Parts: The lifeblood of aviation

Yesterday was Saturday. Like many Saturdays in corporate aviation, it was simply one of two days between Friday and Monday. My reason for being at work was to assist in the replacement of a part on an aircraft that was scheduled to depart the next day. We discovered the failure during a routine pre-departure check and tried to obtain a replacement from the airframe manufacturer. Unfortunately, the aircraft in question is out of production and the OEM is more inclined to stock parts for currently manufactured airframes. Plan B was to contact reputable vendors likely to stock our required component and have it shipped in for a Saturday delivery.

Some thoughts came to mind while contemplating the whole process. The supply of quality parts is the lifeblood of aviation and includes the accompanying restrictions and debilitating circumstance.

Replacement necessary
Procuring the correct part begins with the technician’s decision that a replacement is necessary. Research is frequently the first step in obtaining a replacement component. What factors are to be considered? If the aircraft is registered in the United States, the Federal Aviation Administration (FAA) has some established guidelines. Although there is no official definition of the word “airworthy” in the Code of Federal Regulations (CFR) Part 14, it is implied that for an aircraft to comply it must: “Conform to its type certificate (TC). A product conforms to its TC when its configuration and the components installed are as described in the drawings, specifications, and other data that are part of the TC, which includes any Supplemental Type Certificates (STC), Airworthiness Directives (AD), and field approved alterations incorporated into the product; and the aircraft (product) must be in a condition for safe operation.”

Note: If one or more of these conditions are not satisfied, the aircraft or product would be considered not airworthy.

Part selection
The type certificate is a good place to begin the quest. It is unlikely that the TC will contain a complete list of parts but it will provide the guidance as to which documents may be used to assist in selecting the appropriate device. In many cases the FAA will not approve all of the supporting documents for a specific aircraft type but will label such things as maintenance manuals, service bulletins, and parts catalogs as “Acceptable Material.” Ascertaining applicability is the next step in the process. Unfortunately, the fact that a part is listed in a parts catalog does not mean it is correct for the aircraft specific configuration.

An Air Data Computer may have several versions; if the aircraft operates in reduced vertical separation minimums (RVSM) conditions, an STC may provide the required part number and may be contradictory to the aircraft parts catalog. The “black boxes” used in avionic suites will sometimes have different modification levels and the part number of a replacement unit may be predicated on other devices in the system. This can often be a dilemma, especially when you are advised that a part number has been superseded.

One recent experience involved replacing one of three integrated avionics computers. Initial contact revealed no availability of the specific part number. Communication ensued with the aircraft manufacturer’s help line and a service bulletin came to light that provided the authorization to utilize a later version of the failed device. The order was placed, the component arrived, and the technician involved in the project fortunately had the foresight to read the applicable service bulletin prior to installing the new computer. The manufacturer was correct in that this new part number could be used, as long as the other two computers were upgraded at the same time. Further telephone contacts located the correct part number and financial ruin was averted.