Parts removed for troublesgooting reason
 

I would like to ask how are you dealing with the parts which are removed from aircraft for troubleshooting.
Let's imagine that aircraft engineer removed the part and installed new one i.a.w. T/S procedure suspected to be the cause of the problem, after that the fault still present.
Aircraft was dispatched i.a.w. MEL after few legs, next steps of T/S was performed. The fault was cleared after different component replacement.

My question is what are the conditions under which the part removed at the beginning of T/s can be consider as serviceble without workshop approval?
What about EASA Form 1?

Thank you for any ideas.

Operators often have a "hold procedure" for parts removed during troubleshooting and subsequently found serviceable. They will be refitted IAW this procedure and the other part returned to stock.

Airlines have instituted this process in different ways, I am not a fan of this. We have enough parts removed U/S and fix a problem, that part may hit a bench, go under their automated bite check and are returned with no fault found. With a system that has history I often check the part's repair history for NFF returns and resort to swapping with a known good one to see if the problem follows the part.

Parts removed for troublesgooting reason
 

We have a CASH program for this kind of thing. If the part/CPN is in the CASH program it is held on the quarantine shelf on a quarantine tag. If there is no repeat in 3 days then an unserviceable tag is printed automatically to the station. If there is a repeat a serviceable tag is printed and it is returned to stock. Not a fan.

Big Airways used to run a 'STAC' system. Suspect parts were removed, tagged with a STAC label and placed in a separate storage area. Subject To Aircraft Check they would be declared either 's' or 'u/s' after a few days depending on whether or not the removal cured the fault or not. It was, however, limited to mainly 'black box' type LRUs that were not contaminated with fluids or dirt.

I don' know if they still use the system.

STAC
 

The system is still in use I changed a hydraulic engine driven pump which had been removed in elimination of a hydraulic leak. The pump came from the stores with a STAC label attached.

The system is still in use but strictly controlled and monitored . The system does NOT allow any item with hydraulic, oil , or fuel components as well as other conditions and limitations.
In my experience nearly all items in the STAC system are avionic components .
Used correctly it is a good system that saves money , while still maintaining the safety of the aircraft .

STAC
 

Fancy hearing about STAC again. When on the ramp as an avionic LAE or something similar, I was expected to check out and decide yea or nay on serviceability in my increasingly rare 'spare time', it was a bit of a bane but was on my 'KPI's'.
As said previously, it was avionic only with no fluid contaminated components. For avionics systems with all those 'now you see it and now you dont, faults it could work well, and many components could be quickly identified as 'S' as the same fault continued.