Often, something like a hydraulic pump or a TKS pump is thrown away, with a few thousand $ or € wasted – because allegedly since there is no CMM (component maintenance manual) for it which means no legal repair to it is possible – other than (allegedly) by the original manufacturer only (who may be no longer around, or be simply a useless unresponsive company).
What is the exact legal position for rewinding such a motor?
AIUI, on an N-reg you can just get it rewound (which may involve rebuilding the commutator) and an A&P can return it to service.
On an EASA-reg, you might need to find a Part 145 company whose scope includes motor rebuilding (good luck with that one) and they can generate a fresh EASA-1 form for it (an 8130-3 is no good because it is no longer a “new” part, allegedly).
Back to N-reg, is it really true that with no CMM a part cannot be repaired? It is a position often quoted in the Socata owners’ group, though not by Socata itself.
What is the exact legal position for rewinding such a motor? AIUI, on an N-reg you can just get it rewound (which may involve rebuilding the commutator) and an A&P can return it to service.
On an N-registered plane my understanding is that an A&P can perform and/or oversee the overhaul work being done (by anybody) and make a maintenance logbook entry saying that he (personally) overhauled the pump and checked the assembled system for proper function. It starts to get trickier if he is replacing internal components. The closer the plane is to antique. classic, unusual or ‘unsupported’ you can bet the more generic the logbook entry will likely become. What really matters is that the next annual inspection is signed off by the IA, and that technically correct work was done to make it function properly.
I had such a question come up last year when I asked my A&P/IA to disassemble and clean my roll trim motor. He said this would be illegal to do in the field. OTOH, I have heard of other people who have done exactly this.
Under EASA, you need to have the original overhaul instructions from the manufacturer in order to overhaul. Alternatively you need to be a Part 21 design organization and develop your own method.
When the component is listed with a life limit in the maintenance manual, you have to bite the bullet in EASA land (unless excluded in your approved airworthiness management program). When it’s not listed, then you can be more pragmatic but the documents will not reflect that pragmatism…
One example is S-TEC servos. Officially only S-TEC can repair / overhaul them which they introduced a few years ago to keep their crumbling business afloat. In real life, avionics companies can do it too (probably better as well) but they cannot document it.
Yes, but one always has to be careful with that very broad term “life limit”.
Generallly speaking, it depends whether this derives from section 04 (“airworthiness limitations”) or from section 05 (“time limits and maintenance checks”) of the MM. Only the former are strictly mandatory; the latter are manufacturer recommended.
However, many CAAs around the world are known for disregarding this principle, citing that maintenance needs to be done “according to manufacturers’ instructions”…
That heavily depends on the structure of the maintenance manual which is not as uniform as POHs. For Cessnas it would be section 02 (inspections). The newer the aircraft, the more the vendor tends to write about these things in the MM. In some cases, vendors have added these limitations in a later revision of the MM. Under FAA Part 91 this stuff can be mostly ignored but in EASA land only certain things at the discretion of your CAA can be ignored.
I guess the Cirrus is the “worst” of all in that it has a very extensive list of life time limited components.
I guess the Cirrus is the “worst” of all in that it has a very extensive list of life time limited components.
Yes, but again, only as far as “recommended TBOs” go. The "limitations "section of the MM is actually very short and only has one handful of items (one of which being the expensive parachute replacement…14k€ every ten years).
And: all the rest does not directly depend on EASA, but so far still on the respective CAA of the country of registration. For example, in the first few years after the Cirrus was type-certified by EASA (2003 or so), the LBA simply made all the items under section 05 mandatory, including stupid stuff like gascolator seals every 5 years and so on. It was only after years of interaction with the LBA that many of these items are now deemed “on condition”. But in other EASA countries, it is still all mandatory.
Is there any definition of what “A&P supervision” is supposed to be?
Clearly it cannot be direct 100% supervision otherwise aircraft maintenance by non-A&P (and non-EASA66 – same issue in EASA-land) engineers could not be done, and on the job training would be impossible.
Motor rewinding is a big business which made me wonder why people throw away stuff like hydraulic power packs at $5000 each. The pump portion is unlikely to have failed. What packs up, sure as death or taxes, is the brushed DC motor!
Actually the motor rarely needs rewinding unless it is burnt out. What goes is the commutator and/or the brushes. There are various interesting ways of rebuilding a commutator. One can even rebuild one completely from nothing, if one has a lathe and preferably a turret mill with an indexing head.
Is there any definition of what “A&P supervision” is supposed to be?
Under FAA rules I believe a person working under the supervision of a holder of a mechanic or repairman certificate may perform the maintenance, preventive maintenance, and alterations that his supervisor is authorized to perform, if the supervisor personally observes the work being done to the extent necessary to ensure that it is being done properly and if the supervisor is readily available, in person, for consultation.
Most people interpret that to mean the A&P does not have to be continuously on site, but he must be readily available on site. Also since the A&P is taking total responsibility for the results of the work, that he must feel comfortable that the work was done correctly. Overhauling or repairing a component should not extend to the point of changing its detail and manufacturing design 
I would personally want that the component be essentially indistinguishable from original after work is complete, unless there is approved repair data like AC 41.13 etc. that can be referenced by the logbook entry. Best not to go too far if you think it might under any circumstance become an issue.
I had such a question come up last year when I asked my A&P/IA to disassemble and clean my roll trim motor. He said this would be illegal to do in the field. OTOH, I have heard of other people who have done exactly this.
Without commenting on this specific incident, I do think people get confused between the legality of an A&P doing a one-off field repair on a specific airframe followed by his logbook entry specific to the aircraft, and the separate legality of operating a component overhaul shop.
Also worth noting that anybody can legally disassemble something, make it unairworthy and take it out of service. Under FAA regs the collection of parts can then in general be assembled and brought back into service by appropriate A&P mechanic efforts and an appropriate maintenance logbook entry. As usual, there are exceptions – for instance turbocharged and geared engines both require an IA.
A separate issue is that MM and MM/Limitations issues are sometimes a factor driving people to buy and operate airframes that were certified long ago when airframe MMs were more rudimentary.
A separate issue is that MM and MM/Limitations issues are sometimes a factor driving people to buy and operate airframes that were certified long ago when airframe MMs were more rudimentary.
Unfortunately in EASA land, a manufacturer can arbitrarily change the MM and introduce new limits which may become binding. It is a nice revenue generation scheme. Safest is probably to buy an aircraft from a defunct manufacturer…
