Perhaps AH should revisit its response the their reply to the following REDL safety recommendation (in AAIB annual report 2012)
SAFETY RECOMMENDATION – 2011-032
It is recommended that, in addition to the current methods of gearbox condition monitoring on the AS332 L2 and EC225, Eurocopter should introduce further means of identifying in-service gearbox component degradation, such as debris analysis of the main gearbox oil.
Response
Based on FMECA (Failure Mode Effect and Criticity Analysis) and confirmed by the experience, two types of debris can be generated by gearbox deterioration:
3D-particles (volume) or 2D-particles (surface): these types of particles are usually generated by degradation of high-loaded functional surfaces like bearing races or gear tooth (spalling, scale, flaking ...) or by part breakages.
- Wear particles: these types of abrasive particles are usually caused by abnormal high-contact of surfaces (fretting, micro-pitting...) and are generally in suspension in the oil.
A third type of debris can be found in gearboxes is associated with the manufacturing process (swarf...), the assembly process (piece of lockwire, fragment of cotter pin...), or maintenance actions (leading to introduction of foreign objects). All these debris are considered as some 3D or 2D particles.
Because the types of these generated particles are very different, adapted monitoring means must be used in order to monitor each type.
Two monitoring means are presently available to detect such debris:
- Magnetic plugs: these collect the particles and are visually inspected in order to detect 3D or 2D debris, but they can also collect wear particles. An electrical system can be added in order to give an in-service information of particle presence (warning on pilot on instrument panel and/or HUMS system for the maintenance) as soon as the particle(s) collected is (are) able to close the bridge between the two electrical parts of a magnetic plug. All Eurocopter fleet gearboxes are equipped with magnetic plugs (manual or electrical ones) and this is the main monitoring means to detect internal gearbox component degradation (they are also associated to the oil filter cartridge inspection).
- Spectrometric Oil Analysis Program (SOAP): this is used to monitor evolution of the concentration of different metals or else (particle per million) in suspension in the lubricant. It requires following of a dedicated and strict procedure to take periodically a volume of oil in defined conditions (warm and mixed oil taken with specific equipment by qualified personnel with a qualified process) and sending it to qualified laboratory.
SOAP is a monitoring means that is well known to Eurocopter and its principle is described in EC Technical Publications (Standard Practice Manual WC 20.08.02.601 attached). SOAP is considered by Eurocopter as an optional and additional monitoring means. SOAP can be used to monitor the evolution, between two oil replacements, of metallic material concentration or possibly some other material (like mineral) which are in suspension in the oil. SOAP can trigger the requirement of a close monitoring of the main monitoring means (magnetic plugs and filter) if certain dedicated thresholds are exceeded.
This means was introduced in the past during the development of SA 330 (Puma) and at the beginning of AS 332 (Super-Puma) production because the technologies used (bolted assemblies, machining without grinding, etc.) sometimes produced wear particles. This is no longer the case as a result of modern technologies used on the AS332 L2 and EC225 main gear boxes (Electron beam welding instead of bolted assemblies) and manufacturing processes (super finishing, grinding) which generate parts more reliable regarding wear degradation.
Despite the fact that these old technologies could generate some wear particles relevant to SOAP, the experience of Eurocopter demonstrates that this means was not efficient and that, in practice, it had led to many unjustified removals of gear boxes with unnecessarily interference to flight operations and wasted maintenance costs. Against this background, Eurocopter so issued Service Letter 759-00-86 in 1986 25/06/1986.
It also has to be noted that SOAP is not adapted to detect 3D or 2D particles because such particles are not in suspension in the oil. So SOAP is not adapted to detect spalling.
In addition, the magnetic plugs are able to detect incipient spalling at a level where, even if the whole volume of particles generated was in suspension in the oil, the concentration would not be detectable by SOAP taking in account the important oil volume in a main gear box.
Eurocopter considers that magnetic plugs and/or chip detectors are the most efficient means to detect gearbox internal failure modes, and that they are sufficient to ensure the flight safety so that further means of identifying in-service gearbox component degradation, such as debris analysis of the main gearbox oil, are not necessary. Here, it is relevant to note that the particle detection capability of the sump and epicyclic plugs has been enhanced by the removal of the ring of magnets from the lower area of the epicyclic module.”
Status - Rejected
It seems EC/AH got hung up on SOAP and MCDs rather than looking at other methods of monitoring.