Publication Currency - Shedding Some Light on 14 CFR 121.133


Maintaining aircraft publication currency is required by Title 14 of the Code of Federal Regulations (14 CFR) 121.133; however the language used 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; it is not true, however, 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 and are the operator’s responsibility to maintain and do not typically get any consideration by the OEM during their revision process.

The operator is responsible for ensuring that all configuration changes are provided for. This means parts, wiring, procedures and troubleshooting must be addressed and be 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. The “post only” supplements used for submittal to the Federal Aviation Administration (FAA) Aircraft Evaluation Group (AEG), for approval as part of the Instructions for Continued Airworthiness (ICA) are then used by the operator to support the maintenance of the new configuration. These supplements fall short for long term use in several ways:

  1. They seldom address schematic diagrams, an invaluable tool for initial trouble shooting and system overview.
  2. Wiring diagram changes only address the diagram sheets directly affected by the system modifications and do not address the redirection of references on associated diagrams, making it very difficult to follow the unaltered portion of the circuit to the modified portion.
  3. The modification related changes are fragmented 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 making the choice of using the OEM manual or the supplement first difficult at best.
  4. The supplements are often delivered in formats and structures that do not comply with industry standards prescribed by the Air Transport Association of America (ATA) and widely accepted by airline operators worldwide.

The bottom line is that due to the complex modifications and poor supplemental data, there are contradictions between the OEM source and the supplement and if used incorrectly, delays and aircraft misconfigurations occur.

It is understandable that an aircraft 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 supplements are never or rarely incorporated, overlapping of supplemental content exists, resulting in the technician having 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 are amplified exponentially.