The FAA is has amended the airworthiness standards for airplane propellers to require TC applicants to identify critical parts.
The FAA claims that this new requirement will increase the margin of safety and also harmonize the U.S. rules with those of Europe.
The rule change affects subsections (c) and (d) of section 35.15 of the FAA regulations by revising them to the following language:
c) The primary failures of certain single propeller elements (for example, blades) cannot be sensibly estimated in numerical terms. If the failure of such elements is likely to result in hazardous propeller effects, those elements must be identified as propeller critical parts.
(d) For propeller critical parts, applicants must meet the prescribed integrity specifications of Sec. 35.16. These instances must be stated in the safety analysis.
The change in subsection (c) is that the prior language merely said that in such cases compliance may
be shown by reliance on the prescribed integrity requirements of part 35 – now these parts will have to be defined as “critical.” In particular, single failure elements of a propeller whose failure is likely to result in a hazardous propeller effect would be described as “critical.”
The prior subsection (d) says that if the propeller relies on a safety system to prevent failure, then the failure analysis must assess the possibility of a failure in the safety system. Under the new language, The new language will defer the analysis of critical parts to the new language of 35.16.
The rule change added a new section 35.16 that reads as follows:
Sec. 35.16 Propeller Critical Parts.
The integrity of each propeller critical part identified by the safety analysis required by Sec. 35.15 must be established by:
(a) A defined engineering process for ensuring the integrity of the propeller critical part throughout its service life,
(b) A defined manufacturing process that identifies the requirements to consistently produce the propeller critical part as required by the engineering process, and
(c) A defined service management process that identifies the continued airworthiness requirements of the propeller critical part as required by the engineering process.
PMA manufacturers that produce propeller parts will want to look carefully at the effect this could have on future designs, and on their ability to get the FAA to approved those parts if they are deemed to be critical parts. It is also worth noting that EASA applies different standards to the import of PMAed critical parts (they are not automatically accepted and the exporter needs to obtain an EASA STC for the parts) so it will important to consider what affect this might have on your exports.
This final rule becomes effective as of March 19, 2013.