Helicap, who told you that the 139 has a composite tailboom?
The tailboom is composite construction, not composite materials.
The tailboom is Aluminium skins (Aluminum for you Nth American types
) bonded to an Aluminium or Nomex paper core. Nothing new there, the B212/412 use the same construction methods in the forward sections of their tailbooms, and have similar debonding issues (greatly reduced with Alpine Aero ejectors fitted).
There are next to no composite materials used in the construction of the AW139 from the codkpit doors back. Forward of the cockpit doors it is Kevlar, behind the cockpit doors is nearly all Aluminium.
Hope that clarifies things for you.