Be Legal - Document your Aircraft Parameter Configuration

Before any flight data can be examined, an electronic Data Frame Definition (or Parameter File) must be created to convert Raw Data into Engineering Units from a traceable engineering document. This document may be part of the DFDAU Specification Control Document or even an STC Correlation Test. There is currently no Industry Standard format.

Recently published FAA Advisory Circular 20-141 provides excellent guidance on such a document’s minimum content. Necessary information includes, but is not limited to, Word Number, Bits, Sub-frame(s), Super-frame Cycle, Polynomial Coefficients, Data Source, Units of Measure, Positive Sense, etc.

Airlines purchasing legacy aircraft, which have endured numerous DFDR system upgrades, often find their data is incomplete. The proper course of action is to either engage their engineering department or contract one of several consulting firms to examine the aircraft and fill in the missing information. Measurements will need to be correlated against monitored raw data to create and/or verify formulae.

AC 20-141 also provides guidance on the proper calculation of the Correlation Coefficient,
a measurement that ensures sufficient agreement between calculated formulae and
real-world observations (measurements). These are primarily useful for analog
(particularly nonlinear) parameters where a curve-fit is performed to arrive at a formula.

Often, this is the most challenging facet of setting up a DFDR Continued
Airworthiness Program.

Avionica can review your documentation and determine whether it is compliant with the regs. If not, we can upgrade your documents and provide you with both paper AND electronic documentation compliant with the emerging standard, ARINC-647. Contact Avionica to discuss your requirements.