Star pilot regularly forms part of this group (4)
I believe the answer is:
trio
'part of this group' is the definition.
'trio' can be an answer for 'group' (a group of three). I am unsure of the 'part of this' bit.
'star pilot regularly' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'star'+'pilot'='starpilot'
The alternate letters of 'starpilot' are 'TRIO'.
'forms' is the link.
Can you help me to learn more?
(Other definitions for trio that I've seen before include "Small group playing" , "Riot (anag)" , "Group of Magi?" , "Musical group" , "Beethoven's 'Archduke': famous piece written for this ensemble" .)