Can an unserviceable component be fitted on a serviceable aircraft for a maintenance check? I was doing some reading on aviation regulations and I wanted to understand from an expert whether the following situation is allowable or not. I have reviewed EASA continuing-airworthiness guidelines but am still unclear as this is a bit of a unique scenario.
Appreciate if you can shed some light on whether this situation is permissible or not.

A component fails and is removed from Aircraft A and declared unserviceable (with an &quot;unserviceable&quot; tag).
A similar component is removed, via robbery/cannibalisation, from another aircraft (Aircraft B) undergoing maintenance activity (A or C check), and provided to Aircraft C, which has a similar failure.
There is now a &quot;hole&quot; in Aircraft B, since the component has been robbed/cannibalised to support Aircraft C for the latter's maintenance requirement.
The original failed component (from Aircraft A) which was declared unserviceable (with an &quot;unserviceable&quot; tag) will be used to support the maintenance check inspections/tests for Aircraft B.
These tests are to inspect/test aircraft systems, and the &quot;hole&quot; needs to be plugged to carry those out.
The unserviceable component will eventually be removed from Aircraft B as unserviceable (with the &quot;unserviceable&quot; tag).
EASA Regulations do not specifically preclude you from doing what you are planning to. They leave an awful lot of room for interpretation. How you do your maintenance is up to you, as long as you meet the core requirements and that your processes can be audited.
Additional rules for this type of activity would normally covered by a local procedure (such as Robbery). If you do not have a covering procedure internally then you should absolutely be checking with your Quality Assurance department to validate your actions before undertaking the procedure.