Certification specifications (CS) 27.1337(e) and 29.1337(e) require the installation of chip detectors to detect particles of ferromagnetic material that are released by elements of rotor drive systems as a result of damage or wear.
Additionally, chip detectors are frequently identified, and accepted, as one of the compensating provisions for hazardous or catastrophic failures in the design assessment (refer to CS 29.917(b)). However, there is no explicit provision in the CSs, nor any detailed AMC, for consistently demonstrating that chip detectors perform their intended function.
In-service experience shows that there have been occurrences where the chip detection system was not capable of indicating the presence of wear or degradation of elements of rotorcraft gearboxes, even if resulting particles were present in the system for some time before a failure occurred. Therefore, the specific objective of this proposal is to ensure that an acceptable minimum level of effectiveness is achieved by the chip detection systems installed in rotorcraft drive systems.
This objective will be achieved by:
- introducing a new objective-based certification requirement for the demonstration of the performance of a chip detection system (Subtask 1); and
- assessing whether it is necessary to implement a proportionate retroactive application of the certification requirements to the existing fleets and/or to the future production of type-certified rotorcraft (Subtask 2).