Title 14 of the Code of Federal Regulations (14 CFR) 121.133 requires maintaining aircraft publication currency. However, the language leaves it wide open to interpretation.
The popular belief in the industry is that currency pertains to maintaining publications to the latest Original Equipment Manufacturer (OEM) revision. This may be true for the OEM “known” or delivered configurations, but not for operator-driven modifications.
The OEM known configuration is the delivered configuration plus any reported service bulletin accomplishment. OEM-placed Customer Originated Changes (COCs) are NOT considered an OEM known configuration. They are the operator’s responsibility to maintain, and the OEM does not typically consider them during their revision process.
The operator is responsible for ensuring that all configuration changes are provided for. This means addressing all parts, wiring, procedures and troubleshooting, and ensuring that they are in a format that is accessible, easy to use and “acceptable to the Administrator”.
Unstructured and non-compliant supplements loosely replicating the OEM’s conventions for the “post-mod” configuration are the industry standard. Operators submit “post only” supplements to the FAA Aircraft Evaluation Group (AEG) for Instructions for Continued Airworthiness (ICA) approval. The operators then use these same supplements to support the maintenance of the new configuration.
These supplements fall short for long-term use in several ways:
- They seldom address schematic diagrams, an invaluable tool for initial troubleshooting and system overview.
- Wiring diagram changes only address the diagram sheets that the system modifications directly affect. They do not address the redirection of references on associated diagrams. This makes following the unaltered circuit portion to the modified portion very difficult.
- The modification-related changes exist separately from the OEM source. Operator procedures typically direct the Technician to review the supplements first. However, the extent of the modification is not always obvious. This makes choosing between the OEM manual or the supplement difficult at best.
- Manufacturers often deliver the supplements in formats and structures that do not comply with industry standards. The Air Transport Association of America (ATA) prescribes these standards, and they are widely accepted by airline operators worldwide.
The bottom line: complex modifications and poor supplemental data create contradictions between the OEM source and the supplement. If technicians use them incorrectly, delays and aircraft misconfigurations occur.
It is understandable that an aircraft’s initial operation following a Supplemental Type Certificate (STC) modification will not wait for the full integration of the supplements into the OEM publication. However, long-term use of a supplement increases human factors risks and impact of delays.
In extreme cases where operators never or rarely incorporate supplements, overlapping of supplemental content exists. This forces the technician to piece together the supplements as well as the OEM publication to understand the current configuration. In these cases, delays and the risk of misconfiguration amplify exponentially.
