Fliers, for example, and engineers test regularly (6)
I believe the answer is:
egrets
'fliers' is the definition.
(egret is a kind of bird)
'example and engineers test regularly' is the wordplay.
'example' becomes 'eg'.
'and' means one lot of letters go next to another.
'engineers' becomes 're' (Royal Engineers).
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
The alternate letters of 'test' are 'ts'.
'eg'+'re'+'ts'='EGRETS'
'for' acts as a link.
(Other definitions for egrets that I've seen before include "waders" , "White wading birds" , "Greets in way of certain herons (" , "Greets like certain herons" , "Fliers" .)