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By Duo802
I'm hoping that someone will be able to help out with this question, or at least point me in the right direction.
We have a Robin DR400/180Remorqueur that was originally built in 1975, but fully rebuilt by Robin in 1996, when it was fitted with a Gomolzig silencer kit. This is now completely knackered, and needs to be replaced. We want to replace it with the standard stub exhaust of the type that came with the aircraft originally but we've been told that we need design approval and it would be classed as a major mod, with all the hassle and cost that that would entail. This seems odd, given that a stub exhaust was the original fit, and I would have thought that it'd just be a case of reverting to original spec with little formality. After all, there are loads of other Remos in the UK with standard exhausts but I can't seem to get a straight answer on the subject, and so does anyone know the answer to this and, if possible, can they point me to the official EASA or CAA words on the matter (if such a document exists)? Trying to find the definitive answer in all the EASA and CAA bumf has almost got me to the wrist slitting stage!

In pedantic theory you need a modification to remove the original silencer mod, but...

If you have the installation data (drawings/instructions) for the silencer installation then you have a good chance. With that data you can claim to know everything that was done to the aircraft to fit the silencer and thus can reliably 'undo' it fully.

I'd have thought that your maintenance organisation would then be 'sensible' and revert to the original kit on the basis that they knew that they had reverted to the original spec.

If you don't have the silencer mod data then they still should be able to revert to standard if they can be sure of doing that correctly in accordance with the standard Aircraft Maintenance Manual and Illustrate Parts Catalogue. An exhaust system, although vital, is not a particularly complicated installation after all.

Unless your maintainer has a good reason not to do this then I'd be asking them to explain their rationale.
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By Duo802
Thanks for your helpful input. We have determined from the 1996 Robin paperwork (when the aircraft had a factory refurbish) that the exhaust is listed under the Supplementary Equipment List as “silencieux ¼ d’onde”, part No This part number is the one for the complete kit of parts, including manifolds, silencer and all fixings.
The Supplementary Equipment List is all of the non standard parts fitted, such as Radio, VOR, Transponder, Auxiliary fuel tank, so all of the option items not included in a standard aircraft. Hence the complete exhaust system, from manifolds to silencer, is not the standard item and therefore it should not be a problem to simply revert to the standard fitting. However, our engineer doesn't seem to want to accept this.