The FAA has published for public comment a draft advisory circular on “Uncontrollable High Engine Thrust/Power (UHT) Failure Conditions.”
The draft AC interprets 14 C.F.R. § 25.901(c) to require that the safety analysis include an analysis of UHT failures. Under this new interpretation, when PMA parts potentially affect the powerplant or the APU, or if they affect the interface between airframe and engine/APU, it appears that the FAA may ask future applicants to meet 25.901(c). Potentially, this could be applied to each aircraft on which the engine or APU is eligible for installation.
The regulation being interpreted currently reads as follows:
c) For each powerplant and auxiliary power unit installation, it must be established that no single failure or malfunction or probable combination of failures will jeopardize the safe operation of the airplane except that the failure of structural elements need not be considered if the probability of such failure is extremely remote.
This new interpretation appears to be a burden that was not anticipated at the time that the regulation was promulgated. Subsection (c) was originally promulgated in 1970, and originally merely required that the 25.1309 analysis be performed (the preamble to the final rule clarified that this was sufficient). In 1970, the analysis was supposed to be an installation fault analysis. The rule was changed in 1977 in order to “provide for a higher degree of airplane-engine compatibility.” But the UHT issue appears to be unrelated to airplane-engine compatibility, so requiring this as an element of the 25.901(c) analysis seems like an expansion of what the regulation was designed to require. Such an expansion of scope typically requires an amendment to the the regulation.
Moreover, it appears that the FAA has anticipated that the burden of this new analysis might be unreasonable, and therefore they have specifically invited design approval applicants to petition for exemption from this provision (the invitation exists within the body of the draft AC).
Do you see any impact to your PMAs (current or future)? How does this affect your business? Let us know so that MARPA’s comments on this policy can reflect your interests.
Comments on this draft AC are due to the FAA by September 4, 2017. We would appreciate your comments to MARPA by August 28, so we can reflect them in our own comments.