworthy?

Joe Hertzler

The purchase, installation, and approval for return to service of installed aircraft parts, combined with inspection of those parts as a whole, makes up the aircraft maintenance function. The regulations that govern the approval of new replacement parts can be found in CFR Part 21. Part 21 establishes the quality standard for the manufacturing of new replacement parts. (Used parts will be addressed separately later in this issue.)

Approval of new parts
An approved part is one that has been manufactured as part of an FAA-approved quality assurance process (quality standard) and successfully passed the inspection criteria.

As a maintenance organization, certificated repair station, or otherwise, you are responsible for ensuring that all new parts installed during the maintenance function have been manufactured to one of the quality standards of 14 CFR Part 21.303. Following are the five possible quality standards for new parts.

PMA - (Parts Manufacturing Approval) Applies only to specific part numbers and is usually associated with STC or a direct replacement (non-OEM) part.
PAH - Parts produced under a type or production certificate.
TSO - (Technical Standard Order) Applies to a specific FAA-approved design. The organization manufacturing the TSO parts must hold TSO authorization from the FAA.
Standard parts - Parts that are manufactured in accordance with an industry recognized standard such as AN, NAS, MS hardware and certain non-programmable electronic devices.
Owner-produced parts - Parts produced by the aircraft owner (or the agent) for a specific purpose and for the repair of his or her aircraft.

Note: Owner-produced parts are not exempt from FAA approval for complex fabrication.

Approval of used parts
Although 14 CFR Part 21 addresses new replacement parts, a quality standard is required regardless of whether the part is new or used. The quality 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).

Proper approval for return to service is most commonly in the form of an FAA form 8130-3. The part can be overhauled, repaired, removed-serviceable, etc. Be sure that any used parts are coming from a reliable source along with proper documentation. Keep that data on file as well as provide it to the customer.

Develop an approved vendor list
Develop a simple list of vendors that you have determined will supply approved parts. This will ensure that only approved parts are ordered, thus beginning the quality assurance process before the parts actually get to you.

Additionally, you should provide a procedure that enables the purchasing agents to enlist a new vendor source when they come across one. Develop a checklist of key questions and concerns and provide it to purchasing to help evaluate a new vendor. Then, follow through with detailed quality assurance inspection and verification when the part arrives. Establish a procedure by which vendors are 1) placed on the list, 2) audited regularly, and if necessary, 3) removed from the list. It's also a good idea to make a separate list and audit program for outside service vendors due to the different regulations that organizations are required to follow. An audit of service vendors can be quite different than one for a parts supplier.

Different types of suppliers
Anyone can sell parts. At present, there is no regulation covering the sale of parts. Current rules only regulate parts manufacturing and installation. This is why your company, as the parts installer, holds the responsibility of ensuring that the parts are approved. It is a good practice to require your suppliers to include a statement of conformity with each order. It will help you hold the supplier liable, but will not eliminate your liability.

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

  1. From a supplier or vendor who sells new or used parts.
  2. From a supplier who actually repairs parts and returns them to you.

New parts don't have to come directly from the aircraft manufacturer; however, your supplier should be able to provide evidence (documentation) that the part has passed a quality inspection. 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, 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. If it comes with a 14 CFR Part 43.9 sign-off from an agency that is properly qualified and authorized to make the "quality determination," that is sufficient. A 14 CFR Part 43.9 sign-off is a proper 8130-3 or serviceable tag.

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

The receiving inspector must:

  • Check the contents with the packing list to verify that everything was included.
  • Check that the contents 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, it is a good idea to have a section set aside in the receiving area where these parts can be placed in quarantine until the quality control manager is available to resolve the matter.

Life-limited parts and materials
Aircraft life-limited parts are those parts identified by the aircraft manufacturer or production certificate holder as being limited to a total life counted in hours, cycles, landings, or by calendar.

A technician installing a life-limited part is responsible for, and should be held accountable for, recording all of the pertinent information regarding the part and its replacement in the appropriate maintenance records. This includes documentation of the part removed as well.

Another type of life-limited parts that receiving inspectors should be aware of are those that have a limited shelf life. Parts that have a specific shelf life - a limit as to how long they are eligible to be used - must be identified in some fashion to ensure that they are not used in the maintenance of aircraft once the shelf life has expired. 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 such materials from the inventory before their shelf life has expired. When these types of materials are received, the receiving inspector should identify them in an obvious way.

Inspectors should also be aware of life-limited materials with a limit to the period of time the material remains usable after its container's seal has been broken. Such materials have what is termed a limited usable life.

An effective way to manage materials with a limited useful life is to mark the material with a date when it is opened. The marking usually occurs when they are purchased from the parts store and moved to the shop floor by the technicians. The most effective procedure I have seen is to mark those material containers with a colored dot when they are received from the vendor. The colored dot alerts the parts personnel to mark the check-out date on the material when it is checked out from the parts store.

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. A process should be in place that ensures the regular removal and proper disposal of these types of materials.

Certification of aircraft interior materials
Aircraft interior materials have a particularly unique traceability issue. When a lot of fabric or leather is received for use, it must be or have been burn tested or "certified" for use in the aircraft. All interior materials must meet certain flammability requirements to be eligible for aircraft installation. Many repair stations send pieces of these articles out for testing and certification after they have received them. And once the material is cut up for use, it is difficult to attach the certification paperwork to it.

One solution is to isolate the materials to be used for a particular aircraft and keep the certification paperwork for all materials for that aircraft in a binder. Then, if there is ever a question regarding the burn certification, you can easily retrieve the appropriate paperwork. It is also recommended that you provide certification to the aircraft owner once the work is completed.

Developing and maintaining an adequate parts management program will make it easy to demonstrate that you have only used approved aircraft replacement parts and materials.


Joe Hertzler is the president of AVTRAK Inc., an Aurora, Colorado-based company. Joe is an A&P mechanic with Inspection Authorization and also a private pilot.

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