Bits of shell from planes flying across there regularly (8)
I believe the answer is:
shrapnel
'bits of shell' is the definition.
(bits of a bomb)
'planes flying across there regularly' is the wordplay.
'flying' indicates anagramming the letters (letters fly around into new positions).
'across' indicates putting letters inside.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
The alternating letters of 'there' are 'hr'.
'planes' anagrammed gives 'sapnel'.
'sapnel' placed around 'hr' is 'SHRAPNEL'.
'from' acts as a link.
(Other definitions for shrapnel that I've seen before include "Bits of shelling" , "Colloquially, small change" , "Projectile fragments" , "Exploding shell fragments" , "Dangerous fragments" .)